HPH332 : How accurate are Energy Performance Certificates (EPCs)? – with Tom Gwilliam

May 3, 2023 by Ben Leave a Comment

Tom Gwilliam explains what Energy Performance Certificates (EPCs) are, how they are created and why they are unlikely to be a useful measure of how energy efficient a building is.

Interview with Tom Gwilliam

Tom is a sustainability consultant at Etude, with a background in structural engineering, energy assessment and whole life carbon analysis. This episode was inspired by a previous episode, Should we celebrate architecture that performs poorly?, which relied heavily on EPC data.

EPCs are a legal requirement when selling or renting a home

Energy Performance Certificates give a rating between A and G, and a number between one and 100, of how energy efficient the home is. This is the main output, but there’s also other information about what you might do with the home and how the home is performing at the moment.

A domestic energy assessor carries out a SAP assessment on new-builds, or an on-construction domestic energy assessor carries out a ‘reduced data’ SAP (RdSAP) assessment on an existing building. The two are different, but both rely on entering information into a computer model, which outputs the EPC.

SAP assessments make assumptions about how a building operates

SAP stands for the Standard Assessment Procedure. It measures heat loss, domestic hot water use, energy associated with pumps and fans, and the energy associated with lighting. It also estimates what people might use for appliances (‘unregulated energy’, because it varies by number of occupants and their behaviour).

The assessment makes various assumptions and boils them down to a single number for total energy use in kilowatt hours. On top of that, it superimposes carbon emissions, primary energy, and other metrics used for building regulations compliance.

EPCs also measure the cost of operating the building

The EPC process takes the total energy figure and puts a cost on it for the resident. But the accuracy of that cost all depends on the accuracy of the assumptions made earlier in the calculation.

SAP is used to drive policy decisions

There's an aspiration for every property in the UK to be at least EPC C by 2035. Part of the problem is that studies show the EPC rating doesn’t correlate well with the energy use of a building. You’d expect that moving from A to G would see increased energy use, but there isn’t much change in general.

Even if all homes are a C by 2035, we’re unlikely to see much change in energy use in buildings. We’ll still have high energy homes and it will be too late in 2035. There’s a real incentivisation issue, and no strong grasp of how to improve buildings through the EPC process.

Five different assessors would probably come up with five different EPCs

Another major problem with EPCs is consistency – there is none. The EPC industry is not well-moderated, and assessors are paid quite poorly. Plus, there’s pressure at government level from house builders not to increase the cost of assessments and EPCs.

The process relies on a person to interpret a physical characteristic of a building. People might measure things differently or inaccurately, or even completely wrong. Assessors also have to make a judgment on how old a building is, and how it’s constructed. They don’t have the time or money to investigate what’s actually in the walls, so a lot of their work is guessing and being as quick as they can.

There's proven evidence of getting an EPC for a new-build house, then sending an RdSAP assessor to do an assessment the next day, and the two producing completely different results.

Example of an Energy Performance Certificate

EPCs aren’t really about your home, even though they look like it

An EPC is presented in a way that makes you think that it's about your home, but it isn’t. If you had identical buildings in Cornwall and Durham, and carried out identical assessments, you’d get the same EPC. But we know the space heating demands for buildings in those two locations will be very different. That fundamentally undermines the EPC process.

SAP doesn’t have the ‘as built’ check that Passivhaus does

It's possible to game the system, particularly with new-builds. SAP assessors don't get paid well and they have to take the word of the developer or people on site. Assessors don't have the required understanding of how a building is going to perform in reality. They don't see all the detail, so they have to simplify things and make assumptions.

When you have that disconnect between what’s happening in reality and what the computer model says, there's a big incentive for developers to be unrealistic with what they're saying. By contrast, two people carry out the Passivhaus process. There’s a designer and a certifier, and a peer review process going on all the time. It makes it a better-quality process.

Simply adding a requirement for the SAP assessor to go to site at the end of construction would make a big difference.

Thermal bridging is a particular issue

Thermal bridging is a big source of heat loss in new-build properties. SAP has categories for thermal bridges, but they don’t cover everything. It’s hard to have a 3D understanding of a building when working off plans, so if you’re not on site and seeing where thermal bridges are occurring then they’re not getting picked up at all. There's no way of quality checking that process because nobody is overseeing the SAP assessor.

There are lots of assumptions about heating system performance

The technology behind boilers and, in particular, heat pumps has lots of nuances. SAP doesn’t require the level of detail that influences whether heat pumps perform really efficiently or very poorly. The model doesn’t ask for a lot of information about the system, so it can only make a simplified judgement about how it will perform.

A way to improve it would be to break the system down into more component parts, understand each part better, and reflect that in the calculation with evidence. If we’re going to shift to low carbon buildings, SAP assessments should reflect a need for more information and understanding to incentivise developers as part of the building regulations compliance process.

Some people advocate for adopting Passivhaus

It’s a proven system. With Passivhaus and PHPP, there’s a clear link between designed on-paper performance and in-use performance. It’s a tick box exercise in some ways: being detailed in how you assess the building, understanding what is built on site, and making sure that's reflected in the calculation.

Doing more testing would reduce cost for the whole industry

We need to be able to survey our building stock at a level that gives us a better understanding of the energy performance of buildings, and not accept RdSAP as a minimum requirement. There is testing available, but it’s costly – and the only way to bring the cost down is to do more of it.

You can’t judge a building’s quality by its EPC

There is no information about indoor air quality, or other sustainability metrics. This is another area where Passivhaus excels. A Passivhaus is a good quality building that is pleasant to be in. We can't tell from an EPC how good a building is going to be, so it’s impossible to compare one A-rated building to another A-rated building.

Studies are highlighting the issues with EPCs

Etude carried out a research project looking at EPCs versus metered energy use. And UCL Energy Institute has just published a paper looking at buildings they’ve been monitoring over a long period of time. The conclusions all come back to the issue of assumptions made in the SAP assessment.

In addition, there are formulas within the SAP calculation that have been ‘locked in’ for years and they don’t change. The development of SAP over the last 20 years has been slow and it doesn't reflect modern buildings. People know there's an issue, but there's no process for SAP to be regularly updated. When changes are proposed they have to be consulted on, so it’s all very slow.

The Future Homes Standard is expected to change things

Because people know there are issues, an overhaul of SAP is expected alongside introducing the Future Homes Standard in 2025. If SAP changes, that obviously changes how EPCs are generated. It’s not clear how the government would reconcile the difference between existing EPCs and the future EPC system.

Home buyers can try to get hold of the SAP assessment behind the EPC…

…but it requires a bit of knowledge in order to sense check it.

Make sure ventilation systems have been entered correctly.
If a default value has been used for thermal bridging, you could try and work out if that's a fair assumption for your kind of building. Maybe ask on forums if it is a suitable way of measuring thermal bridging.
You could dig into the heating system and make sure what has been selected is what is actually in the building. Has the assessor selected all the right drop down boxes? Has a weather compensator been installed, for example.
Also look at what the assessment assumes for the occupancy of the building, because that drives a lot of energy use. You can see if it's related to how many people are going to live in the building.

If the numbers in the assessment don’t seem right then it's up to you whether you appoint someone else to look at it. PHPP, or an open-source version of SAP, is available so it’s an option to try and do it yourself, if you want to.

You’ll always need a SAP assessment because of building regulations…

…but it’s interesting to do a PHPP calculation as well and compare the two. Etude has worked with local authorities to help them understand how SAP differs from reality.

The local authority can’t mandate PHPP calculations, so Etude helps them to convert the SAP result to a more realistic number that can be measured against a policy target. The SAP inputs are still limited, but Etude can correct for known errors in the assessment.

Getting EPC ratings wrong is a problem for retrofit policy

Something needs to be done with RdSAP to make sure ratings are in line with what is expected for a building. As more homes are retrofitted, assessors will need to understand the age of the building, how it’s constructed, and where retrofit measures have already been put in place, in order to have confidence that improvements being made are actually going to make a material difference.

Find out more

Visit the website of Etude

Check out the UCL Energy Institute's research

Download the Passivhaus Trust's research report on EPCs

Transcript

Transcript of House Planning Help podcast – episode 332 (Tom Gwilliam)

What are the UK Passivhaus Awards?

If this award ceremony is not on your radar then you need to invest some time following the competition and delving into the archive. There have been some outstanding self build and retrofit projects in the hall of fame, so we recommend a lazy Sunday morning checking out the fact-files on the Passivhaus Trust website and watching some of the videos.

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HPH331 : What is a mechanical services engineer? – with Alan Clarke

April 12, 2023 by Lucy Cowell Leave a Comment

Alan Clarke explains the role of a mechanical services engineer on a low energy house build, in designing a heating and ventilation system that works efficiently and is affordable.

Interview with Alan Clarke

We've been fortunate enough to have Alan Clarke on the podcast before. Back in episode HPH062 we discussed with him whether a Passivhaus needs a heating system. In a later episode, he also explained the designs for the heating, ventilation, and hot and cold water systems for Ben's own self build.

Today, we welcome him back to conclude our mini-series, looking at different professions that we may need on our self build or retrofit project. Alan is a mechanical services engineer, with particular expertise in Passivhaus buildings.

Most mechanical services engineers will have a background in engineering

A mechanical services engineer will cover the design of the heating and ventilation systems of a building. Some practices would also do M&E (mechanical and electrical) or MEP (mechanical engineering and public health) work, which would cover all of the building services. As well as the heating and ventilation, that will be the electrical services, drainage and plumbing too. The majority of people practicing it professionally would come from an engineering training background.

Relevant parts of the building regulations are Part L and Part F

Part L of the building regulations covers the energy of the house as a whole, including the heating system. An electrical installer would be expected to be qualified and understand how to install a system that is going to be in line with the wiring regulations and building regulations compliance. This might include energy modeling of the building too.

Part F of the building regulations is to do with ventilation. Ventilation systems in houses are relatively new, and there isn't quite the same level of qualification and supervision.

Pre-planning is the ideal time to involve your mechanical services engineer

Not all architects will be familiar with integrating a mechanical ventilation system so that it works efficiently and is easy to maintain. There would be some spacial requirements at Stage 3 of the RIBA Stage of Works, but pre planning is the ideal time for an engineer to come in and think about where the main items of equipment are going to be located, and how the distribution through the building will work. Consideration also needs to be given in the design to accommodate the ductwork, although the detailed design for that would come later. If it's for a Passivhaus, there will also need to be PHPP energy modeling at this stage, before the planning application goes in. This will have an impact on the form of the building, window sizes, etc.

It is important to make sure the overall system is efficient

The energy efficiency of the overall system can be broken down into separate parts:

The MVHR unit – this must be an efficient piece of kit with good heat recovery efficiency and quiet, efficient fans. If the fans aren't quiet, people won't use it.
Good ductwork design – fan performance can be scuppered by putting in ducts that are too small, which means the fans have to work harder. They use more energy to run, and you get more noise. A good approach to the design of the ductwork is therefore important.

A further consideration in the Passivhaus analysis is heat loss, looking at how long the ducts are, and also how well insulated they are. Ideally, these should be as short as possible, just one or two metres length, which has implications on where to position the MVHR.

An MVHR unit also needs to have regular filter changes. Therefore, there's no point putting it somewhere inaccessible, where you can't see what you're doing!

There are two main ducting systems

The basic principles of a balanced mechanical ventilation system, are to bring in and supply fresh air to the rooms where we spend the most time, and take out stale air, particularly from the smelliest and wettest parts of the building. The extracted air passes through the MVHR which has a heat exchanger. This transfers practically all the warmth from that extracted air to the incoming air. Ductwork connects the ventilation unit to the rooms in the house.

A radial system uses lots of separate ducts that run to each room. If you want more air to go to or from a particular room then you run two ducts. Also, if it's got a long way to go, you might increase the number of ducts to a distant room to make it easier to get air from there to the MVHR.

The other system used is a branched system. You start with the biggest duct at the MVHR and run to the first room. At this terminal, it tees off to another room before branching off again, and so on. The duct size reduces as you go along.

Generally, the radial system ducts will have a diameter of 75 or 90mm, which is easier to thread through than the branched system, but you do need more of them. The branched system starts off at around 150-160mm, before dropping down to 100mm for individual rooms.

Space for the ducting will need to be allowed for in the structural and architectural design of the building, so it's good to know what system is going to be used as early as possible.

Air should be supplied into the rooms in a way that you don't feel a draft

For a flat ceiling, there would normally be a disc in the ceiling that spreads the air horizontally so that you don't feel it blowing on you.

The other type of supply valve is designed to go in a wall. This also spreads the air horizontally. The air flows are relatively small and mix with the room air quite quickly, meaning it's unnoticeable to occupants.

Around 2.5 litres of moisture is generated into the house per person per day

This is produced in a number of ways, such as:

Breathing and perspiration – this accounts for around a fifth of the moisture that we put in the house
Bathing – not just the hot water steam but also the towel and bath mat will continue drying back out into the room too
Water evaporation from the dishwasher drying cycle
Cooking – such as steam from boiling water
Laundry – drying washing indoors can mean there are several kilos of moisture that have to go somewhere

Without some way of extracting all this moisture, that's a lot of water that is just sitting in our houses. It can however be extracted through ventilation. Even on a wet day, the water vapour content of the external air is relatively low, and much less than the air indoors. Simply by bringing it in and exhausting the same volume of inside air, you can expel the water vapour.

Part F of the building regulations has guidance for calculating the ventilation flow rate that's needed. This is inferred from the number of bedrooms. A Passivhaus calculation is more specific and done on a per person basis.

It is more efficient to run the ventilation constantly

Many houses in the UK have intermittent extract fans, which just draw the vapour out when you have a bath or shower. Evidence shows however that this isn't effective in reducing humidity levels enough, leading to condensation and mould potential.

A house with an MVHR does focus on the wet areas, but has the ventilation running all of the time. There's not much to be gained by turning it off, as you're not losing any heat through it. Keeping the low power fans running continuously, rather than being off and then having to work hard for a while, is more energy efficient.

The primary benefit is to our health

Through living in an enclosed space, we generate a number of pollutants, some of which are a side effect of the moisture. The condensation and mould can be extremely detrimental to our health. Even at lower humidity levels dust mites can prevail, causing allergic reactions and asthma.

By ventilating a building we can also dilute and remove the VOCs and chemicals in the air that inevitably come out of the products.

Heat pump systems need to be designed carefully

Traditionally, a gas boiler with radiators has been a fairly resilient system for heating. Also, it's one which doesn't need too much oversight from an installer or heating engineer.

Although a Passivhaus only requires a small amount of heat, this will need to be delivered somehow. Alan commonly specifies heat pumps these days, however, he stresses that they must be designed and installed well.

Put a hot water cylinder where you are going to be using your hot water

It sounds obvious but is an important consideration. Positioning the cylinder centrally to where the hot water will be needed in the kitchen and bathrooms, means that you can have shorter pipe runs. Subsequently, there will be less heat lost through the pipes, and the hot water will reach the taps more quickly.

Most of a mechanical services engineer's work is before construction

A typical day for a mechanical services engineer might involve:

A discussion with the client to understand their requirements and how they might live in their house
A review of architect's designs
Planning the building services, distribution, emitters, ventilation terminals and key bits of plant on the layout drawings
Drawing up a specification. This is the shopping list for the contractors for the equipment needed. Also, it's the particular requirements for the installation, workmanship and commissioning
Working on the drawings/revisions – looking at where ventilation and hot water kit will go, positioning a heat pump, and considering any constraints around where that might go

When a client is building a house for the first time, the plans can sometimes evolve later in the process as they think more about what they really want. Ideally you should be executing the plans you have developed in the design stage during the construction stage, not altering them. This will make it harder for the whole team and more expensive for you.

Your mechanical services engineer needs to understand your priorities

They should listen and understand what their brief is. It's not helpful to have someone come in with preconceived ideas of a technically complicated piece of engineering, when the client just wanted something simple. It's a waste of their time and money.

Ideally, you also want your engineer to have enough experience to be able to look back on other projects to see what has and hasn't worked well.

Find out more

Follow Alan Clarke on Twitter

Transcript

Download a transcript of the interview with Alan Clarke

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HPH330 : What is a planning consultant? – with Andy Moger

March 29, 2023 by Lucy Cowell Leave a Comment

Andy Moger, from Tetlow King Planning, explains the role of a planning consultant and the benefits they can bring to a project.

Interview with Andy Moger

Andy is a planning consultant for Tetlow King Planning: a planning and development company based in Bristol that operates nationwide.

A number of years ago he worked on the government's first pilot scheme for self and custom build – the Heartlands project in Cornwall. Following that, he became more involved in the self and custom build sector, primarily doing work for the Right to Build taskforce. Nowadays, this sector is all he works on, dealing with applications, appeals and site promotions, ranging from single dwellings to larger developments and appeal work for some of the big house builders and strategic land promoters.

Not all building projects will require planning approval

It is possible to use ‘permitted development' rights for work like small extensions and loft conversions, depending on the extent of the area you're adding to your property.

The ‘prior approval' process typically applies to larger extensions. You inform the council who will notify your neighbours. If there haven't been any objections after a period of time then you're deemed to have consent.

Local plans control development in each area

Each council has to have a local plan; sometimes called a district plan or core strategy. These set out a strategic approach for that area for the next 15-20 years, and contain the policies that control development. If you're looking to get planning permission on a particular piece of land you will need to check your local plan to see how you fit with those policies, or how you might overcome any potential issues.

All of these plans will work on the basis of concentrating the development in the most sustainable locations, which will tend to be the largest settlements within an authority area. The settlement hierarchy is:

Towns and cities
Larger villages with a broad range of services
Smaller villages that have some facilities but still place a degree of reliance on higher-order settlements
Hamlets and open countryside where the presumption generally is against development happening unless there are specific circumstances, such as for essential agriculture

Start with a site appraisal

A planning consultant can carry out a site appraisal before you get to the application submission stage. This looks at a number of areas that might be a barrier to getting planning approval:

What the local policy position is
What the chances of adhering to those policies is
Site constraints, such as flood zones, ecological designations, conservation areas, nearby heritage assets, etc

This would be followed by a number of surveys and reports

Providing that the planning consultant thinks they can demonstrate that the project complies with the local plan, a number of surveys need to be carried out to support the planning application. These will depend on the scale of the development but it is likely that some will be requested.

An ecological report will typically be required to identify whether there are any protected species on the site and sometimes these can only be carried out at a specific time of year. If you miss a survey calendar window, you may need to wait until the following year before trying again.

Additionally, a transport statement will look at visibility splays and traffic generation from your scheme. Depending on where your site is, there could also be heritage reports, ground contamination reports and archaeological investigations.

Local validation requirements will tell you what you need to submit

Local validation requirements supplement the national validation list, with what the local authority considers as appropriate for their area. It tells you what information you need to provide with your application when you submit it. Once you have submitted all the required information on the Planning Portal, and paid your fee, you wait for the council to validate it.

There are two routes to a planning decision

If there haven't been objections to the scheme, or if they've been addressed and the case officer is satisfied, then there are two routes to planning approval that might be taken. The first is their delegated decision, which tends to be on smaller, non-contentious schemes. This is where the officer has been given the power to grant or refuse planning consent.

The other route is where it is put forward to a committee. This might be because it has been called in by a local councillor, or because it is more contentious with a number of objections.

You have six months to appeal a decision

If the case officer or committee refuse the application, you have six months in which to appeal. There are three routes for this.

The first is called written representations, which is the easiest and cheapest. In your statement you would set out your case and submit it to the planning inspectorate. The council does the same. The planning inspectorate reviews both statements and makes a decision as to whether the appeal should be allowed or dismissed.

The second route is a hearing. Both sides set out their case as above, but then attend a hearing together in person. The planning inspectorate will listen to both parties before making their decision.

And thirdly, it can go to a public inquiry. This is the most expensive and time-consuming and is run very much like a trial. There are barristers and witnesses, and the inspector will sit as judge. They make their decision based on the written evidence and what they've heard in the cross-examinations.

Choose a planning consultant based on their relevant experience

If you're looking for a planning consultant to work on your case with you, it is sensible to choose one with relevant experience of the appeals process that you are using. They should be a member of the Royal Town Planning Institute (MRTPI) and have a good track record locally. Don't be afraid to ask for examples of cases they've won, so that you know you're going with someone who is familiar with local policy and has relationships with councillors and officers in the area.

Councils have a statutory duty to make self build land available

Putting your name on the Right to Build register means that the council has a legal duty under the Self-build and Custom Housebuilding Act to issue the same number of permissions as there are names on the register.

Andy has been involved in appeals where they have been able to argue that because the council have failed in their legal duty to issue enough consents for self and custom building, then land which might be outside of settlement limits should be permitted for development.

Andy has also found that although some councils claim to have met their obligations by granting the same number of single dwelling permissions as there are people on their register looking for a plot, further investigation shows that actually, the majority of them aren't for self or custom build at all. Some of these can be planning permissions for up to 9 dwellings, where they're clearly developer-led models with no ability for customisation.

Self Build and Custom Housebuilding Supply in Braintree

8 out of 10 people aren't aware of the Right to Build Register

In one appeal that Andy worked on, although the council had met its obligations, they were able to argue that secondary data sources showed the register was actually a massive underestimation of the numbers of people in the area that wanted to self-build. Many of these were people that weren't even aware of the self-build register. The inspector in that case allowed the appeal, even though the council had met its statutory duty.

Andy would encourage anyone to add their details to this register though, as this will increase the number of self build plots the council legally has to make available.

Outline planning permission is less risky

A full planning permission provides all the details about your scheme, including layouts, landscaping, scale and massing. If you were to then get planning consent, all you would have to do is discharge the conditions against it, such as material samples, working hours on site etc.

What a lot of people do is seek an outline consent with access only. This is an illustrative plan showing what you intend to put on the site. With outline approval you have to get subsequent reserved matters approvals for all the elements that you haven't included at that stage. Outline permission is cheaper, so is therefore considered less of a risk.

Andy stresses the importance of discharging any pre-commencement conditions, prior to starting work on site.

Self builders can apply for CIL exemption

CIL is the Community Infrastructure Levy that some councils have implemented. It is a per square metre charge on development and is intended to pay for strategic infrastructure. Self builders can apply for an exemption, but it is incredibly important to follow the process correctly, and within the timeframes, as failure to do so could lead to a bill running into thousands of pounds.

Find out more

Visit the website of Tetlow King Planning

Follow Tetlow King Planning on Twitter

Transcript

Download a transcript of the interview with Andy Moger

HPH329 : What does a structural engineer do? – with Beth Williams

March 15, 2023 by Lucy Cowell Leave a Comment

Beth Williams from Build Collective outlines the role of a structural engineer and explains what tasks might be undertaken on a house build.

Interview with Beth Williams

Beth had wanted to be an architect since she was a teenager, and graduated from university with a degree in architecture and structural engineering. However, at the time she graduated, the UK was in the grip of a recession and the only job opportunities she found were in structural engineering. Part of the reason she has since gone on to work in the low-energy space, is that she enjoys the close working relationship with the design team.

Beth is a Chartered Civil Engineer and Certified Passivhaus Designer. She is an associate at Build Collective; a bespoke engineering consultancy in Bristol.

Structural engineering is a sub-discipline of civil engineering

Civil engineering sits at the top of the hierarchy. It covers things like highways and drainage.

Structural engineering is a specialism within that, but can still be quite broad. Structures can mean a focus on things like bridges and masts, or it can be for buildings.

So if you're looking for a structural engineer for your project, you can either opt for a chartered civil engineer (with a specialism in structures), or a chartered structural engineer. Beth explains that there isn't really any difference in terms of insurances and liabilities. The qualifications to look for are: the MICE (Chartered Member of the Institute of Civil Engineers), and the MIStructE (Chartered Member of the Institute of Structural Engineers).

They work as designers, under the principal designer

If there is no architect on the project, such as for a small domestic knock-through, then the structural engineer may take on the required role of principal designer looking after health and safety.

For most other projects though, the architect is the principal designer. They coordinate the flows of information between the design team members, and produce a pre-construction pack. That is all of the information from all of the designers, and all the health and safety risks. This is then passed on to the principal contractor to take as their responsibility once the construction phase gets underway.

Small projects might not need a structural engineer

If you are redecorating or moving an internal wall that isn't structural then you probably don't need a structural engineer.

Part A of the Building Regulations gives a generic outline of the structural principles, which could be used by an architect to design a very limited building such as a garage or an extremely basic house.

It used to be the case that people doing architectural work would have cover in their professional indemnity insurance for designing small structures. However, since Grenfell and a number of basement collapses in London, a lot of them have lost those insurances so the work has come back to the structural engineers.

Domestic clients will usually pay a fixed fee

Larger projects tend to be costed up on a percentage basis, whereas domestic clients are likely to pay a fixed fee for the defined scope of works. Beth's advice is to always check what is on the scope of works, and the number of passes included.

A lot of engineers base their fee on responding to a set of drawings once. Build Collective however, do a two-stage pass. This involves some rough sizing and layouts as a preliminary design. The architect uses that to develop their details before returning to the structural engineer for their detailed design. Having that extra pass allows for tweaks to be made based on new knowledge that might be acquired during the process, such as ground conditions for foundations.

Many factors impact on the structural system

Corner windows, fancy overhanging roofs, and flat roofs are just a few elements that will impact the structural system. This all feeds into the “Have I got enough wall?” question, which is for the structural engineer to answer. Things like large glazing and an open plan design will all obviously limit the amount of wall that they have. So it's about how much wall there is to make the structure stand up, and evenly distributing it throughout the building. Large stair openings and double-height voids mean there is less floor area to be able to distribute the loads.

Where there aren't walls, it might mean putting in portal frames or goalpost frames to give stability.

It's not just the vertical loads that need to be considered either. They also need to factor in whether the walls can withstand the horizontal load when wind is blowing on them.

Local structural engineers may have better knowledge of ground conditions

One advantage of hiring a local structural engineer is that they will be familiar with the area and its challenges.

For example Beth says that there are many cheap building plots in Bath because the ground conditions are often horrendous. It has a lot of historic landslip material that is volatile to work on. And Bristol has lots of coal mining areas and slope stability issues that will prove challenging.

Beth suggests a good use of money would be to pay a structural engineer for a few hours to look at geographical maps for your site and provide advice.

She would also recommend having a proper geotechnical survey for a new build, which costs around £3,500-£5,000. This involves a specialist geotechnical engineer doing bore holes or trial pits. They will log the findings and send samples away for lab testing, and report on the different structural and chemical properties of the ground.

If you can get a good ground investigation early on, you mitigate a lot of potential risks that could occur later on.

Your foundations will depend on your ground conditions

There is a range of sizes of ground particles, from large rocks down to gravels, sands, and clays.

Rock – For rock at depth, you might be able to pile down onto it, and lock onto the top surfaces
Gravel – Can be very flexible and have good bearing capacity
Sand – These can be good because they don't have the same volume change potential you get in clays
Clay – Clay heave can be an issue. The clay will swell and shrink over the seasons as it takes on more or less water. To get around that, you dig deeper to where the clay isn't affected by the heave. That may then be too deep to dig safely, so would need piling

Concrete may be something that you're keen to avoid but it does have its place.

Beth uses a lot of insulated raft slabs on low energy projects. It's a good solution for timber frame projects because you need some weight in the building to hold it down. If you are going to use concrete the important thing is to use it efficiently.

Another foundation option could be screw piles. They have some tension capacity in order to do the uplift for a timber frame. However, they're not going to be possible in every scenario, and Beth warns against clients fixating on them before knowing whether their ground conditions will be suitable.

(AECB members can access a webinar recording of Beth discussing alternatives to concrete foundations.)

The design starts with the roof

Beth uses a top-down approach, starting with the roof design. This is followed by any suspended floors, then the walls and lintels in the walls.

Even before she does these vertical load takedowns, she will look at overall stability. This incorporates the wind and snow loads.

A surprising level of information is needed to do the structural design

There are lots of things that feed into the structural design that may not be immediately obvious.

Staircases are a good example. Where there's a stair opening going up through the floors there needs to be a stair trimmer. There may also be a balustrade to prevent falls. What that balustrade is made out of will impact the structure. Glass obviously has more significant limitations on the deflection it can take before it cracks, than a lot of other materials. It has different fixing requirements too. Another consideration is how the balustrades for the stair itself join onto the rest of the balustrade.

When clients arrive with a specific product that they want to use, Beth sources all the data from the supplier in order to do the design. She has developed her foreign language skills because often the technical information isn't supplied in English!

Don't be afraid to involve an engineer early on!

This is especially the case if there is a specific product or system that you want to use. Get advice early to see how that might impact what the structure looks like, where the windows might go, and how many walls you might need inside. Beth would then do preliminary rough structural layout markups, ahead of planning, to show where the beams and frames could go. The architect can feed this back into their designs.

Find out more

Visit the website of Build Collective

Follow Beth Williams on Twitter

Transcript

Download a transcript of the interview with Beth Williams

Calling future engineers

Water expert Cath Hassell has featured on the podcast several times before (discussing topics such as saving water, rainwater harvesting and dealing with sewage). However she is also the creator of the Frankie the Flamingo series of books for children. So if you have a budding engineer on your hands perhaps The Mysterious Case of the Elephant that Forgot is a good place to start.

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HPH326 : Is it worth upskilling your knowledge of Passivhaus? – with Simon Bell

February 1, 2023 by Lucy Cowell Leave a Comment

Landscape Architect and Director of HLM Architects, Simon Bell, explains why he decided to upskill when it came to building his own house.

Interview with Simon Bell

HLM Architects are an award-winning practice with offices in England, Ireland, Scotland and Wales. As a Director, Simon was familiar with one of the projects designed from their Glasgow studio – Tigh na Croit – and knew that he wanted the same architect (Ross Barrett, who is also a friend of his) to design his own home.

A Passivhaus doesn't need to be a simple box

Something that Ross proved with the L-shaped design of Tigh na Croit, is that a Passivhaus doesn't have to take on the simplest form. Yes, it can be at its most efficient as a straightforward box, but it is also possible to create buildings with architectural merit and beauty as well, it just might take a bit more effort to make the standard work.

The panoramic beauty of the site created Passivhaus challenges

Based in the centre of Northern Ireland, the stunning site is near a small village called Broughshane, close to Ballymena. They are up in the hills, with fantastic views to the east and west, and also panoramic views to the south. This meant they were always going to be faced with the challenge of balancing those out with solar gain, shading and window ratios, and is why they now have framed views of the landscape, rather than a huge expanse of panoramic glass.

The value of an architect is to bring a different vision

Having given Ross a brief around how they wanted to live in and use the house, it naturally lended itself to a long house type arrangement, which would have been far simpler from a Passivhaus perspective. With further design iterations they found that it wasn't quite going to work as they would like. Ross then presented a new design where the walls weren't parallel. It widened out as it got to the centre of the house, and then narrowed down at the ends. This was the design they decided to move forward with.

He wanted to be an informed client

Being the kind of person that likes to learn and understand how things work, and know the right questions to ask, when it came to the design and build of his own Passivhaus Simon was keen to develop his knowledge further. He took inspiration from Tomas O'Leary who had a similar background as a landscape architect, and has gone on to be internationally respected in Passivhaus circles with MosArt. This gave him the confidence to take on the Passivhaus Designer course himself, which he found to be intense and challenging, but also appealed to him with its methodical processes and attention to detail. Doing the course at the same time as working on the final stages of his own house design, meant that he was able to experiment in PHPP and take a lot more time to test things out for himself and understand the impacts that various changes made.

Quality control and education became part of his on-site role

In resisting his desire to be a hands-on self-builder (which he accepted fairly early on was going to be unrealistic if they wanted to be living in a house within 5 years!) Simon decided he wanted to take on the role of informed client, and work very closely with everyone on the team. Building through covid restrictions meant that he took on much more of the site role, as Ross wasn't able to be present as often as he would have liked. Simon was able to educate everyone that came to work on the site about Passivhaus, and how things that seemed insignificant would actually be important to the overall performance of the finished building.

Contractor attitude was more important than Passivhaus experience

When it came to selecting a main contractor, they found that there was a very limited number that had Passivhaus experience. Instead, they focused on their attitude, attention to detail on other builds, and evidence of where they had gone above and beyond building regs before.

They established a no-blame culture

Due to the pandemic restrictions, Simon ended up being more hands-on that he had originally intended. Living nearby meant that he could visit the site daily and be there to highlight issues or anything that needed particular care. This included setting up a no-blame culture, so that if anything was damaged they would all be informed, affording the opportunity to rectify it, rather than having it covered up and becoming a bigger problem later on. The contractor responded well to this and had come into the project wanting to learn and understand, and deliver it to the best of their ability.

Having a live project helped his understanding of the course

Even with the Passivhaus training course, Simon found that so many things you just have to learn about on the job. This was true for him particularly around the detailing, and finding the optimum solution for a heating system.

Trust in your consultants

Although it isn't necessary for clients to take the Passivhaus training course that Simon did, he does recommend that they do some reading to get a good understanding of the standard and how it works. The Passivhaus Trust has plenty of guidance available which is ideal for this and is pitched at different levels. Simon also believes that it's important to put your trust in your consultants too, and give them a degree of freedom to come up with the solution.

“Perhaps not get too involved in some aspects and more involved in focusing on how they're going to use the building and communicating that, but not necessarily getting too hung up on the actual technical solutions.”

The pandemic presented the biggest challenges

The main concern for them was getting the required level of airtightness, but the Covid pandemic brought about the greatest challenges. It impacted on materials, getting people to site, and causing delays and knock-on effects to the programme. It left the structure open for longer than they would have liked, which again had further implications.

Each build presents a learning opportunity

It's about good design, good practice and attention to detail. Simon's advice is to embrace upskilling and have the confidence to do it, whether you're a client, designer or contractor. And when a project has been delivered, go back and review what could have been done better, and what do you need to upskill in the future.

“It's a continuous process. We're always learning, we always need to learn, and that should be the mindset rather than trying to maintain a status quo where we always do things the way we've always done them. Let's challenge ourselves to always improve and do better.”

Find out more

Visit the website of HLM Architects

Follow HLM Architects on Twitter

Transcript

Download a transcript of the interview with Simon Bell

Video of HLM's Tigh na Croit

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HPH325 : What reduces the performance of insulation? – with Mark Siddall

January 18, 2023 by Ben Leave a Comment

Mark Siddall explains how thermal bypass – or air movement around insulation layers – might impact a self-build or retrofit project.

Interview with Mark Siddall

Mark is a Passivhaus specialist who has been on the podcast before, talking about avoiding the risks of poor ventilation and his ‘forever home lifestyle’ framework.

His practice LEAP operates from County Durham and Newcastle. He is also a technical adviser to the Passivhaus Trust and the AECB. He has written a paper on thermal bypass risks for the Passivhaus Trust.

There are many types of performance gap – but energy is often the focus

For Passivhaus buildings, the focus tends to be energy performance rather than other factors like air quality. Passivhaus projects actually close gaps in predicted performance, which can’t be said for other approaches. The methodology has got better quality assurance processes, which avoids risks that might otherwise arise.

Insulation has to be specified correctly for it to deliver energy performance benefits

Dealing with energy performance often means the thermal performance of the building fabric. Three variables influence whether insulation works or not.

The material itself.
Whether the material is specified sympathetically for the construction method used.
Whether the material is installed properly.

Get those variables aligned and the evidence shows everything works properly.

An example of an air gap when using blockwork and rigid PIR insulation

Choosing insulation for cavity walls

Cavity wall construction is very common in the UK. A Passivhaus designer will question if the usual foam insulation solution is sympathetic to the method of construction.

Blockwork features mortar joints, and mortar is squeezed during installation. That creates snots which project into the cavity and stop the insulation sitting against the face of the blockwork. The resulting small air gap is enough to completely undermine the thermal performance of the insulation.

Mortar snots can be cleaned off, but that might not happen all the time. A mineral wool solution is more flexible and capable of dealing with subtle deviations, so it’s a more appropriate insulation for a cavity wall. It’s also used to the full depth of the cavity, which helps to reduce the risk of air movement.

Mineral wool fully filled cavity at Steel Farm Passivhaus

Airtightness is about moisture as well as heat loss

Part L of the Building Regulations deals with heat loss and prescribes a specific level of airtightness. Part C talks about moisture and only says things should be fairly airtight. There’s no numerical target related to moisture, and that’s a problem.

The Passivhaus standard, and research conducted in Canada, both confirm that airtightness of 0.5 or 0.6 air changes per hour at 50 Pascals is needed to avoid damage to timber structures (such as roofs or framed walls). That’s an air permeability of around 0.5, compared to the Part L target of 8.0.

Good airtightness alone doesn’t guarantee insulation performance

From the external side of the wall, wind tightness stops the wind blowing through and around the insulation, which wicks away heat. It’s not something that can be tested on site, however. As a rule of thumb, the quality of workmanship needed for a wind tight layer is similar to that needed for the airtight layer.

Fully encapsulate insulation between the air and wind barriers

Convective loops can happen around insulation just from the temperature differences between the warm and cold sides of the wall. We can avoid that by properly encapsulating the insulation between a notional air barrier and wind barrier.

Using the same cavity wall example as before, a good build-up might be brickwork or stonework on the outside face. Then a 300mm cavity full filled with mineral wool insulation that's built up in two or three layers. The inner leaf is blockwork, which is plastered internally.

The plaster acts as the air barrier, and the brick or stone is the wind barrier. The cavity is fully filled, so the insulation is encapsulated and has no air gaps around it.

Rainwater is the dominant moisture problem to tackle

Cavities were introduced to walls to act as a capillary break and stop water being drawn through from the outside. Any water getting through the outer leaf drained down the inside face of the cavity and out through a weep hole.

A very narrow cavity fully filled with insulation carries a risk of rainwater bridging across to the inside of the building. That risk reduces with a wider cavity. Passivhaus design requires wide cavities and, with good workmanship and no mortar snots, any risk from driven rainwater is mitigated.

Installing the cavity insulation in layers means that if any water gets through one layer, it can still be pushed down and back towards the outside.

Think about how wall ties affect performance too

Cavity wall ties help to provide structural stability, but are also a repeating thermal bridge through the insulation layer. Mark specifies Teplo wall ties instead of stainless steel ones. Stainless steel ties have a larger physical dimension and a higher conductivity, whereas Teplo ties are thermally broken.

Design calculations usually assume perfect installation

On most projects, architects contact insulation manufacturers for U-value calculations. The manufacturer never asks what quality of workmanship is being specified. Instead, they assume perfect installation, which requires certain tolerances on site.

When those tolerances aren’t achieved and workmanship is less than perfect, which is the case on every building site, then air gaps are the result. Materials haven’t been specified to work sympathetically with one another and the predicted U-value isn’t achieved.

Timber frame construction can help to address performance gaps

From inside to outside, a typical timber frame construction capable of producing good results would be:

Plasterboard.
Service void, which may or may not be insulated (ideally not).
Airtight layer.
Engineered I-beam filled with cellulose insulation.
Wood fibre insulation on the outside.
Wind barrier membrane.
Drained cavity, acting as a capillary break.
Rain screen on the outside face.

Compared to this build-up, performance gaps can occur because standard industry timber frames don't have the wood fibre layer, don’t use engineered I-beams, and are less likely to feature a service void. Services penetrating the air barrier will allow moisture from inside the house to get into the timber frame, potentially causing moisture damage.

One area they tend to do well in is using 150mm thick insulation in the 140mm frame. Because the insulation is that little bit bigger, it’s compressed slightly and ends up being snugly sandwiched between the air barrier and wind barrier. There’s less risk of convective loops.

Improvements can always be made to reduce performance gaps

Research from places like Sweden and Canada is showing that, in the construction described above, moving the wind barrier behind the wood fibre (which might be just 20mm thick) could significantly reduce the risk of condensation.

The climates are different to the UK, so the conclusion might not be the same here, but it shows there are still refinements that can be done in Passivhaus timber construction to make it even more resilient than it already is.

Air movement is the issue across all build systems

All construction technologies need to address the key issues of building physics. With straw bale, for example, a lime or clay plaster on the inside can provide the airtight layer. There are other subtleties and complexities, but it’s a case of limiting air movement through, and within, the wall construction so the building performs as predicted.

An example of a warm roof (Shepherd's Barn)

The same principles apply to roofs…

…although it depends what type of roof it is. A warm roof construction is very similar to the timber frame walls, just at an angle. The tiles or other roof covering replaces the rain screen.

A cold roof, with insulation at ceiling level and the attic space above is risky to deal with from a moisture perspective. Information Mark has seen suggests one-third of the moisture that transfers into the roof space could condense on the roof structure. It has to be possible to remove that, using a vapour permeable underlay.

Ventilation can also be used, but there are reasons why that may or may not be preferable or doable. Then it’s necessary to look at the eaves detail and the risk of wind washing. Air comes into the loft at higher speed, so special details are needed to help protect the insulation at the edges.

The important advice is to keep things simple

Details have to be simple to make them buildable. Then they can be replicated from person to person, site to site, and house to house.

Make sure you have an air barrier and a wind barrier, and that you encapsulate the insulation. Do that and you’re on the right path.

The ‘Thermal Bypass Risks’ paper on the Passivhaus Trust website provides solutions. It includes tips and tricks for designers and architects to help mitigate thermal bypass. Each section features accessible takeaways that could also be used by self-builders.

Find out more

Visit the website of LEAP

Follow Mark Siddall on Twitter

Read Mark Siddall's paper on Thermal Bypass Risks

Watch the documentary case studies at PassivhausSecrets.co.uk

Transcript

Transcript-of-House-Planning-Help-podcast-episode-325-Mark-Siddall

Dear Evil Engineer

Thank you to Stephen Miller in Oxford for sharing this with us. The Institution of Engineering and Technology has a bit of fun from time to time with their Dear Evil Engineer series. Villians write in for advice on their diabolical plans.

So how many leopards do I need to heat my home? And they even consider homes that are built to Passivhaus standard!

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HPH319 : Natural materials and healthy homes – with Tom Woolley

July 22, 2022 by Lucy Cowell Leave a Comment

Architect, educator and builder, Tom Woolley, takes us through some of the natural construction materials we should be using to build healthier homes.

Interview with Tom Woolley

Tom is a returning guest to the podcast, with hempcrete being the subject of his previous interview.

Now, he has a new book: Natural Building Techniques – A Guide to Ecological Methods and Materials, and it is topics within that which we have been discussing with him. His book includes sections about renovating and retrofitting, information about suppliers, and different kinds of natural materials that are available. It also looks at some recent case studies, talks about how to tackle projects, and what some of the obstacles might be that you could come up against.

The supply chain of natural materials is becoming far more robust

Tom explains that for a long time people have been given excuses about why natural materials are too expensive or don't work, which has acted as a barrier to their take-up.

However, in recent years, a lot of work has been done to make the supply chains more robust, with greater availability and, in some cases, cheaper pricing. This in turn has encouraged more people to try them.

Tom also believes that new fire and thermal performance regulations will make it harder for plastic and synthetic insulation companies to fabricate results, and composite materials like hempcrete will be shown to be just as good.

The term that is generally used for natural materials is bio-based materials, which covers anything from timber and straw, to hemp, sheep's wool, and other natural fibres. Closely linked are also things like earth and lime.

We need to stop using timber carelessly

When it comes to the sustainability of using natural products, Tom addresses the current problems with timber.

“There's enormous amount of wastage of timber really. Timber is used in many situations, where it probably isn't needed to the extent that it is, but people just chuck it in as though it's a cheap material, which it no longer is.”

He also says that there is a lot of misinformation around the flammability of cross-laminated or mass timber construction, which has resulted in people returning to use concrete.

We do though need to be careful and responsible in our use of timber, and Tom explains that there are companies in the UK that are constructing using locally harvested roundwood poles, which is a great way of using timber more responsibly and economically.

Tom also suggests that there are many more resources that remain untapped, for example the biomass waste from palm oil trees could be used for bio-based composite products.

Lime and clay can be great alternatives to cement

Tom has been working with lime for a number of years and says that it is a natural biocide which is very good for healthy buildings. It does however still use energy to produce it, so he is now experimenting with a clay powder that seems to work almost the same as the lime, and which would save a great amount of embodied energy.

Stone and earth are two of the oldest forms of building material

Stone is a natural material that can be re-used and Tom is horrified when he sees sites being bulldozed and the stone being buried, when there are far greater benefits with the many other ways it could be used.

While cob and rammed earth have plenty of advocates, using these materials alone it can be hard to reach modern standards of energy efficiency. However, they are hygroscopic and have health-giving properties that make them a very good material to use.

Tom is a great believer in hybrid construction these days, and building with timber, sheep wool, earth, hemp and all sorts of other things, depending on what's available and how they can be combined together.

Straw can be tricky if you don't know what you're doing!

Tom admits that he's not the biggest fan of using straw as a construction material, largely because he's seen so many straw bale disasters!

People often think because straw bales are relatively inexpensive, then it must be cheap to build a straw bale house and anyone can do it. However, there are a number of pitfalls, such as when you have a roof resting on the walls you need to factor in that bales are going to move, their suitability in very wet conditions, and having to be extremely well rendered and plastered to make them safe from fire.

He has however seen some wonderful examples, particularly when the straw bales are used as infill within a timber frame, rather than being load-bearing.

If you are looking to build with straw, Tom recommends getting experience first on another project so that you know what's involved, and preferably attend a training course run by experts.

Hempcrete is an excellent material for managing moisture in a building

This would always be Tom's preferred method of building, used as 300-350mm walls within a timber frame construction. It has an impressive thermal performance and also creates a very healthy environment because of its hygroscopic properties.

Over the last year, they have had a study done by the University of Ulster on one of their hempcrete buildings. Despite temperature and humidity levels varying greatly throughout that time, the relative humidity stayed exactly the same.

It is also very versatile in its application. It can be mixed in a mixer and cast in shuttering, it can be sprayed into a building, and it can also come in block form.

Hemp is readily available for use in construction, with more growers jumping on the bandwagon of bio-based materials for company carbon off-setting. It is a useful crop for farmers because it's used in the annual rotational cycle between cereal crops such as barley and wheat. The fibre is stripped from the hemp and this in itself becomes extremely valuable. The hemp fibre can be used in a variety of insulation products or composites, including car interiors and replacing plastic in aeroplanes.

Emphasising eco-credentials can make mortgaging more challenging

Tom thinks that sometimes approaching insurers, mortgage providers, planners, and building control professing your wacky eco house ideas can be detrimental!

He suggests that by being more tactical and not making a song or dance about it, you're less likely to have a problem. He gives the example of a small company in Wales who have just sold a trial hempcrete house, which got a mortgage from Nationwide Building Society without them batting an eyelid.

“It's no good just saying, Let's insulate it”

With his book, Tom is keen to educate even some of the green movement who emphasise the importance of insulating all the buildings in Britain, while effectively promoting the use of petrochemical insulation materials.

“There must be lots of white van men out there just happy to come and stick any sort of plastic rubbish into buildings. That is not good enough. We have to get people to use the right materials and the right techniques that aren't going to damage the planet and aren't going to damage people's health.”

He accepts that there will always be some things that can't really be made out of anything other than plastic, and if they're used in a sparing and limited way then that's something that shouldn't be condemned. However, he takes issue with some of the Passivhaus organisations for promoting materials that are plastic and synthetic oil based, which they are claiming will help to save the planet by reducing energy. When 50% of the plastic waste going into the oceans is from the construction industry, Tom questions why they need to be wrapping buildings in plastic membranes, when we can build airtight buildings with hempcrete that are fully breathable and aren't wrapped in plastic.

Active House provides an alternative to Passivhaus

Tom sees Active House as having a more holistic and sensible approach to these issues, particularly around the design and configuration of buildings, use of daylight, passive solar etc. The Active House Alliance has recently been set up in the UK and certification will be offered in the future.

We don't have enough building performance data

Tom is keen to see far greater investment in building/material performance data, but says that while organisations such as Innovate UK have thrown money at petrochemical solutions, they haven't been as supportive of natural and bio-based approaches.

There are however some very good centres of research that are being set up, such as at the University of Suffolk. Tom has also been in discussion with Cardiff University about doing some testing on further hempcrete houses that are being built in Wales.

“We know that they work, but it's no good having the anecdotal information that we know that they work really well, and even better than synthetic materials. We need to have the hard facts, we need to have the data. And we also need to have more standards.”

Research in the UK and around the world shows that issues around mould are another big challenge that needs to be faced, even for properties that have been renovated. But there are now many in the medical community that are recognising the environmental causes of health problems, such as VOCs, formaldehyde etc. Tom sees natural materials as being the solution to get out of these problems, and this is likely to be one of the main directions of his work in the coming years.

Find out more

Visit the website of Rachel Bevan Architects

Find out more about Natural Building Techniques: A Guide to Ecological Methods and Materials

Transcript

Download a transcript of the interview with Tom Woolley

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HPH318 : Do I need a structural warranty for my self build home? – with Jake Fitness

June 27, 2022 by Lucy Cowell Leave a Comment

Jake Fitness of Self Build Zone explains what a structural warranty is, and why you might need one on your self build or renovation project.

Interview with Jake Fitness

Jake Fitness is a team leader at Self Build Zone, a provider of site insurance and structural warranties.

A structural warranty is a type of insurance policy

It can cover any new structural works you do on a project, whether it be a new build, renovation or extension.

It will be more costly to add on at the end

Jake stresses that the ideal time to start thinking about the structural warranty is when you have a pretty good idea of what your project will entail. This is for three reasons:

To ensure that your building is acceptable to warranty providers
To be able to factor it into your project budget
Leaving it until the end will mean they charge a higher price, as the surveyor won't have had full visibility of the build process.

“If you're thinking about doing a project anytime soon, really make it one of the first things you do, because it's more important than your kitchen, your doors and your windows and all of the nice looking fittings, because ultimately, it's what's going to pay you if there is something wrong with your build.”

Typically the price of a warranty is based on the size of the property, the frame construction type, and the build cost. The average warranty cost is between £2,500 and £4,000. This covers the full premium for the 10 years, plus all the site audit visits.

It isn't a legal requirement

It is however likely to be a lender requirement if you're looking to re-mortgage the property within that first 10 years, or if you are going to sell it during that time. You can still purchase a warranty at that time, but you will end up paying a far higher price for it.

It doesn't hold anyone liable for the damage

The difference between a warranty and a standard contractor's guarantee, is that you don't have to hold anyone liable for the damage that has been caused. This is because rather than blame being placed on the architect or contractor for cracks etc, the warranty provider will conduct an independent survey to assess the damage and pay you for that loss. This can be beneficial if you're looking to sustain the working relationship with the team in the future as you're not trying to place blame on an individual or company that may not even be at fault.

Technical audit surveys are carried out

These repeat visits are similar to that carried out by a building control officer, but are purely from the viewpoint of whether there is likely to be a claim within the next 10 years. They are more comprehensive than whether they just meet building regulations, and on a new build would typically take place:

when the foundations are fully excavated but before the concrete is poured
at the damp proof course stage
for brick and block it will be when you're at first floor joists, or for timber frame and ICF it will be when the frame has been erected

“We'll still carry on even when you're at the weathertight level all the way up till completion, letting us know of any defects during the build, which, to be honest, most builders if they've built a small defect in then they're probably going to not let you know about it. But we will stop the building in its tracks if we need to, just to make sure everything's rectified and built to a very good standard.”

A structural warranty will cover defective design, workmanship and materials

This will be for a period of 10 years after completion.

An example of this could be the structural engineer not designing the foundations deep enough and the property subsides. Worst case scenario would be a claim for completing demolishing and rebuilding.

Other things that would be picked up could be things like a roof not being designed to take the full weight of solar panels, or poor mortar mixture being used that needs remedying.

Select a provider that has an A rating

Although the actual cover of the warranty is much the same for all providers, it is important to check that who is actually insuring and paying for the claims has an A rated backing. This relates to how financially stable they are, and how likely they are to still be around in 10 years time if you do need to make a claim.

Jake says an unrated insurer should be avoided as they don't have evidence of their stability within the market.

He also recommends doing your due diligence by checking out blogs, reviews and testimonials to select your provider.

All construction types can be covered

Jake explains that Self Build Zone will cover all construction types, because each self build is so different. Rather than making blanket statements about the construction types they are able to rely on the auditing process from when they come out to do the inspections. This includes straw bale with thatched roof, and green oak frames.

Having been a warranty provider for over 20 years, Jake says that they are helped by being in the position of knowing what causes claims within the 10 year period, and the types of risks associated with each construction type.

A structural warranty is more comprehensive than alternatives

Contractors have a defects period where they will be responsible for all claims for the first two years following completion. That's not something that you would typically have under a self build warranty though, as self build can relate to anything from full involvement by the contractor, right up to 100% of the work being done by the homeowner themself. If you do rely on a contractor's guarantee and they go out of business within the following 10 years, you won't have anyone to go back to for any of the defects that may arise.

Likewise, architect's certificates (Professional Consultancy Certificates) are also sometimes available, but will only cover defective design, and not the workmanship or materials for the property. You would also have to prove that the architect was at fault, and are usually only valid for six years. In contrast, with the structural warranty, you don't have to evidence the fault to any particular party to claim, and it would be provided for 10 years.

Another reason for having a structural warranty, is that sometimes local authorities may ask for one to show that your property is a self build and therefore exempt from paying a community infrastructure levy.

Find out more

Visit the website of Self Build Zone

Follow Self Build Zone on Twitter

Transcript

Download a transcript of the interview with Jake Fitness

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Subscribe, rate and review us on Apple Podcasts

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HPH315 : Simplifying the delivery of high performance, sustainable homes – with Mike Jacob

May 11, 2022 by Lucy Cowell Leave a Comment

Mike Jacob explains how Kiss House is using timber component based production to deliver homes to the Passivhaus standard.

Interview with Mike Jacob

Mike Jacob's journey from project manager of quirky conversions and renovations to co-founder and director of Kiss House happened organically, and stemmed from his ongoing desire to do things in a better way. He continued developing his education and qualifications, learning more about sustainable architecture at the Centre for Alternative Technology, and working for a Passivhaus startup.

Kiss House “brought itself into being”

After a decade spent delivering one-off, complex housing projects, Mike and his colleagues felt that there must be an easier way of transferring their lessons learned into a vehicle that could benefit more people, rather than starting from scratch each time. In doing so, they saw the benefit of scaling up a business that had a repeatable housing product, which felt like it had been individually designed, but without the risk, uncertainty, and stress that often goes along with that.

A bespoke house that a colleague had designed for a private client, started to get enquiries because people thought it was a configurable, repeatable house. This kickstarted their thinking that this could be their vehicle for transferring their lessons learned, and began exclusively working on Kiss House.

It was important for their designs to have an identity

The Kiss House design is a contemporary, cuboid, minimal piece of architecture, drawing on their previous experiences and inspired by landmark projects from the 20th century, to offer more of a mass customisation approach to housing. Although the company is still in its relative infancy, as they develop new housing types they intend to stay within a kind of aesthetic language, being contemporary in nature.

The custom build style alleviates many of the risks

In Mike's experience, many of the truly bespoke projects tend to come unstuck and have tensions for a number of reasons. Often this will happen when trying to incorporate high levels of energy efficiency, and can either end up with compromises on the architecture or the performance.

The Kiss approach aims to be a simple, stripped back, clean lines aesthetic, with uncompromising performance. It can be configurable to an extent, but is ideally suited to a custom build market. Moving forward, they will be building a portfolio of individual Kiss houses that all have commonalities, and beyond that they're having conversations with local authorities and developers who are interested in different typologies, all recognisably Kiss, for delivery of housing at scale.

Each house will be built to the Passivhaus standard

Together with developing their system, they have developed the architectural language for that system which enables them to have a much more flexible kit of parts approach to housing typologies that are more site specific. They are also working hard to ensure that each house will be Passivhaus certified.

They will have their own manufacturing facility in the UK

Mike explains that by vertically integrating themselves with their manufacturing partners, they'll be able to de-risk the supply chain wherever they can. They'll be bringing as much in-house to their manufacturing facility as possible, including the manufacture of the triple glazed windows, to become a one-stop shop for their housing product. And by being more in control of their supply chain, they're able to offer a better service to their customers.

“We've tried to come up with something that addresses all of the pain points, or as many of the pain points as we believe are there, so that our customers maybe even enjoy the experience!”

The ambition is to use only UK grown timber

Currently, the only imported material they use is sheet timber, which they use sparingly and are trying to find workarounds for. They are trying to galvanise the domestic supply chain and are looking at ash and beech for things beyond the structure, such as for furniture and flooring.

Working with the Bio Composite Centre at Bangor University for the last couple of years, Kiss House are also looking to bring to market a UK manufactured natural fibre insulation.

The house is partially pre-fabricated off-site

The kit of parts is manufactured at their facility in the south of England, and is made up of two different types of columns, along with cassettes and panels of various shapes and sizes. They are manufactured digitally on a semi-automated basis and to high levels of precision. The components that leave the facility are insulated, and sometimes with internal lining boards and external cladding. These are then transported to site, where they are assembled without the need for a crane or scaffolding. A typical house would take just a few days on site before it's airtight/weathertight, and then a further 4-6 weeks for the fit-out stage.

The first house will be a demo

Mike explains that they're currently manufacturing their first house, which will be a demo house built at the factory. Their first live projects will be delivered on site as soon as they can get them through the planning system, where they've been experiencing horrendous delays.

It has taken plenty of perseverance to keep going against the odds!

Having lost around two years because of things like lockdown and planning delays, it has been a challenging journey to get to where they are today. However, they, and their patient investors, have kept faith and are at an exciting growth stage where they are joining forces with their manufacturing partner to embark on a new round of fundraising.

Find out more

Check out our previous podcast with Mike Jacob: Does Hiring a Project Manager Save Money?

Visit the website of Kiss House

Follow Kiss House on Twitter

Transcript

Download a transcript of the interview with Mike Jacob

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HPH314 : Getting a self build over the finish line, despite setbacks – with Mike Coe

April 13, 2022 by Lucy Cowell Leave a Comment

Mike Coe gives a final update on his now complete Portree Passivhaus, that has seen budgets stretched, contractors disappear for a year, and a Covid lockdown!

Interview with Mike Coe

Mike Coe is a returning guest to the podcast. We have been fortunate enough to speak with him about his previous self build, Cropthorne Autonomous House, and have been following his progress since moving to the Isle of Skye to build Portree Passivhaus with his partner Lizzie. Having been in the house for a year now, we pick up where we left off three years ago, in episode 259 when the house was almost watertight, and find out whether Mike has managed to be as hands-off with this project as he had intended!

Mike had always intended to do the MVHR installation and electrics himself

He had started on the MVHR installation as soon as there was enough building there for him to work on. The main ducts that bring the fresh air in and take the exhaust air out, went in almost at the foundation stage, as they were assembled as the wall was being built that the ducts pass through. This way it meant they could be built into the wall, rather than having to cut out a large hole afterwards. He also started channeling out for power points before the concrete blocks were even up to first floor level.

The specification of the MVHR was important for Mike as he wanted to build this house with no heating system whatsoever. They selected a system made by Nilan, which also contains a micro heat pump. It's only around 60 or 70 watts, but it effectively aids the heat extraction process and makes it more efficient. It means that in the winter the heat pump comes on when the temperatures dictate it, making the incoming air temperature slightly warmer, and in the summer it provides a very small amount of cooling.

Their only other source of heating is from a single bar electric fire which they've used infrequently, just for the odd hour here and there.

It maintains a comfortable temperature

The internal temperature on the night they moved in was just 11 degrees (with a raging storm and a power cut for good measure!) But once Mike got the MVHR up and running a couple of days later, and they had a week or two of sunshine, and with the effect of the two of them living there, it took just a couple of weeks for the temperature to rise to 21 degrees. Since then, they have been pleasantly surprised at how well it keeps a steady and comfortable temperature, even more so than the Cropthorne house, despite its larger form and having been less fastidious in the attention to Passivhaus detail. Mike suspects this is because of using the concrete blocks which, as well as providing the structure of the building, also act as a thermal store. He is conscious that the use of the concrete blocks and steel means it has higher CO2 emissions from the manufacture than that of a lightweight timber structure, but this was primarily dictated by the planning department.

Mike's previous Passivhaus experience paid off

With a contractor and architect that didn't have experience of building a Passivhaus, Mike found one of his roles on site being that of quality control. When it came to airtightness tape, he was able to show them how the standard builder's merchant tapes would just tear like paper, yet the Passivhaus airtightness tape was incredibly strong and flexible.

They didn't mind and were happy for Mike to take on other pieces of work, such as some of the carpentry, especially as he and Lizzie were on site doing the MVHR and electrics anyway, and it meant the workload for their men was reduced.

It took twice as long to build as planned

The original plan was for a 15 month contract build period, but at the 10 month stage the contractor got called away to work on a 25 bedroom hotel extension, leaving just Mike, Lizzie and a freelance bricklayer to carry on with the work. This meant an incredibly frustrating almost year-long wait while the hotel project was finished, which unfortunately then coincided with the first Covid lockdown.

“So there we were, with another three months added on to the almost year long delay due to the hotel build. The hotel extension was sitting there virtually complete, but they couldn't open it because of everything was shut down because of Covid, whereas our house was nowhere near complete and nobody could work on it except me.”

Mike managed to use that time as productively as possible to keep the project moving forward. Without being able to access new building materials as the merchants were closed, he dismantled some of the temporary stairwells that the contractor had put in so he could use the timber for building the stud partition walls. He used all the plasterboard that was laying around that he could, rescued timber that had been thrown out and used that for the stud walls, and also managed to build a new desk. Psychologically he found all this beneficial as it felt like progress was still being made.

In total, the project took around 30 months to complete.

Money became very tight

With the planning department selecting the most expensive option, they always knew that the budget was going to be tight. In addition to the overruns caused by the lockdown, a number of other bills came in that caused them to go over by £34,000. This included £8,000 to install a water pipe from the mains halfway up the hill, rather than being able to connect from the supply of the neighbouring bungalow that they owned and were living in, and £750 for a tree survey to make sure that the pipe wasn't going to damage any tree roots!

As they were running out of money and with cash being tied up in the neighbouring bungalow until it was sold, they had to take on more of the work than they had ever intended to do. Mike had been unimpressed with the plumber who had done the first fix, so ended up rectifying some of his work and also did the second fix plumbing. This meant he plumbed the washing machine, kitchen sink, dishwasher, and the fit-out of all the bathrooms.

With great reluctance, as it is a job he and Lizzie particularly dislike, they also ended up doing most of the decorating themselves.

One year on, there are problems to rectify

Having been in the house for a year, they are currently in the snagging period where the contractor will rectify some of the problems that crop up. Their contract allowed them to withhold a small percentage of the total payment, which will be paid once these have all been sorted. However, there are other problems which Mike intends to take on himself.

The door in the lower ground floor porch was never properly adjusted and would stick and not shut fully. When he got round to looking at why this was, Mike discovered that it was actually causing a serious damp problem. The damp had resulted in the hinges corroding, with the adjustment screws for the doors then being impossible to turn.

Something else that Mike will need to tackle, is an issue with the windows leaking. As they weren't a standard specification that the contractor was familiar with, they installed them but weren't confident to set them up, instead leaving this to Mike to organise. However, with all the other jobs and distractions going on, this got pushed lower down the list. With the driving rains they receive, several of the windows subsequently leak. Thankfully there are no serious structural leaks though, and when all the adjustments to doors and windows have been carried out then hopefully that should be an end to those problems.

During a period of extremely high winds recently, part of the zinc capping that goes around the roof parapet was torn off. Fortunately it doesn't threaten the structure of the house in any way and it's still watertight, but it's something else to add to the list of jobs.

He has some carbon-saving projects lined up

Now that they have freed up their cash by selling the neighbouring bungalow, and once Mike gets over a certain amount of self-builder fatigue, he is keen to make headway on some other projects.

The first is installing a PV array that will make the house run more efficiently, as it will contribute to hot water and charging their new electric vehicle.

He is also in the early planning stages of putting a micro hydro generator (a little water turbine) into a stream that runs down through their site. If it works it will likely only generate around 100-150 watts per day, but that will be for 24 hours a day and virtually through the whole of the year.

He is adamant this will be his last self build!

Now he and Lizzie are able to reflect on their journey, they are able to say that although lots of things went wrong, they managed to get them corrected. Although they did have the benefit of experience from their previous self build, there were still new problems that this project threw up that had to be dealt with. Overall, Mike says they are pretty happy with the end result, just not necessarily with how they got there.