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

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

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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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HPH259 : Constructing the masonry superstructure of Portree Passivhaus – with Mike Coe

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Mike Coe has a progress report from Portree Passivhaus, which is now almost watertight. We pick up the story as the groundworks begin and look at some of the challenges as the superstructure has gone up.

Mike Coe on the roof at Portree Passivhaus

Interview with Mike Coe

Mike Coe has been on the podcast a number of times. Our first interview with him was when he completed building the Cropthorne Autonomous House, where we imagined he might stay put for many years. However, with concerns over climate change, he and his partner Lizzie Stoodley decided to move further north to the Isle of Skye in Scotland.

This meant selling the autonomous house, which was not straightforward, and taking on a second project with well known architects Rural Design.

A section of Portree Passivhaus
A visualisation of the finished house

The sloping site was perfect for upside down living

Mike's previous house, the Cropthorne Autonomous House, had bedrooms downstairs, and the living space and kitchen upstairs. Mike prefers this layout and was keen to repeat it.

That's why one of the attractions of the site was its slope. The main entrance could be at the top of the house, taking you directly into the living space.

The dig begins
‘Rotten rock' is discovered

Rotten Rock provides a perfect base from which to build

Mike explains that whenever anyone builds on Skye they look for ‘rotten rock', which is a combination of the normal clay subsoil but with volcanic small rock particles mixed in. This makes a stable foundation that you can build straight onto.

Although they were digging into the hill, the rotten rock is almost solid enough to dispense with a retaining wall (but not quite!).

The Cropthorne Autonomous House

His first self build guided a lot of decisions

At the autonomous house the heavyweight structure of the building was used as a thermal store, which would build up heat during the summer and slowly give it back over the winter.

Hence Mike wanted to repeat what he knew worked well. Portree Passivhaus is a masonry building with a cavity wall.

This is unusual for Scotland which has a lot of timber frame buildings, that are quick to put up in the inclement weather.

Resilience was another key factor

The building's heavyweight structure will also make it a ‘fortress' for whatever weather is to come.

I think it’s inevitable that we’re going to get more extreme weather. We haven’t had that much of it in the UK yet, but there’s rarely a week when there isn’t some kind of extreme weather event somewhere in the world which makes it into the news.

The slab of insulation goes in

The building sits on a tray of insulation

Concrete is poured into a tray of insulation to form the lower ground floor slab. The internal concrete block walls then get built onto the edges of that slab, so the internal part of the house is completely isolated.

The cavity wall is 375mm wide and uses TeploTies for low thermal transmissivity.

With a large open plan living area, the building requires a steel structure for extra support.

The first floor is a beam and block floor, and above this there will be a green roof.

We’ve got a very substantial roof structure in order to take the weight of the soil on which the grass will grow on the roof. But below that, sitting on top of the structural I-beams, there’s another layer of insulation.

There is no environmentally benign dwelling

Mike is well informed when it comes to climate change and believes that we, as a world, could be doing so much more to reduce carbon emissions. So why is he building with masonry when more sustainable materials exist?

There’s undoubtedly embodied energy in this house. How significant it is in terms of global carbon emissions compared to things that could be very, very easily avoided, I don’t know. In use, the house will have a tiny environmental footprint. It’s very energy efficient, it doesn’t have a heating system, it’ll have renewable energy systems as well.

Although it will be a number of years into the future, Mike says the house will pay back its CO2 debt. And for him it's not just about preventing climate change, this is a house that's ready to face the extreme weather events that have been caused by climate change.

When you look to the future it's not going to blow down. And the turf roof is part of the resilience strategy.

Mike installing the ventilation ducting

Mike gradually took on more responsibility

Having been very hands-on during his first self build, he had wanted to do less this time. However, he's found himself being drawn in!

Due to concerns over finances, he decided to save some money by installing the mechanical ventilation system and doing all the electrics himself.

But knowing the level of detail required on a project like this, he's also monitoring quality.

It’s all about during and post construction quality control. And trying to get across the message that the insulation has got to be kept clean and dry – difficult in this climate – as dry as possible and put in neatly without any gaps – I don’t know why but it’s just proved to be very tough.

So Mike has spent weekends pulling insulation out, cleaning it, putting it back again. He's also taken responsibility for some of the trickier details.

Mike spotted a thermal bridge across the cavity

With an architect and contractor who haven't built a Passivhaus before, Mike's experience has become extremely useful. During construction he noticed that the steel was creating a thermal bridge across the cavity.

The solution was to shorten the steels and put thermal break pads in. Using stainless steel bolts also helped reduce the transmission across the steel.

Delays have had an upside

Mike's contractor has had to start another project for a local hotel and this has meant a reduced workforce on Mike's site.

However, as pensioners, Mike and Lizzie have been able to squirrel away extra cash.

This gives Mike cautious optimism that he could get towards the end of the project… and even hire decorators (something they'd really like to do).

Stone cladding begins
The main living space

Find out more

Visit the website of Portree Passivhaus

Follow Mike Coe on Twitter

Follow Portree Passivhaus on Twitter

Transcript

Download a transcript of the interview with Mike Coe.

Please connect with me

Subscribe, rate and review the podcast in iTunes

Rate and review the podcast on Stitcher

Like our Facebook page

Follow us on Twitter

HPH215 : 10 things I’ve learned during construction – with Ben Adam-Smith

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Ben Adam-Smith reflects on what he's learned so far during the construction phase of his self build.

The project is halfway through and the finished house will meet the Passivhaus standard.

1. Things move quickly

If you're a first time self-builder I'd wager it's taken you a number of years to get to the build!

You've probably spent time dreaming and then looking for land and then going through the design process.

For all this work you have nothing physical to show.

So when it actually gets to the build and you have a team turning up on site every day, the progress is marked.

Yes, you've got this all in a schedule but sometimes things don't register until you see them!

I visit site two or three times a week and I'm always amazed what they've achieved.

 

2. Your team is probably bigger than you think!

Hiring a local contractor may give you the impression that you are hiring a small team.

However, building a house requires a great many skills. That means your core team will use sub-contractors where they see fit.

Sometimes this might be for speed. For example, brick-layers were drafted in when the superstructure was going up (even though the core team could have done this).

Or it could be a specialist skill is required such as electrics, plumbing, laying a screed, etc.

3. The flow of supplies is half of the progress

You can’t do anything without the materials. They need to be on site in the right order and ready when needed.

Sometimes a lot of progress can be made in a single day.

For me, a great example was when the beam and block floor went down.

Organising the precast concrete beams and filling in the blocks happened in a short space of time.

Watching this process you see people with their different roles. One person will be operating the telehandler and just bringing new packs of blocks. Another person might be distributing these blocks, while another person is technically doing all the building (and laying them)!

4. The quality of the build is a team effort

Watching the construction phase unfold before you it is clear that everyone is contributing to the finished product. Perhaps more so on a masonry build like mine, because there are so many little elements that come together.

Whether it's mixing cement, laying blocks, putting in insulation, or the thousands of other little jobs, everyone must be putting in 100% to have a high quality finish.

 

5. As a client, you need to keep ahead with the decisions

When you take on a self build you are aware that a lot of decisions are coming your way.

The good news is that these don't come all at once. There are definitely moments when the decision-making intensifies. One of those is during specification. The second peak is during construction.

As we put a lot of detail into our tender documents we thought there wouldn't be that many decisions to make during construction. Wrong!

If you've left any PC sums then get to work as soon as possible. Your contractor is not going to want to be delayed and may apply pressure accordingly.

The whole way through we've been asking our contractor what is next, what is next? Thus we have stayed ahead of the curve so far.

 

6. As a client, there’s a huge benefit to regular site visits

I try to get to site every two to three days. Why? Well, firstly I love it. I've seen so many other houses come to life that I want to make the most of seeing progress on mine!

It's also a great way to build relationships. I always aim to know the name of everyone working on site and find out a bit about them. When you're knee-deep in emails and texts, I like to balance that up with real life contact.

The other reason it's useful is that you can often answer questions or pick up on little things.

Finally these site visits are good for understanding your house. I may have stared at plans for hours but everything becomes clearer when you can see it in practice.

 

7. Problems that arise can generally be solved

Throughout a self build issues will arise. At the time it can feel like the end of the world. Of course, with a positive mindset there's a way through. Normally a bit of discussion and a few decisions can get you back on track.

 

8. Best-made plans might need to change

I've tried to embrace the philosophy of not changing my mind too much during the construction phase.

This is sound advice because there can be ramifications to changes (which will translate to delays, additional cost and crushing morale).

However, some aspects are not set in stone and can evolve without much or any extra work.

I guess it's about catching those things in time.

One example of this on my project was the nagging thought that we'd put too many bathrooms in upstairs! Initially I vowed to live with it. The thing is that it hadn't happened yet. And the more we thought about it, the more we realised this space could still be useful, just with a different purpose. So, for now it's for storage. Who's to say it doesn't transform as we need it.

9. Masonry construction feels old-fashioned!

My build is a masonry cavity wall construction, which is both traditional and popular in the UK.

It's often chosen because there's a solid skill base available and it's cost effective.

However, sometimes it does seem quite manual.

There's a lot of cement to mix and blocks to arrange. String lines are used . . . the tolerances are not as good as other build methods. Not forgetting there's a lot of embodied energy wrapped up in this approach

All that said, it is still the main way we build things in the UK. Who knows how you change an industry?

 

10. Being a client is a full time job!

We have hired an architecture firm and have a main contractor. It doesn't get much easier than this.

Even so, it's still been exhausting at times!

So don't overstretch yourself. If you're planning to project manage, for example, make sure this is within your skillset and you realise what you're taking on.

I cannot fathom what it would have been like with extra responsibility on my build!

Please connect with me

HPH205 : Specifying a house and creating tender documents – with Dan Higginbotham

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Architectural technologist Dan Higginbotham from Parsons + Whittley Architects talks about producing construction drawings and a scheme of works from an architect’s design.

Interview with Dan Higginbotham

Dan has worked with Parsons + Whittley for over 15 years, as an architectural technician and now also as a director. He has recently been working on Ben and Kay’s project and previous work includes housing developments built to Passivhaus standard.

The architectural technologist details how the building is constructed

Dan’s usual role is taking the architect’s 3D conceptual model and making a full set of construction drawings that someone can actually build from. These include plans, elevations and sections. As he says, “What we try to give them is a comprehensive package of information that they’re able to sit down and accurately price.”

For a Passivhaus like Ben’s, more detail is required to ensure airtightness and avoid thermal bridges. Dan explains that there’s less risk with a house only satisfying building regs, as it would probably still pass if not sealed to such a high standard.

Being methodical helps identify all the details

Dan admits that things can get missed during this complex process. He tries to avoid this by following the same method each time but this is hard as he mostly works on one-off projects.

Additional complexity comes from the many different methods of construction, and the level of sustainability clients are trying to achieve. As Dan summarises, “Although you can re-use ideas that you’ve done before, you generally have to start the whole process again depending on how people want to construct it.”

Keeping industry knowledge current is important

New products and resources may result in faster or more sustainable construction and better dwellings overall. Dan explains, “You’re forever learning new things, new technologies, new ways to construct things, and we just somehow have to try and keep up with that process and the industry, really.”

Up-to-date knowledge might come from “build indexes”, forums, word of mouth, or working for a particular client. For example, a housing association might require modern construction methods or certain levels of sustainability. Dan has also found big social housing sites useful for finding out about cost-effective materials or shortages.

Cost, simplicity, speed and specifications all affect construction decisions

A shortage of materials could affect how you design or build things. Ben and Kay’s house will use a traditional cavity build method but this decision was threatened by a shortage of concrete blocks just before work started. Likewise, a current shortage of PIR means seeking alternative insulation materials.

Deciding on construction materials and methods is a whole team process, with input from Dan, architect John, and practice partner Chris. It helped that Ben and Kay had already selected the finishes of the building envelope. The render finish and brick plinth suggested a cavity wall as cost-effective and simple to build, albeit with more insulation than is traditional.

Items specified may change at a later point

Looking at drawings for Ben’s build shows the level of detail required. The elevation showing the joinery specifies some items that they will not necessarily end up with. For example, after various discussions, an alternative supplier may provide the windows. Dan says this is quite normal: he prefers to obtain an accurate cost from a supplier rather than leave the cost as a provisional sum.

The floor plan shows 150 mm of insulation in the cavity wall, enough for this relatively large property to get through the Passive House Planning Package. Although Dan specified high performing Knauf Earth Wool (with a thermal conductivity of 0.032 W/mK), the contractor may choose an equivalent mineral wool.

Ecological aspirations need to be balanced with budget

The section of the different floors shows lots of junctions that need to be considered, especially because it’s a Passivhaus. Dan tended towards methods and materials familiar to most builders rather than potentially expensive ecological features.

Another requirement was that height be kept to that specified on the planning drawings, so Dan avoided any ecological products where more material was needed for the same performance values. He explains the choices as detailed on the section:

  • A strip foundation supports a cavity wall construction.
  • The first floor is beam and block containing PIR insulation to give a thin but solid construction with the performance needed. Above is a screed with membranes and airtightness products in between.
  • The floor and walls specify a very lightweight Aircrete block to get the best performance while minimising thermal bridging at the junction of the wall and floor.
  • The internal walls are traditional studwork or blockwork where necessary for support.
  • The second floor uses a pre-manufactured metal web floor joist (or Posi-joist) that gives a structurally sound floor with space to route the MVHR and other services without having to laboriously cut holes.
  • At the top is a fairly standard, traditional truss roof, with a more complex catslide roof to the rear. To avoid complex steelwork and associated thermal bridges and/or airtightness problems, the roofing truss suppliers came up with a truss that could form the catslide as well.

Sections help contractors avoid thermal bridges and ensure airtightness

Drawing more sections is useful where there are difficult details in the building, including all the junctions. Where each part of the building is different, more drawings may be required. Ben’s Passivhaus is fairly linear, but Dan was careful to show all the construction details so nothing would be missed.

The four sections include one of the garage, one “typical” house section, one of the stairwell arrangement, and one showing the ground-to-first-floor French door, window and boarded panel arrangement.

Developing the electrical plan is iterative

Dan uses his experience to determine locations for electrical points, taking into account where the furniture will go. However, these positions might change later. As he says, “Each client will have their own input, particularly on light fittings and lighting locations.”

A flexible space, for example the spare bedroom doubling as a study, can take more time to work out, as he explains to Ben, “Once we’ve actually physically got the space on site, yourself and Kay might then go, ‘No, actually I want a few more sockets here.’” This is typical of the process: educated guesses on paper are reappraised once the rooms are built.

The team liaise with a consultant for the mechanical design

Alan Clarke is the consultant for the mechanical systems on Ben and Kay’s project: the MVHR design, the hot and cold water supply and heating the property. Dan and the design team work with Alan on decisions like budgeting for the right boiler and the site for the MVHR.

A major consideration is distributing the ductwork within the property. Most of the pipework is routed through the open webs of the intermediate floorspace with additional risers to the first floor. On the second floor landing a false ceiling provides a service void where ducts are routed to each room.

The schedule of works provides more information for the contractor

After completing the drawing package, Dan itemises every detail in the schedule of works. Reading this document alongside the construction drawings enables the contractor to produce a priced specification and to understand the methods and materials of the project.

Find out more

View Dan’s profile on LinkedIn

Visit the website of Parsons + Whittley

Transcript

Download a transcript of the interview with Dan Higginbotham

Please connect with me

HPH134 : A new build cavity wall Passivhaus – with Angie and Paul Dallas

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Angie and Paul Dallas explain why they opted for a Passivhaus, and the benefits of getting involved with the build.

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Interview with Angie and Paul Dallas

Angie and Paul had been looking to build a comfortable, energy efficient house that they could retire in. There was no issue with finding land as their existing house had enough land available, albeit with its own planning challenges.

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It took 5 years to be granted planning permission

Angie says that the planners weren't necessarily against their plans, but the Highways department had to consider the problem of access because of the limited number of houses that could be on their unadopted road. The house is in a conservation area so that presented its own challenges, and there were a number of trees in their garden which had preservation orders on them.

After initially having their application rejected, they won on appeal in London.

A planning consultant helped with the process but in hindsight they think they should have appointed him earlier and benefited from his expertise in areas where their architect was struggling.

The decision to build to Passivhaus standard was taken after planning permission had been granted

It was on a trip to look for triple glazed windows that Paul started chatting with one of the directors of the Green Building Store who explained the differences that Passivhaus had from normal building practices. Coming away from that meeting Paul was convinced that, even if they didn't strive for the full Passivhaus standard, he wanted the building to at least use the principles of high design quality.

Deciding to pursue this approach meant some design changes to their original plans. The amount of glazing had to be adjusted together with the orientation, but the actual size and construction wasn't altered.

Being involved in the construction had its benefits

It had always been important to Paul to be actively involved in the construction of his house, however once the decision had been made for Green Building Store to take on the project to Passivhaus standard he was unsure what his role would be because his knowledge of the area was limited.

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Whether Paul would be able to assist with the labouring was a decision for the building team, and Paul was careful to take his time and show that he could muck in and not be a pushy owner. Eventually he was invited to join the team and he relished learning on the job and taking their instruction.

One of the greatest challenges that Paul found was working on the site throughout the British winter. If the roof could have gone on during the summer months it would have been a much easier build.

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A key benefit of Paul being on site was that if a problem arose or a decision needed making, he understood what was going on and could make the choice straightaway.

Paul found the camaraderie of being on site extremely enjoyable and believes the pride in the house afterwards far outweighs the efforts of doing it.

“And to be honest I don’t think I’ve ever laughed as much during a job ever. I thought it was great fun.”

The comfort of the house has lived up to their expectations

The temperature of the house remains fairly constant and the mechanical ventilation heat recovery system means that the air quality is good everywhere. Angie also notes that it seems to stay cleaner and that since having pollen filters put in she has also seen health benefits compared with their old house.

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Take time to appoint your design team

Their first architect, although designing a great scheme, didn't have the time to take it from there. Paul and Angie wish they had taken time to research, interview and appoint a replacement architect but instead they appointed someone on recommendation, who professed to be an architect but actually wasn't. He claimed that the original plans couldn't be built, but it took Angie and Paul several months (and £6,000) to have the courage to dismiss him and get somebody else. Thankfully the next architect they appointed confirmed that they would be able to build to their original plans. Paul emphasises the importance of researching specialists and finding someone that you feel comfortable with.

“If you’re building a Passivhaus you want somebody with experience of Passivhaus or at least is willing to learn and look at the differences between that and a normal house and take those on board.”

Deciding to use the services of an interior designer they were fortunate to have them involved at an early stage to assist with the layout of the interior and pick up on areas, such as space for hanging curtains, which would have been difficult to rectify after the construction work had been completed.

Green Building Store provided them with knowledgeable and skilled builders who Angie and Paul both say were a pleasure to work with. They used their own electrician and were also happy with the services of the plumber.

Paul stresses that it's important to take your time at the stage of getting your team together. They were thankful that their whole team worked well together and that they enjoyed working with them.

“And it’s people you can work with as well. It’s not just a good track record but if you’re not comfortable with those people then it’s going to be a problem down the line.”

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Find out more

Visit the website of Green Building Store

Check out the shortlist for the 2016 UK Passivhaus Awards

Please connect with me

HPH105 : How Far Should You Go with a Low Energy Retrofit? – with Bob Prewett from Prewett Bizley Architects

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Bob Prewett, a director of Prewett Bizley Architects, shares his approach to low energy retrofits and explains why he sets energy targets on a project by project basis.

Bob Prewett

 

Interview with Bob Prewett

Prewett Bizley Architects specialises in low energy architecture and Bob has a particular interest in retrofit. He explains that housing is responsible for around 27% of the UK's carbon emissions, so buildings of all ages and styles have a part to play in terms of energy efficiency.

 

There is a Distinction Between Retrofit and Renovation

Bob's partner, Marion Baeli, defines renovation as being smartening things up to make them look good and dealing with the top 3mm of construction. Retrofit on the other hand is about getting under the skin of things and sorting them out at a fundamental, architectural and building physics level.

Residential-Retrofit-Front-Cover

What to Consider when Commencing a Retrofit Project:

  • Get advice at an early stage
  • Create a whole house plan which identifies where the energy savings might be, along with the risks associated with tackling them, and how these might be actioned
  • Form a clear strategy of how these will be dealt with, either all at once or as stages over an extended period
  • Be aware that there is no ‘one size fits all' when it comes to retrofit.

“It's not for the faint hearted, either in spirit or in finance”

 

“Understanding What the Quality of the Building is and Then Designing and Planning Very Carefully to Not Upset That Balance”

Bob is concerned by evidence of the careless nature of works being carried out to some buildings which, with moisture being allowed in and then trapped, can actually be causing damage. He looks at the example set by Germany on the other hand which takes a more considered approach, doing gradual, quality improvements over time, instead of trying to do multiple houses quickly and cheaply.

“Germany still have a confidence about the future and progress and a belief that just doing things well now is an investment for tomorrow. “

 

“We're Interested in Taking the Building to Where it's Going to Sit Happily”

Rather than starting off with a target value in mind, Bob believes that it is important to understand the building as a whole and take it to where it's going to sit comfortably, and not push it too hard. Some buildings will get to a U-value of better than 0.15 or 15kWh per square metre relatively easily, but for others, such as historic solid wall construction, they are probably not going to want to go there. Bob explains that they are interested in taking the building to where it sits happily, even if those values are a little higher. He would expect most buildings that don't have insulation or good quality windows to easily achieve a 60% energy reduction, and perhaps even going up to 90% in some cases.

Significant energy savings will be achieved by using a holistic approach to deal with insulation, airtightness, cold bridges, windows, walls, roofs and floors. It is important to understand the building and how these elements interact and work together.

“Some buildings will be predisposed to very high energy savings, some will be predisposed to doing a bit less.”

 

Be Strategic About What You Purchase if You're Actively Looking to Retrofit

Bob has purchased a 1960s small terrace house which should leave them with enough money left over to do a good retrofit. He deliberately decided against listed properties and those with planning restrictions as he felt it would be a higher risk approach with energy savings being more difficult to achieve.

They intend to take advantage while the roof on this property is being done to pass brushes between the cavity walls and give them a good clear out before adding cavity wall insulation.

Changes being made to the roof at Bob's own house

Changes being made to the roof at Bob's own house

 

Internal wall insulation and airtightness measures

Internal wall insulation and airtightness measures

 

New light slot

New light slot

 

Airtightness results of 0.6

Airtightness results of 0.6

 

Carefully Consider Your Insulation Options

External Insulation – This can seem like the most simple option. There is potentially very little disruption and you are likely to be able to continue living there while the work is being carried out. You're cloaking the building, keeping it warm and dry and therefore less likely to suffer moisture problems. The biggest drawback is that it completely transforms the building architecturally, which may not be to yours or the planners liking. In terraced houses you can end up with cold bridges left over through party walls.

Internal Wall Insulation – This has the benefit that it does not have an impact externally so there aren't the same planning issues as above. There will be far greater disruption inside however and possibly not be in a livable state. The process can be quite slow and be impacted by various pipes, electrics and other services. There are also cold bridge issues when getting to things like window junctions.

Cavity Wall Insulation – If you have cavity walls then filling them can be a good option. Bob however advises caution and not always accepting the claims of the installer that it is suitable for the wall, without following up with further questioning. There may be some situations, such as bad pointing or a coastal property with porous bricks, where it might not be an appropriate choice.

 

The 80% House was a Defining Project

This was one of Prewett Bizley Architects' first deep retrofit projects. The client wanted excellence and was prepared to pay to achieve it. During the closing stages of the project, in an extremely hostile winter and before the heating system had been commissioned, Bob would visit the house which maintained a temperature of around 18 degrees. Even though the systems weren't all running, he was struck by the quality of the environment. Even leaving aside the benefits of energy efficiency, it was the feeling of the house that made a huge and defining impact on him and was the reason why they continue doing these kinds of projects.

80% House

80% House

Hackney 80 per cent house drawing

Hackney 80 per cent house living room

Specific Heat Demand

Specific Heat Demand

Year 1 Gas Results

Year 1 Gas Results

“If you do it really well you just get this amazing quality of environment as a backdrop to our life.”

 

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Transcript

Download a transcript of the interview with Bob Prewett.

 

International Passive House Days

As Bob Prewett explains, it's really about the feel of the house and the quality of the environment, which is why the International Passive House Days are the ideal opportunity to experience it for yourself. Each year Passive House residents fling open their doors and invite people in to have a look around and ask questions. This year they will be taking place around the world on 13-15 November 2015. Keep an eye on the International Passive House Association website to find out which buildings near you will be open to view.

International Passive House Days

 

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