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  • HPH376: What is WUFI? – with Toby Cambray

    HPH376: What is WUFI? – with Toby Cambray

    Toby Cambray talks about the risks associated with moisture in buildings, and the modelling techniques – like WUFI® – that can be used to assess those risks.

    Interview with Toby Cambray

    Toby Cambray co-founded Greengauge building & engineering consultancy in 2010, specialising in sustainable and low energy design. He is a certified Passivhaus Consultant  and has completed a PhD on moisture in buildings.

    Condensation on windows is a common sight in British homes

    In buildings, moisture is water in any form

    When we use the term ‘moisture’ it can refer to liquid water, water vapour in the air, or even ice. People might be most familiar with water vapour, and how humidity changes with temperature.

    It’s also important to think about materials – especially historic building materials – and how they interact with liquid water. And when you add insulation to buildings, moisture is something that really needs attention paid to it.

    Moisture movement in buildings is about equilibrium

    In the laws of physics, all things try to minimise their energy. For example, if you have an area of high pressure next to an area of low pressure, the molecules try to ‘even themselves out’ and minimise the total net energy. In a different context, that’s what is happening with moisture. In an area of high vapour pressure with lots of water, the water will try to distribute itself as evenly as possible.

    The potential risks from moisture in buildings are varied

    Organisms that cause mould or timber decay can thrive where moisture is present. Moisture also leads to problems like corrosion, especially of steel. In heritage buildings, it can lead or contribute to deterioration in masonry, through processes like freeze/thaw damage, or salt transport and crystallisation.

    Damp and mould inside a historic building

    The two main moisture strategies are moisture open or moisture closed

    Putting it very simply, you can either manage moisture or block moisture. Most modern buildings are moisture closed, or moisture blocking. Features like damp proof courses and vapour control layers aim to stop moisture getting to where we don’t want it.

    In traditional buildings, when these modern products obviously weren’t available, builders worked with materials in a way that managed moisture – often by absorbing it and holding it, before allowing it to dissipate safely. Porous materials like stone and brick can generally store and transport both liquid water and moisture vapour.

    There is still a lot to be understood about moisture in buildings

    Toby has been carrying out moisture modelling work for over a decade. Any simulation has shortcomings, so he sees it as the responsibility of practitioners to understand as much as possible about the physics of moisture so they can then understand when models are most useful. Toby acknowledges that he still has lots to learn about the physical processes that calculation models are trying to simulate.

    Dew points are not the best way to assess condensation within building structures

    While we want to avoid condensation within the structures of our buildings, dew points are not always a great way to understand potential moisture risks. This is especially true in masonry materials and traditional constructions. A dew point is the temperature at which condensation occurs for air of a given humidity.

    Simpler calculation methods that rely on dew points, like the Glaser method, don’t reflect the full range of real-world conditions. They don’t take account of rain on the outside of the building, or moisture transport and storage in liquid form. Their limited scope might be okay for some situations, but they are not sufficient for making sensible judgements about many structures, including historic buildings.

    For example, you could have a structure that never suffers from condensation, but still gets a serious problem like mould. The calculation method might tell you about the condensation risk, but it isn’t sophisticated enough to calculate that humidity is high enough for mould to form.

    WUFI software is a more complete way to simulate moisture movement

    It’s not perfect, but it is a more complete approach to modelling moisture movement in buildings and modelling how water moves around within porous materials.

    In the software, the user builds up the element to be modelled. They then select a climate file with data about sun, wind, temperature, humidity and rain. Then the internal conditions are inputted, some other parameters are set, and the simulation can be run. And the simulation predicts the temperature and moisture content at any point within the element’s structure. Using the temperature and humidity profiles that it outputs, together with some post-processing tools, it’s possible to assess whether problems like mould could occur.

    Temperature and relative humidity data over time

    There are still uncertainties in WUFI calculations

    As with any software or calculation, nonsense in leads to nonsense out. The WUFI software has a database of several hundred materials. Some are modern products with known performance.

    It also includes porous materials. Because these materials have unique combinations of liquid transport properties and vapour permeability, there can be enormous variation even within a single category of materials. For an existing building, some assessment and measurement of the material is needed to then make an informed selection from the database.

    Other uncertainties include internal conditions. For example, you might not know if you should be accounting for a densely occupied house with poor ventilation. Toby explains that the advantage of modelling is that you can play around with some of these variations and explore the different issues to understand their effect.

    An example of how moisture moves within a wall build-up that has wood fibre insulation

    The simulation is quick to run, but interpreting the output is key

    Toby says his team likes to spend a couple of days on a project, normally. This gives time to go to site, collect material specimens and analyse them. Once the data is available to enter into the software, the actual simulation can take anything from five minutes to a few hours to run, depending on complexity.

    The real value is in the interpretation of the results, and providing a professional opinion and risk assessment. In complex situations, things are much more nuanced than a simple pass or fail. It can often mean going back to a design and altering it to reduce risk further. Toby’s work really comes into its own in more unusual situations with higher risk constructions, perhaps featuring an unusual combination of materials.

    There are lots of good sources for help and advice

    For simpler enquiries, Toby and the team at Greengauge will often direct people to a variety of reputable suppliers who they have built relationships with over time. Examples include Ecological Building Systems, Back to Earth, Natural Building Technologies (now part of SOPREMA), and Best of Lime.

    For WUFI calculations, there are no specific qualifications to look for when engaging someone. There are a small number of training courses, but a lot of it comes down to experience: reading academic papers for background, and looking at buildings on site to understand the difference between simulation and reality.

    The most common use of WUFI is with internal insulation

    A sophisticated modelling tool like WUFI is most suited to applications that have a lot of variables. That’s particularly the case in retrofit, where we have no control over the existing construction and we need to be careful about what we do to the structure to avoid introducing moisture problems.

    In new build construction, we tend to have a good idea of what works, especially if following prescriptive solutions. In that case, there’s no need for complex calculations. BS 5250, the code of practice for moisture in buildings, has guidance about when different calculation methods ought to be used.

    An analysis of water content over time

    A consistent layer of thin internal insulation can help to manage moisture

    Using hygroscopic, capillary active and vapour open materials helps to maintain a wall’s ability to dry to the inside. Generally, the thicker the layer of insulation applied to the inside, the harder it is for that drying to happen. Most people are now using 40mm, 60mm, or possibly 80mm of wood fibre insulation, and that seems to work okay in most places. A continuous layer of 40mm of insulation, with thermal bridges resolved, is much more effective than a thicker layer of insulation that’s hit and miss.

    Our podcast with Martin Twamley discusses this subject in more detail.

    An internal wall insulation strategy from Steico

    Using WUFI can stress test a construction

    Good practice when doing a simulation is to include moisture loads or moisture stresses. This is something WUFI allows the user to do which simpler calculation methods can’t. It’s possible to allow for a certain amount of rain coming in through a crack, or a certain amount of warm air moving out through the airtightness layer.

    Find out more

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  • HPH328 : Insulating internally with a thin layer of wood fibre board – with Martin Twamley from Steico

    HPH328 : Insulating internally with a thin layer of wood fibre board – with Martin Twamley from Steico

    Martin Twamley from Steico explains how to use breathable internal insulation, while avoiding the risks of condensation and mould.

    Interview with Martin Twamley

    Martin Twamley is Technical Director of Steico UK. Steico have been producing timber-based materials, predominantly structural timber and insulation materials, since the 1960s and selling them across Europe. Using only pine and spruce they make a number of different products, and will always provide guidance as to what the correct product would be for the required application.

    “Once people start using timber and understanding it, it’s a sort of material that you fall in love with, and you then change your building process.”

    The products have low embodied energy

    Structural products like I-joists were first used in the USA and the motivation was that it was the most sensible use of the raw material. However, as a natural material and one that goes through little processing it also has a low embodied energy, and will even lock up carbon.

    Laminating the veneers strengthens the product

    The I-joists are created from Laminated Veneer Lumber. They are made by peeling a tree, creating 3mm veneers, and then bonding them back together. This means that individual weaknesses are removed and spread across the whole product. The strength-to-weight ratio on engineered timber is then much greater than it is for solid section timber as you’re getting a much stronger product for less raw material.

    There is very little manufacturing waste

    Martin explains that the good thing about producing both structural and insulation products is that there is very little waste. For the structural timber they use the de-barking and peeling process. For the insulation materials they use chipping and milling. Therefore, what they can’t use for the structural timber they can use for the insulation. What they can’t use for the insulation they can use for producing their own pallets. And if they can’t use it for pallets they have a biomass power station where they can use it for electricity generation.

    UK housing stock has a need for internal insulation

    The UK housing stock is some of the oldest in Europe and is in desperate need of retrofitting. With a reluctance to insulate externally and change the appearance of this historic solid wall housing, internal insulation may be a better solution.

    The traditional way of doing this is with systems that try to block the moisture, rather than being able to control it. When you try to block moisture there can be an issue with getting it trapped inside the building instead. This potentially adds risk to the fabric of the building, because of mould and condensation problems.

    The Steico wood fibre internal insulation system allows water vapour in, controls it, holds it, and then lets it out again.

    Standard insulation installations are vapour closed

    These typically are the foil-backed polyurethane type materials that are either on a frame system or dot and dabbed onto brickwork. In theory they don’t let any moisture in, which is a good thing for the fabric. This can however lead to high moisture levels internally, so you might need to consider an MVHR for example. Mould will happen when warm air gets behind the plaster board and hits the cold wall surface. It might not even be until years later that the mould shows itself on the internal surface.

    “When people think about air quality, they generally think about external air, but we spend 90% of our time indoors. It’s the internal air that we’re breathing. So that’s what’s impacting our health.”

    These are the kinds of systems that tradespeople and DIYers are most likely to use, because they’re readily available. Also, homeowners are primarily just thinking about thermal performance in the winter. But actually, when you consider a holistic approach that takes into account all the possible issues, the material choice is incredibly important.

    Internal insulation doesn’t have to significantly impact on the room size

    Martin talks about applying a thin layer, typically an optimum amount of 40-60mm. Even in relatively small rooms that’s an amount that won’t really be noticed.

    What works for one building, won’t work for every building

    What works for one elevation of a building might not even work for a different elevation of the same building, because of different weathering exposure. This is why it is so important to have an assessment done, particularly if you’re looking for a really low U-value. Martin explains that generally speaking a 40mm or 60mm board on standard brick will work in the majority of situations.

    Take the wall system back to bare brickwork if possible

    The wall system should be as breathable as possible. That means that you don’t want anything on the internal side that hinders water vapour movement, such as impermeable layers, cement-based plasters and renders, and paint layers.

    The external face is also important to consider (such as renders and re-pointing), because this is where the majority of the water is coming from.

    With this natural, breathable approach, there is a full bonding layer (typically a lime based product) between the insulation and the wall. This is in contrast to a traditional approach that would have a cavity. The fact that there is no cavity means that there is no collection of liquid water, which is what leads to mould and condensation issues. Instead, any moisture is either passed onto the brickwork and out the front, or it can go back to the inside.

    Pay particular attention to the critical areas

    Window reveals are particularly important. If you have a warm wall surface, then the window reveal will be the coldest area. If you don’t insulate into that reveal then that is where all your condensation will form. Martin suggests that with a 40mm or 60mm on the wall, a 20mm board on the reveal will be fine.

    Another critical area that could be overlooked if somebody is insulating ground and first floor, is the void where the floor joists connect into the wall. These can be cold spots where condensation will be much more of an issue than it was before. To prevent this, you can tape around the junction of the joists to the existing wall. This stops the route for convected airflow into the wall.

    Where you have internal walls connecting with external walls can also be problem areas. If you’re insulating the external wall, then the corner of that internal junction can be quite cold. Steico make a wedge-type product of thinner insulation that can go into the corner to stop the condensation risk.

    There are useful resources available

    Martin makes reference to The Guide for Sustainable Renovation, by The Pebble Trust, as being a valuable resource for anyone taking on a retrofit project. It gives advice with a holistic approach that considers all of the moisture risks involved.

    The carbon storage element of materials is often overlooked

    A frustration for Martin is that in the UK he thinks we tend to be quite product agnostic. It is very much that if you achieve a certain performance level then it doesn’t matter what you use to to get there. He compares this with Bavaria, Germany, that has a new system brought in by local government. They are offering a 500 Euro grant for every cubic metre of biogenic carbon locked up within the fabric of the building. In the UK we have U-value targets, but nothing that looks at the amount of carbon stored within the fabric, or the type of material that is used.

    Find out more

    Visit the website of Steico

    Follow Steico UK on Twitter

    See Steico wood fibre insulation being used on Buckinghamshire Passivhaus (a PH15 project). Join The Hub to access our in-depth video case study.

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  • HPH195 : What is cellulose insulation? – with Gordon Lewis

    HPH195 : What is cellulose insulation? – with Gordon Lewis

    Gordon Lewis explains what cellulose insulation is, how it’s applied and why self-builders can benefit from choosing it.

    Interview with Gordon Lewis

    Gordon Lewis has been involved with cellulose insulation for over 26 years. He mainly works installing Warmcel insulation into timber-framed properties.

    Choosing insulation material is important

    Cellulose became known as an insulation product in the early 1980s. Made from recycled newspaper, it is a highly sustainable product. The newspaper is milled down to make the fibres much smaller, then fire-retardants are added.

    Gordon admits that man-made insulation materials are likely to continue in the market but he is optimistic about the alternatives, saying, “Cellulose is slowly creeping back into the marketplace and doing a great job.”

    Paper use has declined but cellulose insulation is still available

    The growth in information technology has meant a decline in the availability of newspaper for recycling. Along with overhead costs, this has resulted in some factories closing. For example, Gordon’s former employer, Excel, the sole UK manufacturer of cellulose insulation, closed down in 2014.

    Sources of newspaper and cellulose insulation do still exist, however. There is one company in Ireland and there are many more manufacturers of cellulose on the continent. Gordon uses a brand called Warmcel, which is made by CIUR in the Czech Republic and shipped to the UK.

    Any timber-framed building can incorporate cellulose insulation

    Cellulose can be used for other build methods, but is ideally suited to timber frame buildings. Because it’s made from paper, it must be fitted in a way that avoids contact with any damp surfaces. There are a number of different materials that can make the “sandwich” containing the insulation; it might be rigid board on both sides, or one side could be a membrane.

    Different boards also have different thermal performances, so it is worth thoroughly researching all the materials involved. This includes speaking to people that have had properties built, architects, builders, or the installers. Gordon says, “Ask as many questions as you possibly can to get on the right foot, to say, ‘that’s the product that I need.’”

    Cost and quantity of insulation are based on location, depth and density

    In order to calculate cost and how much product is needed, Gordon considers where the cellulose insulation’s going, the depth of the space to be filled and the density required. Locations could include internal or external walls, floors, an attic space or a sloping ceiling. Gordon uses formulae to establish how much material is required for that particular build.

    Any moisture issues must be addressed prior to installation

    Generally, before any installation is carried out with cellulose, the building needs to be wind and watertight. Cellulose will dry up and cope with a certain amount of moisture, but not too much. For example a constant leak or rainwater continually getting in to the frame would cause problems. If the doors and windows are not in, those access areas can be masked off with polythene on both sides to stop rain being driven in. Gordon will look out for water or staining on boards from rainwater that may have dried up over a day or two. To inspect for damp before installing cellulose he might drill the wall and test by hand.

    Holes in the wall allow the insulation to be pumped in

    The cellulose needs to fill voids created by the timber frames and rigid boards, and there can be hundreds of them to find. Experience gives Gordon familiarity with typical frame kits so he knows the small gaps to watch out for, and how to access them. He can also identify them from the screw patterns, looking at the drawings, speaking to whoever fitted the boards, or even asking them to mark the boards showing whether or not there’s a gap. If there’s still any doubt, he may drill a small hole to check.

    Special sealing tape is used to maintain airtightness afterwards

    Once a hole has been cut to access each void, and the insulation pumped in, the core is sealed back over the board. To make it 100% airtight, the tape must have no creases. On the job where Gordon and Ben met, the PH15 build had close to 500 holes cut and repaired. The airtightness test showed below 0.01 air changes an hour at 50 Pascal; one of the best results recorded.

    After installation, moisture problems are rare and can be rectified

    In Gordon’s experience, once the insulation’s in, it’s there for the lifetime of the building. He comments, “As long as the fabric and the structure of the building is sound, it’ll be there forever and a day.” He has had few subsequent issues, maybe three or four over 26 years. He believes those failures arose because people didn’t understand the building needed to be wind and watertight.

    If mismanagement does result in a bad leak going into the insulation, it can be replaced once the building is watertight. Gordon explains, “We have to cut a large hole in the board, if it’s not too badly damaged, or the whole board is taken off, and then all that wet insulation is totally removed before it can be replaced.”

    Experience counts but self-builders can get involved

    While Gordon has a lot of expertise in his field he encourages keen self-builders to get involved, saying, “They can get to the point where they can actually install the insulation themselves, if they want.”

    When he’s been on jobs where self-builders have helped, Gordon has supervised everything and made sure the equipment is set up right. Gordon uses a Krendl machine that breaks up the fibre, and then blows it from an airlock through the hose to the delivery point. Knowing that each cavity is full enough is mostly down to experience, but there are tests to check the density and location.

    Cellulose insulation is gaining popularity

    Gordon sees a growth in using cellulose insulation in line with a wider increase in green building techniques. More people are demanding greener products and want the benefits of Warmcel or another cellulose product.

    He sees the market increasing slowly, saying, “People are looking to recycle as much as they possibly can. Whether it be the insulation, the boards, all sorts of things, and sourcing the material as locally as possible.”

     

    Find out more

    Visit the website of CIUR

    Transcript

    Download a transcript of the interview with Gordon Lewis

    Why the location of a self build is an eco consideration

    Ben Adam-Smith reflects on one aspect of his last house that he absolutely loved: its location. It was close to local amenities, and meant that Ben did a lot more walking and only needed one car for the whole family!

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  • HPH178 : Natural clay plaster wall finishes – with Clare Whitney from Clayworks

    HPH178 : Natural clay plaster wall finishes – with Clare Whitney from Clayworks

    Clare Whitney from Clayworks explains how clay plasters are made, their applications and why we might choose them over other wall finishes.

    Interview with Clare Whitney

    Clare Whitney has been working at Clayworks since 2009. The founders of Clayworks were specialists in cob building, even writing a book about it, and used clay onsite as a sustainable building product.

    Clayworks now manufactures natural clay plaster, having spent two years creating a consistent and tested product that can be ready mixed and made available to anyone in the world at any time.

    Clay is an ancient building material

    Clay is one of the most naturally abundant minerals. Clare says that clay blocks and clay building methods are being rediscovered all around the world as a sustainable material with relatively low carbon intake. Clayworks focus on the application of clay as a plaster.

    Clay plasters finish the interior walls of buildings

    Clay plasters are a mixture of clay subsoil, aggregates and some natural form of fibre, with clay acting as the binder. Clay absorbs moisture, so water intake is critical; too much or not enough affects the consistency. Clare explains that Clayworks comprehensively researched different clay minerals to get the mixture absolutely right, so that the clay will not crack or “dust”.

    Clay plaster differs from other wall finishes in several ways

    Clare says it’s hard to describe the aesthetic, as you really have to see and feel and sense them, adding, “It’s a completely different feeling to walk into a room with clay plasters.”

    Advantages of clay plaster include:

    A different aesthetic:• The patina is earthy and very soft
    • A slight texture gives depth
    • Clay doesn’t set, so you can create patterns and textures
    More sustainable than most other wall plasters:• Clay is a naturally abundant raw material
    • It doesn’t have to be quarried
    • The processing of clay plasters is minimal
    • Apart from transport, there’s relatively little embodied carbon
    Numerous health benefits:• Clay plaster helps regulate the moisture inside a building
    • Helps mitigate allergies and asthmas
    • Helps offset the effects of formaldehydes and indoor pollutants
    The robustness of the material:• The product is scientifically tested
    • Proven finish and durability
    • Transportable and widely available

    Clay plasters work with any type of construction

    Clay plasters are now used all over the world in cities and in steel and modern buildings. However they have typically been used a lot in straw bale constructions and buildings with a lot of timber, due to their moisture-absorbing properties, and also in Passivhaus and other buildings where sustainable building products are key.

    Furthermore, clay plaster helps to absorb odours and has very clear acoustic advantages, making it ideal for use in bathrooms and kitchens.

    Materials can be beautiful as well as functional

    Although their clay plasters were originally marketed on sustainability and health credentials, Clare says designers and architects have adopted them for their aesthetic qualities.

    Clayworks’ plasters are now being supplied to customers all over the world; Clare attributes this success to their ease of use and the fact they can be trusted to stay on the walls and hold patterns, sculptures and shapes. Commercially their clay plasters have been used to fit out of well-known chain restaurants and public buildings.

    You don’t need to paint clay plasters

    Clare makes the point that although their clay plasters are a little more expensive than other wall finishes (starting at around £20 per m2), the overall cost is probably similar because:

    • You never need to paint them
    • They are through-pigmented, so you won’t notice a discolouration if they become chipped
    • They’re easily repaired

    Part of Clayworks’ research included coming up with a very comprehensive range of colours using natural mineral pigments. Clare explains, “We make colours in a fairly infinite mix. We’re always making up colours to people’s specifications…we can do a lot of turquoises, blues, greens and we’ve even done pinks and purples over the years.”

    Different types of plaster have particular uses

    Clay plasters are ideal for internal walls and ceilings throughout a house. The only areas to avoid would be wet rooms and exteriors, where Clare would recommend lime plasters, as they are more water repellent.

    Clay plasters can also be used for feature walls and fronts of other surfaces such as kitchen interior bars and similar furniture-type applications.

    If you can plaster, you can use clay plaster

    Clare says you don’t need specialist skills as clay plasters are applied like any other plaster; it just takes a little longer because the clay is a slightly different consistency.

    There is a series of different layers and depending on the substrate, you would need different binders, which Clayworks supply. A base coat and topcoat then follow.

    Any good plasterer can use their clay plasters to achieve a plain finish, and artisan plasterers would be able to create specialist textured or sculptural finishes.

    Self-builders can learn how to use clay plaster

    There are lots of resources and support available:

    1. Call the Clayworks technical team who can talk you through every aspect of how to apply the clay; the services, substrates, primers and the entire plaster build-up.
    2. Visit Clayworks’ website for techniques and tips.
    3. Clayworks offer one-day training courses for professionals and novice plasterers.
    4. Self-help resources, such as Using Natural Finishes, can help you learn about the process of applying clay and lime.
    5. There’s a network of recommended professionals who have been trained by Clayworks.

     

    Find out more

    Visit the website of Clayworks

    Follow Clayworks on Twitter

    Transcript

    Download a transcript of the interview with Clare Whitney

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  • HPH022 : Why Build a House with Straw Bales? – with Mark Saich from Green Building Solutions

    HPH022 : Why Build a House with Straw Bales? – with Mark Saich from Green Building Solutions

    Mark Saich from Green Building Solutions gives an insight into why straw bale building is becoming popular. He also addresses some of the issues that we may harbour around the safety and durability of this low impact and low carbon material.

    mark-saich

     

    Interview with Mark Saich

    Mark has worked in construction for about 25 years as a carpenter (joiner), in building control and also environmental health. Concerned about how buildings were being built, the amount of waste, the embodied energy of the materials in use, etc., he began to explore other options. Since 2000, he has been straw bale building and running training courses in the South East of England.

     

    Straw Bale Building is Nothing New

    Straw bale building was used extensively in Nebraska, US, in the late 1800s and early 1900s. Early settlers had to make use of the materials they had to hand.

     

    The Quality of the Bale is Paramount

    Although the bales used for construction are essentially regular bales (that you would see in a farmer’s field), they must be of good quality. This means the bales must be nice and tight, reasonably even-sized, dry, vermin-free and seed-free, etc.

    straw-bale-wall-going-up

     

    Avoid Damp and Dark Bales

    To a degree, choosing the right bales is a common sense undertaking. If a bale is damp it will smell damp and it will probably look darker and might even be blackening. These damp bales will also be heavier than a usual bale. Obviously experience of a dry bale is important to be able to tell this. Asking sensible questions of the farmer will also be helpful but it may still be a good idea to engage the services of someone who is experienced in straw bale construction.

     

    A Low Impact Foundation May be Possible

    Mark explains that for a load-bearing structure (essentially when you build out of bales just as you would if you were building with bricks) there may be an opportunity to lay a low impact foundation with less concrete, but this will depend on the ground conditions and the size and design of the building.

    sole-plate-ladder-foundations

     

    Problems Generally Only Arise When the Basics are Not Achieved

    Although Mark has seen examples of black mould and mushrooms growing on unfinished buildings, he says that it comes down to inappropriate detailing and weather protection during the build. A lot of the principles that need addressing during a straw bale build are the same as a when constructing with brick and block, timber, rammed earth, etc. Get it off the ground and stop rising damp coming up into the building (with the damp proof course, etc.).

     

    Moisture is the Biggest Threat to a Straw Bale Building

    As with any building, dealing with moisture is very important. Essentially in a straw bale building the damp proof course is protecting the timber ladder as much as anything. The other source of (external) moisture is rain, which is kept out by having either impermeable or semi-impermeable materials. While in a brick house this would be the bricks and mortar, in a straw bale house it might be timber cladding or lime render.

    Internally, a good ventilation strategy will be necessary to deal with moisture that builds up in the air from cooking food or drying clothes, etc. Using breathable materials – that have the ability to absorb and release moisture without it adversely affecting the longevity of the given material – can also assist in this process. Some examples of breathable materials include timber, sheep’s wool, wood fibre, lime plaster and straw bales.

     

    Straw Bales are Excellent Insulators

    Although the type of straw, its density and the quality of the build are all factors that affect the rate of heat loss, on average straw bales have a U value of 0.15 w/m2. Put into context, UK building regulations currently only demand 0.28 w/m2 (so a straw bale wall has roughly half the heat loss of a building regs compliant wall).

    bale-corner

     

    Bales Also Used to Form Prefabricated Panels

    Mark talks about the ModCell system called Balehaus, which claims a U Value as low as 0.13 w/m2 is possible for their 480mm straw product.

     

    Expect a Wall Thickness of 0.5m

    Typically with a rendered, plastered and clad (straw bale) wall, the thickness will be about half a metre. However, with building regulations likely to become more stringent in the coming years and most ultra low energy buildings demanding a lot of insulation anyway, this space is not out of the ordinary. Unless in a densely populated area, sacrificing an extra 10cm or so (in thickness) to use a low embodied material is not normally a big issue.

     

    Load Bearing Structures Rarely Reach Three Storeys

    Mark talks about non-load bearing structures – essentially where there’s a framed building with straw bales in between – and how with an engineered frame (that’s been tested accordingly) and infill panels, there is no limit to the number of floors of a building. With a load bearing structure, on the whole they are only single or double storey buildings. Mark says there are some examples with three storeys but it’s more like a half storey with a low eave (a chalet bungalow), that reduces some of the risk and some of the heights of the straw. This also makes better use of the materials because you are occupying half a roof space.

     

    If a Building is Structurally Sound, Resale Should Not be a Problem

    Although Mark had no information on whether straw bale houses can be valued alongside brick and block houses, he suggested that most people are fulfilling a dream to live this way and might stay in their new homes for many years. However, if a house is structurally sound and the building has been approved, inspected and signed off by building control, then getting a mortgage shouldn’t be a problem. Some mortgage companies will insist on a building warranty (which can be obtained from warranty companies). In the UK, Triodos and the Ecology Building Society both lend money at a preferential rate if you build to a good eco standard.

     

    Building a Straw Bale Home has the Potential to be Cheaper

    Trying to make a house ‘eco’ as an afterthought, by transposing materials for example, will probably mean that a straw bale build becomes more expensive. Designing the building from scratch with good environmental considerations can help bring the price down, particularly if you’re making your own clay plaster or if you use reclaimed materials, etc.

    straw-bale-sub-frame

     

    The Cost of Walls is Approximately 15% of The Build

    As the walls only account for about 15% of the final cost of building a house, the savings of a straw bale construction may not be as great as one might hope. So, comparing like-for-like brick and block house to a straw bale house, even if the straw bales were half the price, it’s not a massive reduction in the cost of the build.


    The Simple Things Will Lead to a Home That is Cheaper to Run

    Mark points out that designing a house to the size of your needs rather than to that of your greed will really reduce costs. Also, having a good thermal performance in the floor and the roof, and high performance windows that benefit from solar gain. Plus, installing high efficiency heating, lighting and hot water systems will all contribute to lowering the running costs.

    window-detailing

     

    Constructing with Straw Bales Lends Itself to a DIY Build

    Mark sums up building with straw bales as friendly and fun, and it ticks all the environmental boxes! He does recommend that it should be guided DIY, whereby you engage the services of someone who understands how to design buildings with straw and ideally someone with practical experience, too . Neglecting this could be costly for the building both in energy terms and longevity.

     

    Green Building Solutions

    As well as consulting on ecological building, Mark runs training courses on bale building (as well as spoon carving, clay plastering, etc.)

    mark-whiteboard

     

    Transcript

    Download a transcript of the interview with Mark Saich.

     

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    Ben’s Holiday Reading!

    Ben talks about reading a short story on climate change during his holiday. It blends facts from the past with a possible outcome of the future and is written by a ‘historian’ in 2074. It’s less than 15 pages and is well worth reading.

    The Collapse of Western Civilization: A View from the Future

    By Naomi Oreskes and Erik M. Conway

     

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  • HPH009 : Retrofitting a Victorian House to Passivhaus Standard #2 – with Alex Rice from Green Tomato Energy

    Alex Rice, Senior Engineer at Green Tomato Energy, explains that there are few technical challenges that remain when retrofitting a period home into a low energy building and it is a case of how you apply those solutions to the given building.

     

    Interview with Alex Rice

    Alex talks about the process of how his clients (often a husband and wife team) get started. He stresses the importance of trying to understand their needs and ideas, as well as discussing what is possible. This enables a clear brief to be written with objectives about which everyone is clear.

     

    Create and Stick to an Energy Target

    In many of projects undertaken by Green Tomato Energy they set targets to reach the Passivhaus (15kWh per m2 per year) or EnerPHit (25kWh per m2 per year) standards. Where listed buildings are concerned the target might be slightly higher due to the constraints. However, it is really important to nail down an energy target, because without knowing what you are trying to achieve in terms of energy it is nearly impossible to make the technical trade-offs that are required. This target guides the decisions that are subsequently made, thus changing your target practically changes the entire design.

     

    Understand the Building Itself

    Each building is unique and so understanding how it was originally intended to work is imperative. Alex highlights how Victorian dwellings function in a very different way from modern buildings in terms of how moisture moves around the building and the way they’re ventilated. Even the way people lived in them was different. In order to take that building as it was designed and make it work in a way that is almost completely different, you’ve got to have a really good understanding of the materials and the methods of construction that were used.

     

    Moisture is Death to a Building!

    Ben confesses he doesn’t really understand about moisture but he knows you don’t want to trap it. Alex explains that nothing kills a building more quickly than it being wet. He illustrates the point by saying a derelict building will stand for ages until the roof falls in and then it will disintegrate very quickly. Moisture causes wood to rot and bricks to undergo freeze-thaw damage. The primary aim of a building is to keep the building materials dry. Controlling sources of moisture from within and outside the building is crucial to the long term survival of any building.

     

    Where is The Moisture Coming From?!

    People are a source of moisture inside the building! They do things like wash and cook. They dry their clothes on radiators and water potted plants, etcetera. Then the other source is water outside the building including rain falling on the walls, water soaking up through the foundations, leaking out of gutters and coming in through faulty roofs.

     

    When Setting an Energy Target, Why Don’t We Always Go For The Best?

    The best target depends on the building and what you’re trying to achieve. For zero energy consumption, your house would be infinitely big which is clearly not possible. Trade-offs have got to be made between how thick your insulation is and what energy sources are available to provide heat. For example, if you have a Passivhaus that has very poor orientation so that you can’t get some south facing windows, then your insulation is going to need to be thicker in order to make up for that. There’s a trade-off between how much energy the building consumes, how expensive it is to build it, how much space it takes up and how costly it is to service the building, so the concept of Passivhaus is that you make the building envelope perform well enough that you can dispense with some of the techie bits of the building – parts of the heating system.

     

    The Passivhaus and EnerPHit standard are carefully selected

    The whole point of 15kWh per m2 per year is that it’s a point of minimum cost for that level of performance. The same principle applies to the EnerPHit standard, because in a retrofit project, getting the insulation in and getting the thermal bridges insulated is more expensive so it becomes cost effective to spend a little bit more on the energy and a little bit less on the building.  Those two points 15kWh per m2 per year and 25kWh per m2 per year were picked carefully as the best level of energy performance but built into those two numbers are assumptions about how much it costs and how difficult it is to achieve those standards, which is why when you go to things like listed buildings that number moves up, because it becomes cost effective and practically achievable to consume a bit more energy a year but make it much easier to build.

     

    Internal Wall Insulation vs Reduction of Floor Area

    It is Alex’s experience that you can put a surprising amount of insulation on the inside of a room and that once it’s all detailed in, you hardly notice it. When you’re putting it on it looks huge, but once it’s detailed in with the plasterwork, it really does disappear. The only exception is where space is already limited and therefore things like beds and wardrobes no longer fit into spaces that they previously did. There are higher cost ways of achieving the same level of insulation performance in less thickness using aerogel, vacuum insulated panels, etcetera. Generally speaking phenolic foam and those types of insulation materials are perfectly adequate and are the most cost effective choice for retrofit projects.

     

    Add Space as Part of The Project

    If you are retrofitting to Passivhaus or EnerPHit, then this is a major undertaking and thus this is the perfect time to extend your property. At this Lena Gardens Victorian terrace, a basement was dug out to provide space for the services and an extension at the rear enlarged the kitchen. So in this case there was more floor area at the end of the project.

     

    The Geometry of Old Buildings Make Insulating More Challenging

    One of the biggest challenges in a retrofit is working around the existing structure of the building. In a new build the walls can be made with the insulation in it already and it’s quite easy to design a thermally bridge free well insulated envelope. In an existing building there are often areas which are geometrically difficult to insulate.

     

    Removing The Timber Bricks!

    A lot of old buildings contain some timber in the walls. It was typical in Victorian construction that if something was brick-sized and brick-shaped then it would be stuck in the wall! This can only be assessed once the plaster is removed. It’s important to make sure the pieces of the building you are covering up are in a fit state to remain covered up behind insulation for the next few decades.

     

    Avoid an Adversarial Culture in Your Team

    Alex emphasises that communication amongst the team is key to the success of the project. The guys on site need to report issues as they arise and not feel that they will get an earful of criticism in return. As Alex can perform many of the tasks himself, he sees this as crucial in building up credibility with the tradespeople.

     

    Tradespeople Want to Work on a Passivhaus Project

    One of the indicators that a tradesperson is going to be good on this type of project is that they have previous experience. Tradespeople are becoming aware of this and they want to do a Passivhaus project because they realise it will be good for them to be known to deliver this level of quality. Passivhaus is becoming a hallmark of quality. Alex describes how after seeing a blower door test for air tightness for the first time, tradespeople often leave the site excited about the new knowledge they have learned.

     

    Alex Inspired By Ken Schaal From CommonWealth Solar in Virginia

    After studying for a degree in new and renewable technology at Durham University, Alex worked at CommonWealth Solar in the United States for Ken Schaal. Ken was part of the passive solar homes movement of the 1970s and had built a geodesic dome (using materials such as foam and concrete) for next to no money that also used practically no energy. Having lived in Victorian properties all his life, Alex describes this as an eye-opener as he always expected low energy buildings to be complex and expensive. Ken taught him that if you make a building well-insulated and airtight, you need the minimum of stuff to make it work.

     

    British Housing Stock is Very Different to America

    In the United States, buildings are often knocked down every 25-50 years to make way for the new designs. In the UK, the average life of a building is often a hundred years or more. Thus retrofitting is a major challenge for the future.

     

    Transcript

    Download a transcript of the interview with Alex Rice.

     

    UK Passivhaus Conference

    Having become more and more interested in a Passivhaus approach over the last few months, Ben Adam-Smith attended the UK Passivhaus Conference in Nottingham. There were some very interesting talks and Ben reveals that he has been taking notes on who he needs to speak to for future episodes!

     

    Is Cladding with Brick Pointless?

    Ben is confused about the options for his own project as he prefers more traditional aesthetics, yet he can completely understand why many Passivhaus buildings are finished with wood (which is far more sustainable) as the external surface. He wonders whether he just has to get used to it, as using an unnecessary layer of bricks on the exterior of a house is a waste of time and resources (even though he still likes the effect).

     

    Voicemail Message from Shauna Wyldeck-Estrada

    Shauna contacts House Planning Help to share information about her renovation of a Victorian house in Catford South. She talks about how she used sheep’s wool insulation in the loft and cellar, and how it has had an amazing effect on reducing her bills. A wood stove provides heat when required, making her central heating system redundant.

     

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