Tag: straw bale building

HPH319 : Natural materials and healthy homes – with Tom Woolley

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

Interview with Tom Woolley

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

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

The supply chain of natural materials is becoming far more robust

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

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

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

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

We need to stop using timber carelessly

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

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

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

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

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

Lime and clay can be great alternatives to cement

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

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

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

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

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

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

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

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

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

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

Hempcrete is an excellent material for managing moisture in a building

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

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

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

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

Emphasising eco-credentials can make mortgaging more challenging

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

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

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

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

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

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

Active House provides an alternative to Passivhaus

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

We don’t have enough building performance data

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

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

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

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

Find out more

Visit the website of Rachel Bevan Architects

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

Transcript

Download a transcript of the interview with Tom Woolley

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July 22, 2022
HPH089 : Can You Build to Passivhaus Standard Using Only Natural Materials? – with Bjørn Kierulf from Createrra
Bjørn Kierulf from Createrra explains how you can have the best of both worlds, using almost entirely natural materials to create a house that reaches the Passivhaus Standard.

Bjorn-Kierulf from Createrra

Interview with Bjørn Kierulf

Bjørn is an industrial designer and his wife is an architect, and together they run Createrra.

They have always been into building with natural materials, but now have adapted their approach to achieve Passivhaus Standard as well.

Natural Materials are Often Good Insulators

Most natural materials are fibrous and as such tend to be good insulators. They also have protection against summer overheating, though do need to be protected from humidity and moisture.

In order to reach high levels of insulation, however, a greater thickness of the material will be required (compared to artificial insulations such as aerogel).

Straw has the Ability to Take Structural Loads

When compressed, straw has very good insulation values and unlike most other materials also has the ability to take structural loads. While there are a number of load-bearing straw houses the structural calculations can be quite difficult which is why timber is usually used as well.

A further benefit is that it can be added to the compost heap, rather than landfill, when the building is demolished!

A Straw Bale House is Not a Flammable One!

Fire needs air, but straw bales are so densely pressed that there is no air to burn. When combined with a typical clay plaster it can have a 2-hour fire protection, meaning that even with a 1000 degree fire burning for 2 hours on the inside, there is no noticeable temperature difference on the outside.

Copyright Strawbuild

A Danger of Lime Render is High Water Absorption

Lime render is typically used by self-builders who are building with straw. Bjørn references the recent International Passivhaus Conference where the dangers of high water absorption in lime render were discussed. At Createrra they are looking into other options, such as industrial certified render plastered on wood fibre board which creates a thinner layer.

There is Often a Trade-Off When Using Natural Materials

Bjørn explains the difficulty of trying to get the right balance between using natural materials and materials that will last well under humid conditions. He sees this situation persisting for the foreseeable future, though predicting huge development and innovation in this area.

Natural Materials are the Basis of Innovative Products

Bjørn uses the example of a Swiss company who have experimented with using enzymes to treat the straw, thus giving it very different properties once it has dried out.

He also explains how a Danish company are using crushed mussel shells to make a foundation. The shells don’t absorb water and with air gaps they do have some insulating properties.

Much More Experimentation is Required for Natural Foundations

Bjørn feels they are still some way off an ideal natural foundation that he would recommend for clients. Hempcrete is another example he gives which, while appropriate for some areas, doesn’t have particularly good insulation values so wouldn’t create a thermally efficient building.

Airtightness is Crucial and Has Often Been Overlooked by Self-Builders

Problems are caused by humid air going through gaps in the construction and condensing in the structure.

One solution is to use a clay plaster, which is airtight, however it is difficult to achieve full airtightness because the plaster will always need to connect somewhere, such as where there are electrical sockets or beams going into walls.

Createrra are helping to develop a system using Ecococon straw panels where the airtight layer is on the outside of the straw insulation. This is in contrast to the typical way of doing things, where the airtight layer should always be on the inside in cold climates. These panels are wrapped in a recyclable airtight membrane and covered with wood fibre panels / ventilated façade. Early blower door tests have found that they meet the rigorous Passivhaus Standard.

The Ecococon panels are a combination of straw with wooden construction which are used to create the structure.

It is Difficult to Achieve an Entirely Natural Building

There are areas where construction using natural materials can be achieved easily, but areas like the foundations are more challenging. When also considering the whole of the interior, things like electrical cables being wrapped in PVC shows where there is still so much more that can be done.

Bjørn says that only around 500 materials were used in the construction of buildings at the beginning of the 20^th century, but now that figure is closer to 50,000. He sees the goal of having a building that at the end of its life can be put on the compost heap or recycled as being a greater challenge than solving the world’s energy crisis.

Createrra Have Completed 5 Passivhauses Almost Entirely From Natural Materials

The exceptions were the foundations and some of the roof membranes.

Feedback from their customers has been extremely positive, with perfect comfort levels maintained throughout the seasons. Bjørn thinks when people see the flat straw panels and the efficiency of the construction they see it as an attractive proposition, when perhaps they might not previously have considered straw.

Find Out More

Follow Bjørn Kierulf on Twitter

Transcript

Download a transcript of the interview with Bjørn Kierulf.

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May 9, 2015
HPH057 : Low Impact Living Affordable Community (LILAC) – with Joe Atkinson

Joe Atkinson explains how the LILAC cohousing community came together and why their project is affordable for everyone.

Interview with Joe Atkinson

Around 2005, Joe got quite interested in fuel depletion and climate change. At the time, Joe had a nice job in IT and was getting paid well but felt that his life wasn’t very fulfilling. He was looking to get involved in something that would provide this fulfillment, and be in line with his ethics.

Eco-building Can be Really Simple

Joe did a Masters in Architecture at the Centre for Alternative Technology in Wales, at Machynlleth which he found absolutely fascinating. Being a bit of a techie, he really liked the technical side of the course and the physics behind how buildings work. This got him really interested in eco-building and he feels that a lot of it is actually really simple and backed by common sense. Instead of constructing thermally leaky buildings, we should be building sensibly.

How Joe Got Involved in LILAC

Joe went to an event where some of the members of LILAC (it was previously known as Leeds Eco Village) had a stall and were trying to recruit new members. Joe was at a point in his life where he was looking for somewhere to live. LILAC appealed to him as it was community of people who were building eco-houses that he would be able to afford. It was a no-brainer for him from that perspective and he got involved.

Being on the Board

When Joe joined, the group was really keen to recruit people on to the board. As Joe is the kind of person who commits totally to something new that he gets excited about, he decided to join the board.

Being on the board meant taking legal and financial responsibility for the project collectively with the other board members. Once Joe joined, he found his own little niche as the person who is a good team-builder. The board at the time was populated by lots of people who were really dynamic and making stuff happen, and his supportive role on the board really helped things along and played to his strengths.

Making Community Decisions

The board needed to think about how the whole community functioned and to avoid a two tier decision making system between the board and non-board members of the community. To address this concern they had an away weekend where an external facilitator came in and they did a whole community visioning and strategic planning exercise. They discussed the whole community’s goals and looked at different options for how to get there. Smaller task teams were set up to look at particular aspects of the project such as their relationship with the existing community, recruiting members, publicity and so on.

Joe joined the group that was to liaise with the professional team- the quantity surveyor, the project manager and the main contractor. The group went through a tender process to appoint a contractor.

Developing a Relationship with Leeds City Council and the Existing Community

The group had been in discussions with the Asset Management Team at Leeds City Council about various sites around the city and looked at two that were very suitable. It took the group a while to develop a relationship with the Council because when they first approached them, they probably came across as a bit of a rag-tag bunch of optimistic, well-meaning do-gooders who wanted to build some eco-topia. It wasn’t until they came back to them with a project manager and a serious business plan that the Council started to really take them seriously as a credible group who they could sell the land to.

They ended up choosing the site in Bramley, where they did a community consultation with the local residents. The community really liked the idea of what they were trying to do which gave the group a really good feeling about choosing that site.

LILAC- (L)ow (I)mpact (L)iving, (A)ffordable, (C)ommunity

LILAC is an acronym and stands for three main elements- Low Impact Living, Affordable and Community. The Low Impact Living element comprises of buildings built using the fabric first approach, an airtight construction with mechanical ventilation with heat recovery and the use of renewable materials such as timber, straw bale, lime render and lime plaster and triple-glazed windows. There is solar PV on the roof and solar thermal for the houses but not for the flats. They have used the Passivhaus approach, and are not far off from it, but haven’t spent the extra money to get the accreditation. They also have fewer car parking spaces- there is half a car parking space per home and two secure bike parking spaces. They have also set up community agreements for lots of other different aspects like sub-letting agreements, the car policy and the installation of electric car charging points.

The LILAC Mutual Home Ownership Society

Joe explains how the affordability model of LILAC is achieved through their legal and financial structure which is called The Mutual Home Ownership Society. It is essentially a housing co-operative and it uses a new financing model unique to Britain, as each member is effectively buying shares in LILAC Mutual Home Ownership Society Limited.

The total project cost is divided proportionally between each of the twenty homes, with each home representing the notional build cost for each unit, e.g. where the four bedroom units are more expensive to build than the three, two and one bedroom units. The amount that people pay to live there is related to their earnings. So all the members pay thirty five percent of their net income and the amount that relates to determines the exact size of their home size.

Once the debt associated with your flat or house has been paid off, you drop down to just paying ten percent of your net income. At that point you’re just paying a small amount as a service charge or ground rent. If you had a normal leasehold, you’d always be paying a small amount for things like insurance and management fees, etc.

The group is decoupling the value of the homes from the housing market, and that’s intended to keep these homes affordable in perpetuity. So they will always have the same ratio to earnings. Living at LILAC isn’t about investing in property; it’s about creating affordable housing as a legacy of the project and about buying the service of a home. It’s about homes as shelter, not as a nest egg or an investment.

LILAC is about Creating Good Quality Affordable Housing

According to Joe the process has worked so far and they are keen to support other groups who are interested in this model. At LILAC, they are not creating social housing, but affordable good quality housing. Joe can’t imagine anywhere else where you can get to live in an eco-house with all this amazing community and it’s affordable and you get to own it. This is potentially a model for anyone who is excluded from home ownership for whatever reason.

They have an active waiting list and they are receiving new applications all the time. This gives the current members an added level of security. If a member were to lose their job and couldn’t afford to live there anymore, there’s a whole process that takes place before they have to move out. And if at the end of that process they still have to move out, there is a waiting list of people that already want to buy your shares and move in.

Membership by Consensus

Everyone who lives at LILAC- apart from a couple of the very early founders – has had to apply to join. Because the group operates a consensus decision making model, everyone in LILAC has the right to veto someone applying. When Joe’s partner moved in, she had to write an application too and there was a period when somebody could’ve voted against her moving in. She sailed through with flying colours, recounts Joe happily.

Living in Cohousing Comes with its Own Challenges

Joe feels that it has been quite interesting going through a process where you have to prove that you can afford to live at LILAC because the affordability model relies on everyone declaring their financial situation. Although they now have a finance task team who look at all the finances, previously applicants had to submit their application with their financial information to their future neighbours which could be quite uncomfortable.

Living in an intensive cohousing community requires you to adapt and change the way you think. It can be really nice and sociable, but at times overwhelming. One of the real strengths of the cohousing design is that you have got your own place and you can retreat to it if you need to. But when you’re ready to come out, you’ve got a whole community there waiting.

Everyone at LILAC has been very supportive and open minded and have a real willingness to learn about living in a community and to learn about themselves as well. Living in cohousing challenges you in ways that you might not expect- it is a bit different to living in a traditional street in Britain. Joe admits that there have been a lot of challenges so far and there are likely to be more in the future, but they look forward to them.

Find Out More

LILAC’s website

Transcript

Download a transcript of the interview with Joe Atkinson.

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June 11, 2014
HPH042 : Can a Straw Bale House Reach Passivhaus Standard? – with Fran Bradshaw from Anne Thorne Architects
Fran Bradshaw from Anne Thorne Architects shares her experience of building an ultra low energy home using natural materials such as straw bales, lime render and clay plaster. The house is also aiming for the Passivhaus standard.

Interview with Fran Bradshaw

Fran Bradshaw was a builder before she became an architect but she’s still very much interested in the practical side of things. A lot of the work she does at Anne Thorne Architects has a focus on sustainability and community-based work.

This episode is about a straw bale house that she’s building for herself in Norfolk, UK.

Straw Bale Building Allows People to Get Involved

Fran got inspired to build her own house with straw after working on a project for Haringey Council.

Local people helped both design and construct the eco-hub, which Fran describes a wonderful experience: “It was really exciting being on site and just seeing how enthusiastic people were and what a great community benefit it was.”

Volunteers help construct an eco-hub in Lordship Park

Natural Buildings Feel Different

Upon completing the eco-hub, Fran noticed that lots of people commented on the quality of the environment.

The acoustics, humidity and the colours are all very different in a building constructed of natural materials – people liked this.

The finished eco-hub (credit: Rae Parkinson, Straw Works)

Getting the Details Right is the Biggest Challenge

While there have been straw bale houses in mainland Europe that have reached Passivhaus standard, there is yet to be one in the UK.

The challenge is in turning what is a rather chaotic building material into something that is actually very precise, because to achieve the Passivhaus standard all the details on all the joints have to be very neat and carefully airtight.

The timber frame goes up on Fran’s house

The Team Must be Led by Someone Experienced

Although one of the reasons Fran chose to build her house with straw was to involve her friends, she leveraged the experience of Straw Works.

So guided by one or two experts, the rest of the team members just need to be enthusiastic and prepared to do a little bit of physical work.

Barbara Jones from Straw Works examines the quality of a bale

A Reed Thatch was Chosen for the Roof

The site is very close to the Norfolk Broads and Fran discovered that reed thatch was being cut a mile away.

She describes this as too tempting: “Yes, it’s just a very good roofing material. It’s very durable. It’s got a natural insulation value so there was no reason not to use it. I mean it’s more expensive going with thatch rather than clay tiles or something and that was my extravagance really.”

Reed Consistency is Important

In order to thatch well, the reeds need to be the same strength, the same length and have the same diameter.

This is partly to do with how well and methodically the reeds are cut, which is why reed cutters are given long contracts to tend a certain patch.

The Airtight Layer in the Roof is Below the Thatch

The thatch is on fireboard which is moisture permeable but airtight. It’s taped at the joints so that the airtight layer is just underneath the thatch.

Warmcel – recycled newspaper insulation – then goes in between the plasterboard and the underside of the fireboard.

The Floor is a Reinforced Raft

Fran says the connections between the walls and the floor are always tricky to get right and, as this project is aiming for the Passivhaus standard, she opted for a reinforced raft.

While there was a level of compromise here it is quite economical on concrete and it gave Fran the opportunity to employ a local contractor (whereas many parts of this build have needed specialists).

Due to Timber Penetrations the Airtightness Layer is on the Outside of the Wall

Normally the airtightness layer would be on the inside of the house to avoid warm, moist air from the room going into the wall fabric.

As there’s timber inside and the straw is outside the timber frame, in this case it would have been very difficult to make the airtight barrier work well (because there are timber penetrations and quite big bits of timber).

After discussing the best approach with their airtightness expert Paul Jennings, they decided to use the outside layer of render as the airtight layer.

So the concrete slab is the airtight layer in the ground which connects to the lime render on the outside of the straw walls and then to the fireboard on the roof.

A Theoretical Risk has been Managed

There is a theoretical risk to having the external lime render as the airtightness layer as Fran explains: “Inside you’ve got clay plaster and that effectively is airtight as well but for instance at the windows where it’s all taped it’s on the outside, so theoretically you could get moist air going at the junction between the internal plaster and the window and condensing within the straw.”

They are pretty confident this won’t be a problem because all the materials are moisture permeable and hygroscopic as well, and the MVHR ventilation will be operating at the coldest times.

Moisture monitors will also provide on-going data, so should any issues arise they can be addressed.

The Clay Plaster and Lime Render Will Need to be Maintained Every So Often

As the lime render is the airtight layer, any cracks that appear could affect the airtightness and thus the energy efficiency of the house.

However, this is just part of using these materials – these cracks will need to be repaired. Fran is expecting this at the end of the drying out process but is not sure how often the maintenance will be after that.

Nearing completion!

There’s a Role for an Airtightness Geek!

Working with these kind of materials and trying to achieve high levels of airtightness, Fran can definitely see the need for a ‘very precise airtightness geek person’ who has a close eye on all the details as the build progresses.

This could develop within building firms or be a role that is taken on by a broader group of people.

Prepare for the Key Moments

There are certain key moments where you’ve got to be absolutely spot on, so find out where these are.

Planning for those moments and making sure that there are the right people around at the time will stand you in good stead.

You Can Always Do Things for Less BUT . . .

While Fran knows that there are always ways to cut costs, she derived great pleasure on this project from being able to work with people who she knew were going to do a really lovely job.

Although she may have paid a little bit more it’s been worth it and she still believes it’s been reasonably economical given the materials used.

Invest in People

Look carefully at what people have done in the past and trust your judgement about them.

For work like this Fran is not in favour of endless competitive tendering. On the whole she’s selected people who she enjoys working with and who charge a reasonable rate for what they do.

Passivhaus is a Language We All Understand

The first air test of Fran’s house recorded a figure of 0.9 air changes per hour.

She still hopes to meet the Passivhaus standard: “I’d really like to certify it because it’s a language that we all understand. Either you’ve achieved it or you haven’t. If we don’t achieve it, that’s okay, we’ll have got very near it and the difference in the building performance between not quite achieving it and achieving it is really quite small. It’s just very exciting for me to have this house and this opportunity to live in it.”

Find Out More
- Anne Thorne Architects
- Read their blog all about Fran’s straw bale house
Transcript

Download a transcript of the interview with Fran Bradshaw.

Our Question for the Comments Section

Have you managed to incorporate natural materials in your project? And if not, why?

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February 18, 2014
Designing and Self Building an Affordable Straw Bale House

We often hear that house affordability is what’s stopping first time buyers from getting onto the property ladder. However could self build deliver more affordable solutions? This case study illustrates that there are savings to be made, although there will also be challenges to overcome.

In fact when Brian Waite was looking to build a house [in the UK] for his retirement it was the plot of land that was so difficult to find: “Plots seem to be cheaper when they’ve got a house on them, which is a crazy situation! So we bought a plot with a house on it, but the house was just that little bit too good to knock down.”

The house that they bought came with planning permission for an extension where the garage was and then a new garage could be built the other side of the driveway. Brian thought it would be a simple matter to have a smaller extension and a slighter bigger garage (i.e. the straw bale house) but the planners didn’t agree.

So their new house is actually not their house but Brian’s office and a smaller scale version of his prototype. It was after converting his former home, a medieval barn in Kent, that Brian had the idea for it.

He liked straw as a material because it was a low cost, sustainable option that would allow him to reach the high levels of insulation he desired (without having to use a synthetic material with a high embodied energy). Brian couldn’t understand why it wasn’t used more often.

After looking at other straw bale houses and not liking them, he decided to design his own!

This may not be a path for everyone but Brian was a structural engineer and this clearly gave him an advantage when it came to working out what he wanted to do: “I just couldn’t stomach load-bearing straw bales because logic tells you that in time they will lose some of their integrity and settle. That means that the roof loads in a normal straw bale house would be transferred straight onto the plaster and render.”

He was keen to keep the design simple and used a bowed timber A-frame, like a medieval cruck.

These single beams can be varied in length and height as required but the whole interior is free of structural restrictions.

Brian reflects on the simplicity of the build by saying that the most expensive piece of equipment on site was a cement mixer. There was no call for a crane either – a £20 hand winch did the job!

“I was 68, 69 when I built it and I did it entirely on my own, except for the lime plastering. If I can do it, definitely a younger person can.”

Brian also devised a system to air the bales and keep moisture content under control. Normally a large eaves overhang would provide the necessary weather protection but he had relocated to Cumbria where the rain is often horizontal!

“I don’t know what size of eaves I would need to protect the walls but in my case the tiles cover every bale so there’s no worry about weather protection on an exposed site, but I also exploit a chimney effect. Because the tiles come down to within a metre of the ground, the air entry is behind the gutter at that level and the exit is about 7m up, so you’ve got a very strong chimney effect that I’ve used to draw air over the exterior of the bales (underneath the tiles and over the exterior of the bales) to wick out any moisture.”

The bales are rendered with lime on both sides.

The bales don’t have to be laid like bricks as they just slot in. Out of 380 bales used Brian only needed to adjust the length of two or three. He also had to work his way around the Cumbrian weather when it came to putting them in. Although originally intended to go in from the outside, he had to devise a way of doing it from inside, which actually worked better in the end.

The cost of this kit would be somewhere around £30,000 (US$50,000) and Brian has registered the design and has patents pending on some elements of it.

He reckons this could be an affordable solution for first-time buyers, although the land would then become the most significant cost. Find out more about Brian Waite via his website.

September 10, 2013
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.

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.

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.

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).

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/m²is 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.

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.

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.)

Transcript

Download a transcript of the interview with Mark Saich.

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