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  • HPH319 : Natural materials and healthy homes – with Tom Woolley

    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

    Please connect with us

    Subscribe, rate and review us on Apple Podcasts

    Like our Facebook page

    Follow Ben Adam-Smith on Bluesky

  • HPH285 : Developing plant-based building materials – with Judith Thornton

    HPH285 : Developing plant-based building materials – with Judith Thornton

    Dr Judith Thornton of Aberystwyth University explores how plant-based materials are being used in the building industry, and why they are so important for our future.

    Interview with Judith Thornton

    Judith works within the Department of Biological, Environmental and Rural Sciences at Aberystwyth University. She specialises in projects at the interface of plant science and material function, with her main interest being the use of plants as building materials.

    It’s about more than just building with straw or hempcrete

    Judith says that, historically, because of the finely honed skills required for each approach, there has been a tendency for the natural building industry to divide off into those that build with straw, and those that build with hempcrete. There are of course many other plant types that can be used, depending on the design criteria.

    She explains that we shouldn’t assume that we could build the whole project out of plants either, and nor should we assume that only one plant type will be suitable for each of the different building elements.

    Judith uses walls as an example, where because they provide the dual functions of structure and insulation, it might make sense to separate those elements out and use different materials. She says that otherwise, wherever you’re trying to get a particular product to perform multiple functions, you may well end up with significant compromises.

    Do your research

    Even within strawbale building there are different types of straw that can be used, but Judith says people rarely demand a particular variety, and generally just accept what they’re given.

    “I have yet to meet a strawbale builder who knew what wheat variety was in their building!”

    Historically the tendency is to use wheat straw, within which there are also a number of varieties, but sometimes barley straw is used. Barley straw however is far more prone to rotting than wheat straw, which Judith says should be a bit of a red flag when thinking about building with it.

    In Wales they have tested out building with miscanthus straw, which is a grass that can grow to three metres high, so is much tougher than wheat or barley, and presumably should be more resistant to breaking down.

    Judith says that there tends to be an assumption that strawbale buildings are inherently low energy, but that’s not necessarily the case. If they’re not built properly they can be leaky and rot, not very airtight and have high energy bills in the same way that any other building can.

    There is a lack of aspirational standards

    “We’ve got a regulatory system where we’ve got a fairly ineffectual stick and absolutely no carrot. So, ‘this will comply with building regs’, and people will say that as if that’s a good thing. Well, complying with building regs is as bad as you’re allowed to be before you get prosecuted. That isn’t an aspiration, is it?”

    Judith believes that there is a lack of incentive to build to the Passivhaus standard using low impact materials. She sees it is a combination of lacking aspirational standards and not valuing building enough as a trade, when it’s actually a very skilled profession and a challenging undertaking to build to Passivhaus standards.

    One of the key challenges with Passivhaus is getting the airtightness, and particularly concentrating on the junctions between different materials. It can be as problematic for man-made materials as it is with plant-based materials though. Particular care needs to be taken when designing details at junctions between timber and straw for example, where you might get some shrinkage in the plaster when it’s butted up against a timber frame.

    There would be no sense in trying to build an entirely plant-based building

    Judith thinks it would be ludicrous to even try. Using airtightness tapes as an example, she explains it as the law of diminishing returns: where a small amount of a very high tech materials provides a massive benefit. She says there is no point in obsessing about whether your strawbales are tied with polypropylene string or whether your airtightness membrane has got formaldehyde glue in it.

    “Partly because it makes almost no difference to the total carbon in the building and partly because it’s based on this completely false premise that natural things are safe and manmade things are dangerous. That simply isn’t true. But it’s a very commonly held environmental world view.

    “We do this weird moral balancing in the UK where we say, ‘I’ll fly abroad on holiday, but I did do my plastic recycling’. The whole plastic debate for me is seeking to shift blame to manufacturers as an alternative to examining our own behaviours.

    “It’s not rocket science. As individuals, we need to eat virtually no meat, we need to stop flying on holiday, and we need to insulate our houses.”

    Establish what the building industry needs

    Judith thinks that academics can have a tendency to come up with solutions for problems that don’t necessarily exist. So part of her role is having conversations with the building industry and the plant scientists to work out the areas that need new materials, and how the plant science community can contribute.

    One example is of insulating solid wall houses in Wales and doing that with vapour permeable materials. She says that hemp lime or another material mixed with lime is an excellent way of achieving internal wall insulation whilst minimising risks of interstitial condensation. It then becomes a question of analysing what it is that the plant material is doing in that mixture, seeing whether other plant materials are available, and then carrying out testing.

    Prevent biodegradable building materials from biodegrading!

    There are significant differences between various plant materials in how easily they biodegrade, and this will impact on the longevity of a building. The key thing is to stop moisture from getting in.

    Plants contain variable amounts of silicon and lignin in their cell walls which are protective against being broken down by microorganisms. Even different wheat straw varieties will contain different levels of lignin, which would impact on how quickly an individual piece of straw would rot if it were exposed to moisture.

    So one of the initial decisions to make when planning your build is as to how you plan to deal with moisture, and whether for example you have a vapour-permeable construction where moisture can diffuse into and out of the wall, or whether it will be a completely sealed envelope that relies on mechanical or window opening systems for moisture management.

    We will need to move to a plant-based economy

    Before fossil fuels we had a plant-based economy, and going forward this is something that we will need to revert to once again.

    Judith is involved in the university’s BEACON project, which looks at plants as products and how biorefining can help us move to a natural feedstock-based economy.

    “Everything we use on a day-to-day basis, be it building materials or plastics or everyday items, is going to need to be made out of plants and it’s a question of how we best do that.”

    Online Learning Resources

    Check out these sites for online resources, including webinars and training:

    Find out more

    Learn more about the work of BEACON

    Read Judith’s Blog

    Transcript

    Download a transcript of the interview with Judith Thornton.

    Please connect with me

    Subscribe, rate and review the podcast in iTunes

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  • HPH273 : A hemp house that also minimises plastic use – with Paloma Gormley

    HPH273 : A hemp house that also minimises plastic use – with Paloma Gormley

    Architect Paloma Gormley of Practice Architecture explains how versatile hemp can be as a building material, and how plastic use can be reduced on site.

    Copyright David Grandorge

    Interview with Paloma Gormley

    Paloma and Lettice Drake’s Practice Architecture made their name when they were approached to design a roof-top cafe above a car park while in the third year of their architecture degree. Not knowing where to start with appointing a contractor, they decided to build it themselves. From being incredibly inexperienced and using power tools they’d bought from a supermarket, they successfully constructed “Frank’s Cafe” which became an incredibly popular venue.

    Frank’s Cafe and Campari Bar, Peckham. Paloma Gormley and Lettice Drake
    Image Credit Andy Matthews

    Being closely involved with the construction process is a theme which has continued throughout their approach to architecture.

    Hemp is a versatile plant

    Industrial hemp is a plant within the cannabis family that has very low THC – the psychoactive element of the plant. It’s legal to grow in the UK with a licence and has a multitude of uses, with the fibre being used in rope and linen, the seed which has nutritional value, the bud which can be used medicinally, and the shiv which is the stalk of the plant that can be combined with clay to form hempcrete.

    Hemp also sequesters carbon more than most other plants. As it’s growing it sequesters carbon into the body of the plant and also into the soil.

    Paloma’s interest in using it as a building material began with a friend’s group, Hempen, that had set up a hemp farm in Oxfordshire. The friend had suggested using hempcrete as a building material for a three-storey London self build house they were working on, and it turned out to be a very practical material for the design. It was cast in-situ and infilled between a Douglas Fir frame.

    Image Credit Oskar Proctor
    Image Credit Lettice Drake
    Image Credit Oskar Proctor
    Image Credit Lettice Drake

    Drying time issues can be overcome by using pre-fabricated cassettes

    Paloma agrees that there can be an issue with drying and curing times when using hempcrete, depending on the binder that is being used. Some of the more reliable binders have a cement content, which isn’t ideal, but those that are pure lime can be more tricky to use as they can set too fast or slow or don’t hold.

    While it can set in 24-48 hours depending on the binder, the drying times can be incredibly long. They can average at around three months for the building to completely dry out depending on temperature and air flows, meaning secondary finishes can’t be applied during this time.

    Another limiting factor can be that it is not ideal to be casting hempcrete on-site during the winter period. There’s a risk that there can be too much dampness in the wall for too long before it has a chance to dry out, causing all kinds of problems.

    One solution is to take the wet process off-site. This means the drying can take place somewhere else and then delivered to site as dry cassettes ready to use. The benefits are a more streamlined construction process, with it being cleaner, less complicated, no time spent waiting about and all twelve months being available for building.

    Hempcrete Cassettes – Image Credit Paloma Gormley
    Image Credit Paloma Gormley

    Hemp is being used innovatively at Flat House, Margent Farm

    Margent Farm in Cambridgeshire are an organisation that are growing a 40 acre hemp farm. They carry out R&D and are developing a number of hemp-based bio alternatives to plastic products.

    The brief for the farmhouse on the site was that it needed to have a good connection with the landscape, have very low embodied carbon and to avoid plastic use wherever possible.

    Plastic in its various forms is prevalent even on buildings with high ecological credentials, being used as polyurethane rigid foam insulation, vapour barriers, sticky tapes, expanding foam, nylon thermal bricks and gaskets. It can also be other things invisible to the eye such as the wiring, ducting, pipes and vents.

    Hemp cladding has been used

    It wasn’t possible to achieve the elimination of plastic completely, because of barriers in terms of cost and also in terms of alternative products just don’t exist. But overall, Paloma said they did pretty well.

    They achieved it partly by returning to what is known as breathing construction. This takes moisture from the air inside a room, absorbs it into a wall and then breathes it out the other side.

    “There are many reasons why that’s a really good thing. It limits condensation, you can have a self-regulating moisture content in a room because if the moisture content in a space gets too high, it just gets pulled into the walls and then evacuated, and it means that when something goes wrong, you know it’s gone wrong because breathing construction generally involves a much more direct relationship of material.”

    Achieving a high level of airtightness hasn’t been a key concern on this project. The main priority has been to make a well thermally insulated, incredibly low embodied carbon building.

    “So, you always have to have a level of background ventilation which we used to achieve by just having slightly leaky buildings. Now we’re making incredibly airtight buildings and then making intentional holes, which I think is a funny logic in a way, because so much generally plastic goes into making incredibly airtight buildings and then we’re punching holes in them.”

    One of the products developed from the crop at Margent Farm is the cladding that they are using on the farmhouse. It is a hemp fibre with a sugar based resin derived from agricultural waste. They are combined, pressed together and baked in a heat moulding process.

    Image Credit Paloma Gormley

    The circular economy is informing design

    Cost concerns meant that aluminium windows were chosen over timber, and although it is a very high embodied energy material, the way it can be recycled means it fits in well with a circular economy way of thinking.

    Getting the foundations right was one of the biggest challenges on the project, and they opted for concrete foundations with a suspended timber joisted floor. Since then, they have been thinking of alternative options for future projects. One possibility would be screw piles, which are dependent on the type of soil you have and can’t be used in every situation. The thinking here is again about the circular economy, where these could be unscrewed and used on another project in the future.

    Another option they’re excited by is compacted hardcore such as flint or stone which could be sourced very locally.

    A cassette system was used for the walls, based around an eight by four sheet made in a factory as boxes, filled with hempcrete and dried. They were brought to site and erected within two days.

    Image Credit Paloma Gormley

    The roof was a straight forward joisted construction, with a wood fibre insulation.

    Image Credit Paloma Gormley
    Image Credit Paloma Gormley
    Image Credit Oskar Proctor
    Image Credit Oskar Proctor
    Image Credit Oskar Proctor
    Image Credit Oskar Proctor

    The Flat House led to the establishment of Material Cultures

    Material Cultures is a not-for-profit organisation that explicitly researches and explores these different materials in the realm of off-site construction. The aim is to make them more accessible, available and affordable. They are looking to start manufacturing at a larger scale, drawing on the model of the Flat House.

    Material Cultures are also working on research projects with two universities and are developing another prototypical building with architecture students at University of the Arts London, all feeding in to the broader research.

    “So, it feels very important to us that this project and these processes happen in a very reflective way, that we’re constantly learning and moving and developing thinking.”

    Find out more

    Visit the website of Practice Architecture

    Check out Practice Architecture on Instagram

    Find out more about the work of Material Cultures

    Learn more about the uses of hemp from Hempen’s website

    Transcript

    Download a transcript of the interview with Paloma-Gormley.

    Please connect with me

    Subscribe, rate and review the podcast in iTunes

    Rate and review the podcast on Stitcher

    Like our Facebook page

    Follow us on Twitter

  • HPH092 : Is Hempcrete a Good Material for Ecological Buildings? – with Professor Tom Woolley

    HPH092 : Is Hempcrete a Good Material for Ecological Buildings? – with Professor Tom Woolley

    Professor Tom Woolley from Rachel Bevan Architects explains what hempcrete is, how it is mixed and applied, and what the pros and cons of using it are.

    Tom Woolley

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