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  • HPH397: Sheep’s wool insulation and other natural fibre options – with Mark Lynn

    HPH397: Sheep’s wool insulation and other natural fibre options – with Mark Lynn

    Mark Lynn from Eden Renewable Innovations explains how sheep’s wool insulation is made, outlines the pros and cons, and suggests how it is best specified and installed. He also shares some common traits of natural fibre insulation as a category.

    Interview with Mark Lynn

    In this episode Ben Adam‑Smith sits down with Mark Lynn, Managing Director of Eden Renewable Innovations and Chair of the Alliance for Sustainable Building Products (ASBP). Together they unpack what natural‑fibre insulation really means, why sheep’s wool insulation is gaining traction, and what homeowners and builders need to keep in mind when specifying and installing products such as Thermafleece.

    Natural fibre insulation is any building insulation made from renewable plant or animal fibres

    Mark defines natural‑fibre insulation as any product whose primary component comes from a biological source – sheep’s wool, wood fibre, hemp, jute, cotton, flax and cellulose are just some examples. These materials can be used alone or blended, and they are often processed into batts, rolls, rigid boards, or loose‑fill. Because the raw element is renewable, the embodied carbon of the product is typically far lower than that of conventional mineral or synthetic insulation.

    “Natural fibre insulation is any building insulation that’s made from or using natural fibres.”

    The variety of fibres gives designers flexibility: wood fibre offers rigidity, hemp provides high tensile strength, while wool excels at moisture regulation. Understanding the source material helps you match the product to the building’s performance goals.

    Moisture‑buffering is a unique strength of natural fibres

    At the molecular level, natural fibres carry electrical charges that attract water molecules. Rather than allowing water to pool as a liquid, the fibres hold it in a solid‑state “bound” condition. This limits the risk of mould and rot, because the water cannot act as a universal solvent that accelerates decay.

    Sheep’s wool, composed of the protein keratin, is especially adept at this exchange, absorbing humidity when the indoor air is damp and releasing it when conditions dry out. The result is a more stable indoor environment, particularly in climates where indoor humidity fluctuates dramatically.

    “When the water molecules adhere to the natural fibre the way they do, they can’t behave like a liquid.”

    Breathability is not a substitute for ventilation

    Mark cautions that a breathable fabric does not eliminate the need for a proper ventilation strategy. Inside our homes we generate moisture through our activities (showering, cooking, doing laundry, etc.) so there needs to be a constant exchange of stale air being replaced with fresh air. In Passivhaus homes, for example, mechanical ventilation with heat recovery (MVHR) fulfils this role. The insulation’s ability to buffer humidity is therefore an additional benefit rather than an excuse to forget about ventilation.

    Good design requires adequate ventilation, sufficient vapour openness (the ability of water vapour to pass through the material), and the inherent moisture‑buffering capacity of the fibre. When these work together, the insulation remains effective without becoming saturated.

    Condensation risks can be modelled

    Tools such as WUFI can help model moisture, taking into account climate data, wall build-ups, and internal conditions. This will then identify potential condensation risks and allow them to be addressed at the design stage. Ignoring this step can lead to interstitial condensation and the knock-on effects of mould and damp, which in severe cases could even cause structural damage.

    Three main forms of natural‑fibre insulation: flexible, rigid, and loose‑fill

    1. Flexible insulation – often supplied in slabs, batts or rolls that can be cut to size.
    2. Rigid wood‑fibre boards – medium‑density panels that can be fixed to walls or roofs, offering structural support.
    3. Loose‑fill – shredded fibres (typically recycled newspaper or fine wood) blown into cavities, ideal for irregular spaces.

    Sheep’s wool is available both as flexible batts and as rolls, giving installers the convenience of a rockwool‑style product while retaining the natural advantages of wool.

    Sheep’s wool insulation is easy to install in a loft

    We should be taking advantage of all natural fibre insulations

    When asked about how we choose a natural fibre insulation, Mark suggests that it’s actually better to support the whole category. All natural fibre insulations will have their strengths. For example, when insulating a loft a roll of sheep’s wool may be the simplest and quickest to install.

    “We’ve got to use the right type of the right resource in the right way, and that really involves a whole mix of materials.”

    The ASBP’s Natural Fibre Insulation Group publishes a comparative guide that helps architects weigh factors such as thermal performance, acoustic qualities, fire resistance, and cost. Using that data ensures the selected material aligns with the building’s functional and regulatory needs.

    The market for natural‑fibre insulation is growing

    Historically, natural fibres accounted for roughly 1 % of the UK insulation market, compared with 10–15 % in France and Germany. Since the pandemic, consumer research into health‑focused homes has accelerated adoption, and manufacturers report strong year‑on‑year growth.

    Mark predicts that reaching the 10–15 % threshold in the UK would make natural fibres a credible mainstream option, offering homeowners greater choice without sacrificing performance.

    “These aren’t quirky eco products, they are part of the insulation mix.”

    Shearing a sheep for its wool

    Manufacturing sheep’s wool insulation

    Sheep’s wool delivers acoustic performance comparable to high‑grade rockwool

    Thermafleece UltraWool, a flagship wool product, achieves the same sound‑absorption ratings as a 45 kg/m³ rockwool product, despite being only 32 kg/m³. The lower density reduces dead‑load on the structure while still dampening noise, making it a compelling option for residential lofts and office partitions where acoustic comfort is a priority.

    Fire safety is addressed through mineral fire retardants, not by claiming non‑combustibility

    All natural‑fibre products, including wool, incorporate a mineral fire retardant that encourages charring rather than rapid flame spread. While they are not classified as “non‑combustible,” they meet Part B of the Building Regulations for the intended applications.

    For projects that require a non‑combustible rating—such as certain high‑rise or public‑access buildings—additional layers or alternative materials may still be necessary.

    Insulating a barn with sheep’s wool insulation

    Cost is competitive when viewed against performance and lifespan

    Mark notes that comparing wool to a cheap fiberglass roll can be misleading. When matched against high‑performance mineral products, the price differential narrows, especially when accounting for its long life (60 + years) and the reduced need for replacement.

    A typical loft installation with Thermafleece can be completed for under £1,000, and the energy savings often recoup the investment within five years.

    A thin layer of insulation can make a big impact

    When dealing with existing buildings, for example a period property with a solid wall, a thin layer of internal insulation can make a big impact to comfort and keep costs down. It must however be a continuous layer, eliminate thermal bridges and be installed well. One advantage of this thin layer is that you’re far less likely to have moisture build-up in the fabric, but you’ll feel a noticeable benefit to the comfort of the property.

    Environmental benefits extend beyond the insulation itself

    Sheep’s wool used in insulation is often sourced from the coarse, dark fleece that has limited textile applications, turning an agricultural waste stream into a high‑value building product. The polyester binder incorporated into the rolls is made from recycled plastic bottles, further closing the material loop.

    By sequestering carbon in the keratin fibres and reducing the demand for petrochemical‑based insulation, wool contributes to lower embodied emissions and supports rural economies.

    “We’re buying a reasonable proportion of the UK wool clip… adding value to the rural economy.”

    Find out more

    Other resources mentioned

    What is a healthy building product?

    Should you specify uPVC windows?

    Introducing the circular economy to housing

    What is the problem with plastic?

    How are building regulations made?

    How natureplus helps you identify sustainable building products

    What is wood fibre insulation?

    How easy is it to insure a natural building?

    Transcript

    Download a transcript of this episode.

    Please connect with us

    Subscribe, rate and review us on Apple Podcasts

    Follow Ben Adam-Smith on LinkedIn

    Follow Ben Adam-Smith on Bluesky

  • HPH193 : Should you specify uPVC windows? – with Simon Corbey from ASBP

    HPH193 : Should you specify uPVC windows? – with Simon Corbey from ASBP

    Simon Corbey from ASBP shares some of his research into the costs and life cycle of plastic windows and suggests some considerations for self-builders.

    Interview with Simon Corbey

    Simon Corbey worked as a chartered surveyor in the ‘90s, and went on to become a specialist in natural paints for London’s first eco builders’ merchant, Construction Resources. He has also worked for BioRegional, the Sustainable Development Foundation, the Good Homes Alliance and the Alliance for Sustainable Building Products (ASBP). Last time we spoke to Simon, he talked to us about healthy building products.

    We should question the chemicals in uPVC

    Simon Corbey has been working on behalf of the ASBP to compare plastic and timber windows. Consumers tend to be more concerned with how windows will look and last than where plastic comes from and the issues around it. Simon remarks that plastic windows are manufactured widely in the UK, but these impacts are not really considered, adding, “I do think that there’s an opportunity for the UK to develop their building physics and approaches to making windows.”

    Simon notes that plastic windows appeal, as they are generally cheaper and available in a range of styles. He describes the marketing as aggressive, adding, “It’s well funded, of course. It’s the petrochemical industry.” Plastic windows contain a range of chemicals but no research has suggested a negative effect on indoor air quality. The window itself may be benign, but Simon has also been researching product manufacture and life cycle.

    Manufacturing chlorine is hugely energy intensive

    Simon explains that uPVC (unplasticized polyvinyl chloride) contains chlorine. Used in swimming pools and our water supply, it’s common enough to not raise concern. However, he explains that its manufacture has an incredible impact on the environment.

    Simon estimates that producing 80% of the UK’s chlorine uses more electricity than Liverpool. Production of PVC in Europe in 2015 used 8.6 million tonnes of chlorine. “So it’s hugely energy intensive,” says Simon, adding, “From a life cycle analysis it’s a terrible, terrible thing.”

    Simon’s research shows the hidden costs of uPVC windows

    Simon has further researched Ineos, who produce most of the UK’s chlorine. Describing it as “a very murky world,” he says he feels motivated to bring this to people’s attention. The site of the Ineos plant in Cheshire is of particular concern. Simon describes how Ineos were caught dumping mercury into the Manchester Ship Canal in 2014 and the land contains a dump once used to “make everything from nuclear weapons to World War II stuff”.

    Previously owned by ICI, the dump was linked to toxic chemical leaching and reports of ill health in the early 2000s. Today, explains Simon, if you look at the Land Registry, this dump apparently has no owner. “There is a completely toxic dump just there which the council don’t own,” he says. “Ineos have somehow redrawn the lines of their site and conveniently they don’t own it any longer.”

    Timber windows struggle to compete on price and marketing

    Despite their significant environmental price, plastic windows remain cost effective for manufacturers. The price of oil and gas is still low, making the raw materials cheap. The process of gathering timber, processing, sawing and milling it is quite energy intensive in comparison and the end product is heavier to transport. All of this adds to cost.

    Simon further points out that the UK timber industry is quite fragmented, containing many different disparate interests. Conversely the plastics industry markets products with “one voice”, typified by slick campaigns, such as that for Everest windows. Moreover, Simon describes it as quite litigious, recalling a threat of court action when his former employer persuaded a Scottish Housing Association to cancel their order for plastic windows.

    Plastic windows may not outlast timber

    There is a perception that timber windows will rot, requiring repeated maintenance, while plastic is assumed to be tougher. Simon questions these preconceptions. While acknowledging that timber windows have a finite life cycle he points out that plastic windows are prone to yellowing after a while. Simon himself has 120-year-old timber windows, which are “going strong”. “They’re a bit leaky,” he says, “but they’re okay as far as I’m concerned.”

    Other options for window materials do exist. Simon recommends considering factors such as product life cycle and building location. Aluminium is very durable but highly energy intensive; composite timber and aluminium windows are one alternative.

    The quality of UK timber windows is improving

    Windows are an essential part of the building fabric’s performance. With improvements in building science, double glazed and triple glazed windows are appropriate for new builds and both plastic and timber windows can achieve Passivhaus Trust certification.

    Where good indoor air quality is maintained by natural ventilation, windows must function well, being easy to open and clean. There have been some issues of quality with some timber windows but Simon sees this improving, following the standard of European and Scandinavian manufacturers.

    Recycling plastic windows involves additional expense, chemicals and risks

    The Scottish Civic Trust suggests that the recycling rate for windows might be 3% and according to the Green Guide, BRE suggest that the UK average is about 15%. However, Simon suggests the many issues with recycling, such as the chemicals and risks involved, make that figure optimistic.

    The formulation of plastic has changed quite a lot since the ‘60s and the industry has made great attempts to clean itself up. Substances considered by REACH to be of very high concern, such as lead and cadmium, are being phased out although tiny quantities are still allowed.

    Plastic is worse than wooden windows in a fire

    Simon believes that toxicity is a huge issue. He confirms that plastic windows pose a greater risk than wooden ones in the event of a fire and believes that more research is needed. However, currently all the testing institutes are very busy “as a result of Grenfell”.

    Simon notes that in the USA, The Healthy Building Network has liaised with the Fire & Safety community to argue for a complete halt to use of plastic products. Likewise, the ASBP has initiated contact with Kent Fire and Rescue and the London Fire Brigade. As Simon explains, “there is some research underway but it’s early doors, I would suggest, this type of testing.”

    Industry and consumers are moving away from plastic

    Techniques and attitudes continue to change. Acetylated wood is an example where window science has improved. This process basically uses vinegar to extend the maintenance life of timber to over 60 years.

    Simon notes a growing interest in health and wellbeing, as well as a global campaign against plastics. He summarises, “I think at ASBP we’re trying to suggest that as a society we’ve just got to start using less plastic through and through, in all the things that we do and windows being one of those things.”

    Find out more

    Visit the website of the Alliance for Sustainable Building Products (ASBP)

    Follow the ASBP on Bluesky 

    Transcript

    Download a transcript of the interview with Simon Corbey

    Please connect with us

    Subscribe, rate and review us on Apple Podcasts

    Like our Facebook page

    Follow Ben Adam-Smith on Bluesky

  • HPH167 : What is a healthy building product? – with Simon Corbey from ASBP

    HPH167 : What is a healthy building product? – with Simon Corbey from ASBP

    Simon Corbey from the Alliance for Sustainable Building Products (ASBP) shares some thoughts on what makes a healthy building product.

    Interview with Simon Corbey

    Simon Corbey became a chartered surveyor in the nineties, but later decided he wanted to do something more meaningful and so volunteered at Construction Resources, London’s first eco builders’ merchant. During his five years there he worked his way up to being a specialist in natural paints. It was whilst in this role that he came into contact with people who had developed health issues using conventional materials and who were looking for better options.

    Since then he’s worked for BioRegional, the Sustainable Development Foundation, the Good Homes Alliance and the Alliance for Sustainable Building Products.

     

    Not all materials affect people in the same way

    As we are all different, we all react to products in different ways.

    Simon comments: “What will affect one person, because they’re chemically sensitive for example, just won’t affect another person. So, unfortunately, it gets quite complicated, quite quickly.”

     

    If in doubt about a product, perhaps avoid it

    The precautionary principle is a good rule of thumb.

    If you don’t really know what’s in a product and you can’t get hold of a full statement of the contents, and if there’s a slight doubt in your mind, it’s probably better not to use it.

    Instead, find a product that you can trust, where there is a full declaration of contents.

     

    A healthy building should address a number of disciplines

    A healthy building is a complex matrix and includes disciplines such as acoustics, daylighting and ventilation.

    Source control – controlling the amount of chemicals that come into a house in the first place – and effective ventilation are fundamental to creating a healthy indoor environment.

     

    Natural products are not always healthy

    It could be argued that all products are ‘natural’ because they’re made from materials that naturally occur on our planet.

    Increasingly natural materials are processed and then joined up with other products to make a system. At this point, it becomes harder to classify that system in regards to its health and wellbeing benefits.

    Simon says: “There are plenty of products, natural paints for example, that have quite high levels of VOCs within them, whether it be dryers, whether it be the oils themselves.”

     

    Healthy products often have additional benefits

    Simon uses wood fibre insulation as an example of a product that has benefits beyond its main purpose. For example, it’s a waste product that’s binded with steam and has no additional glues. This makes it a great product to handle and cut.

    As its dense, it is good is alleviating the effects of overheating.

     

     Copyright Architype

    Good architects will develop a pallet of ‘tried and tested’ materials

    Through years of experience leading architects will test different products and reuse those which they believe are the most beneficial.

    Simon points to Architype as an example of a company that has refined its pallet of materials over time. So now they’ll only use a limited range of paints, insulations and material systems.

    “They’ve been doing quite a lot of measurement and monitoring to understand how this process is working or not working. They are then informing themselves and their practice and refining their pallet of products as they go along.”

     

    Natureplus products have been thoroughly researched

    When asked if there are any good ways for self-builders to understand if a product is sustainable, Simon suggests checking out an eco label called natureplus.

    Originating from Germany, the idea of a natureplus product is that the product will only be granted a certificate if it’s from a truly abundant source.

    Natureplus has a detailed lifecycle analysis so you can look at the embodied carbon of a product. But also, all the products are third party independently tested in a laboratory for chemicals and off-gassing.

    Simon continues: “The natureplus criteria commission sets very hard standards to reach and in some cases, no products are natureplus certified. The idea of natureplus is that it’s on the top of the triangle. It’s trying to pull the market up and so it represents really only the best products.”

     

    Manufacturing costs of healthy products will come down

    Currently healthy products are more niche and will probably cost more, but if they were produced in greater quantities the economies of scale would kick in and costs would come down.

    Simon says that France has invested heavily in the production of wood fibre insulation. With at least seven or eight new factories opening in the last couple of years, the prices are already coming down.

     

    Careful specification and installation are important steps

    Quite often the ‘right’ product can be put in the wrong place or installed incorrectly.

    This might lead to moisture build up, for example.

     

    Volatile Organic Compounds (VOCs) can perform a function within materials

    Simon explains: “There is a tension between using low VOC products and quality. It’s a tension that I don’t think will ever go away. But there are issues where, for example, some external paints which are low VOCs have been proved to be rubbish and blistered and need repainting within a year or two.”

     

    Ongoing investigation is crucial

    Simon has been looking at formaldehyde recently to try and understand more about what it is, how it occurs and how to specify for low formaldehyde products.

    “Formaldehyde is a ubiquitous gas. It’s all around us. It’s in my breath, it’s in your blood. Low levels of it is absolutely fine and I think we even need it. But high levels of it are a no-no and it’s a known carcinogen.”

    After testing a school where formaldehyde levels were 10 times the World Health Organisation’s recommended levels, Simon explains how difficult it is to isolate the source. “It could well have come from flooring, carpets, furniture – all of these are common sources of formaldehyde. Certainly, if you’re importing particleboard from China, for example, you may find that formaldehyde limits are off the scale.”

    He does go on to say that it’s not too difficult to specify low formaldehyde products if you do the appropriate checks.

     

    Think beyond performance and cost when specifying

    PVC windows have always been a bit of a bugbear for Simon.

    “They are made from fossil fuels and chlorine is used. Chlorine is a highly energy intensive product to make and the process in this country still relies, in certain cases, on mercury filters. There are still a number of companies in the UK that have a licence to off-gas mercury into the environment.”

    So when choosing a product, consider:

    • How it forms
    • Where it comes from
    • What it’s made from
    • Whether it’s really restorative and environmentally friendly

     

    Find out more

    Visit the website of the Alliance for Sustainable Building Products (ASBP)

    Follow the ASBP on Twitter

    Transcript

    Download a transcript of the interview with Simon Corbey 

     

    Please connect with me