Glue Laminating at Grand Designs Live

This year CAT has been on bit of a promotional tour – travelling to London, Birmingham and London again to attend exhibitions, study fairs and conferences. Each event gave us the opportunity to talk to people about CAT’s work in the field of sustainability. From this coming Saturday however, CAT will be doing more than just talking.

We’re spending nine days camped out in the miniature village that is Grand Designs Live at the ExCel in London. Each day CAT will be providing demonstrations of glue laminating (or glulam) used to build the beautiful ‘wigloo’ you can see onsite in Wales. Jules, the carpenter who designed the toilet in association with Crafted Space, will be doing two demonstrations each day. As well as this, we have some examples of sustainable building techniques with us and the opportunity for people to ask CAT experts questions about their building woes.

Timber Arc Compost Toilet
The glue laminated compost toilet up at CAT

So what exactly is glue laminating?

It’s a process where several layers of timber are bonded together using a durable, moisture-resistant adhesive. The resulting structure can be used in both straight and curved configurations. The build that Jules undertaking requires curved lathes so he uses a ‘former’ to help hold the layers in place as the glue dries.


So why glue laminating?

Glue laminating has much lower embodied energy than reinforced concrete and steel, although of course it does entail more embodied energy than solid timber. However, the laminating process allows timber to be used for much longer spans, heavier loads, and complex shapes.

Glulam is two-thirds the weight of steel and one sixth the weight of concrete – the embodied energy to produce it is six times less than the same suitable strength of steel. Wood has a greater tensile strength relative to steel – two times on a strength-to-weight basis – and has a greater compressive resistance strength than concrete. The high strength and stiffness of laminated timbers enable glulam beams and arches to span large distances without intermediate columns, allowing more design flexibility than with traditional timber construction.

Glue Laminating
Jules clamping some glue laminated timber onto the former

We’ll be following the build live each day over on Facebook so have a look and see how it progresses!

If you like the look of the compost toilet, take a look at Jules’ website.

Grand Designs Live is open to the public from Saturday 4th to Sunday 12th May. More information can be found on their website.


The top 5 renewable energy questions from the National Homebuilding and Renovating Show

If you went to the National Homebuilding and Renovating Show a week ago, you might have been inspired by the live demonstrations of thatching, or felt the sudden urge to redecorate when you passed the stall full of sheepskin rugs. Or perhaps you realised you really did need a 2-metre 3D TV in your lounge, or maybe you simply wanted to browse whilst enjoying an ice cream from the Yorkshire Dales food cart (it’s a permanent installation).

Nestled between two full-size timber frame houses, one of which was the Eco Home Theatre, the CAT stall was a small hub of renewable energy debate in this varied crowd. Enthused by Tobi’s daily talks, a stream of visitors made their way to us to ask often highly specific or technical questions. Some of the same concerns kept coming up, so we’ve collated a list of the five most common questions and Tobi’s answers.

Lots of people also asked us questions about architecture and design, but we’re going to save those for a later feature. Stay tuned!

  1. What’s PVT, and is it a good idea?
  2. Is there a case for thermodynamic systems?
  3. Are heat pumps right for me?
  4. Micro hydro: yes or no?
  5. Should I heat my house with biomass?


1. What’s PVT, and is it a good idea?

PVT is the combination of solar photovoltaic systems (the “PV”), which produce electricity, and solar thermal systems (the “T”, also known as solar water heating, SWH), which produce hot water.

In principle, you can see the potential for synergy between these technologies. PV modules convert only 10%-20% of the solar energy that falls onto them into electricity, and a good proportion of the remaining solar energy is converted into heat – solar PV get hot in the sun. So why not use this heat to heat water for showers? This is what PVT modules do – basically, they are solar PV modules put onto a solar thermal absorber. In principle, this is a brilliant idea. In practice, it’s not so easy.

Solar PV modules actually operate more efficiently when they are colder (because their electric resistance is lower) whereas for your showers you want your water to be hot. Under some conditions that works out perfectly – as long as your hot water cylinder is cold, the solar thermal part will actually cool your solar PV module down. But on a sunny summer’s day you ultimately want your solar thermal system to produce very hot water, and in fact UK legislation actually requires water to be heated to temperatures of 60-70C to kill dangerous Legionella bacteria. Ideally you’d want your solar panel to be colder than that.

You can get around this by using a heat pump to produce very hot shower water while pumping lower temperature water through your solar PVT panels. But that of course means additional expense – and much higher electricity consumption than the circulation pump of a normal solar thermal system. Also, it is worth pointing out that most PVT systems on the market today actually cost more than the combined cost of a conventional PV system and some solar thermal panels.

The Upshot: If you have enough roof space you’re probably better off installing separate solar PV and solar thermal systems.

2. Is there a case for thermodynamic systems? So-called “thermodynamic” systems (a fancy term that doesn’t really mean much) are essentially simple (unglazed) solar thermal panels connected to a heat pump. They haven’t been on the market for long enough for us to have good data, but there’s reason to be very sceptical. In the UK there simply isn’t much solar energy available in winter because days are short and the sun is low down and very often hidden behind clouds altogether.

Under those conditions, a “thermodynamic” system is essentially an air-source heat pump (ASHP) that relies on heat transfer from the ambient air to the solar panel. Manufacturers claim that the system will provide hot water at every time of the year – and that is probably true, but during dark winter days this energy is not solar energy but rather energy produced by a heat pump, which consumes a lot of electricity.

Furthermore, because the “thermodynamic” panels usually use a type of solar panel that’s less efficient than a normal (glazed) solar thermal panel, they’re probably also not a good choice during the sunnier parts of the year when a normal solar thermal system can produce hot water at a much lower electricity cost.

The Upshot: A large dose of scepticism is currently warranted when it comes to these systems. This is also reflected by the fact that their accreditation under the Microgeneration Certification Scheme (MCS) has been suspended, which means you won’t get Renewable Heat Incentive (RHI) income.

3. Are heat pumps right for me? The answer is “it depends”. Heat pumps use electricity to extract ambient heat (heat in the air or ground) and supply that heat into your house. Today most electricity is produced very inefficiently – for instance, our coal and gas power stations consume two or three units of fossil fuel heat energy for every unit of electricity they produce. If electricity from these inefficient power stations is used to run heat pumps, then these heat pumps need to be very efficient. Basically, your heat pump would need to supply three units of heat for every unit of electricity it consumed, otherwise you might be better off heating directly with oil or gas!

To work efficiently, heat pumps need to run at a relatively constant rate supplying heat at low temperatures. This is a realistic option for a (usually new-built) house that is well insulated and has underfloor heating with densely spaced pipes. In this case even when it is very cold outside the water in the heating system need only be lukewarm (maybe 30-35C). On the other hand, if the heat pump needs to supply much hotter water, for a badly insulated building or a building heated by radiators, then the efficiency of the heat pump will likely be too low to make it a good choice.

4. Micro hydro: yes or no? Hydropower is great, and if it benefits a whole community rather than one individual then all the better! Unfortunately, only a minority of communities in the UK have the kind of site that’s suitable for hydropower: A stream with a large flow rate of water and a good height drop. If you have a site of this type then it’s definitely worth exploring the option of installing a micro-hydro scheme.

5. Should I heat my house with biomass? Biomass can be a good choice, especially where wood can be sourced locally and/or for buildings where heat pumps would not work at high efficiency. But it’s important to stress that wood fuel is a limited resource and that there are potentially negative side effects to burning it (e.g. local air pollution from smoke, time lag between when CO2 is emitted and when a new growing tree absorbs it again). This doesn’t mean we shouldn’t burn wood, but it means we should try to use it as efficiently as possible. This means always reducing a building’s energy consumption first, and using the most efficient appliances available for burning wood. For example, modern log batch boilers (wood gasification boilers) get more heat out of the same amount of wood, and emit less smoke, than traditional wood stoves (or, even worse, open fires!).

Have a question about renewables and your home that we didn’t answer here? Check out our Home Energy Handbook, or give our Free Information Service a call!


Photo: Building the new green roof display

Thanks to a generous grant by People’s Postcode Trust, CAT has been able to build a new green roof for the visitor centre. This photo gallery shows the steps that CAT’s Buildings and Maintenance Officer, Carwyn Jones, has used in the building process…

1. The old food-store is one of the oldest buildings at CAT. But it was in dire need of a new roof, so Alex and Carwyn got rid of the old one first. They managed to re-use the membrane though.

2. A frame was built for the new roof. The original timber was reused where possible but as you can see, we needed a lot of new wood. The new timber was sourced from local forestry.

3. Here you can see how Carwyn re-used the old membrane. He also installed a new skylight to increase the light levels in the food-store.

4. This special membrane has pockets in it that collect water to allow for slower drainage. Bigger grades of stone were used on the edge of the roof to border the frame.

5. Almost finished! A layer of slate chippings went onto the roof (notice the extra batons that Carwyn put in place to stop the slate sliding down the roof). Soon the roof will be planted with sedums, which will need less soil and be easier to maintain than turf.

Watch this space for more photos of the new roof. Why not come and see it for yourself over Easter? CAT has a full schedule of Easter activities over the holidays!

Sustainable Architecture Blog: Ramming home the benefits of earth buildings

Building with earth is an incredibly ancient construction method but that doesn’t stop it from being fantastic for modern building design. Rammed earth has excellent construction properties being flexible in design and application. It also embodies low-tech building methods.

Rammed earth is formed from loose subsoil, which is moist and compacted in layers. This presses the material to about half it’s original depth and forces the clay in the earth to bond with the aggregate. Because this process is physical, no chemicals are needed. You do however, need a high enough clay content (around 15-30%).

Due to it’s simplicity, this ancient building technique has been popular all across the globe. Cob, adobe and rammed earth were all used historically and these traditional building methods are now being re-discovered by sustainable developers and architects.

Rammed earth, in particular, is becoming ever more prevalent in modern architecture with the growing popularity for sustainable buildings.

There are many environmental advantages to earth buildings. In most instances, construction with earth requires low energy outputs and emits virtually no pollution. This means that rammed earth has very low embodied energy. The embodied energy of brick is six times that of rammed earth!

The thick walls of compressed earth buildings are also extremely fire-resistant; there are no flammable components and everything is so tightly packed there is little chance of combustion. At the other end of the scale, the addition of a stabiliser makes rammed earth resistant to most moisture but continued exposure to water at the top and bottom of earth walls must be prevented.

Earth has benefits for heating as well. It is a dense material that provides high levels of thermal mass, especially when compressed. However, the thermal resistance of rammed earth is very poor so it’s use in external walls is limited.

Rammed Earth: Design and construction guidelines suggests that “to meet thermal performance levels expected of modern energy efficient buildings… external rammed earth walls must either be very thick (over 70cm) or use additional insulation.”

Rowland Keable, co-writer of the book, began building earth structures nearly thirty years ago and now teaches on many natural building courses. He has extensive experience of working with earth, having published Rammed Earth Structures: A Code of Practice. He also established Ram Cast CIC and is a founder member of Ebuk. Clients of Keable’s have included the Eden Project, Big Brother and Bath University.

Building with earth is a great method for construction, especially when other buildings materials are limited. The Whole House Book states that “earth is the most immediate and locally available material it is possible to build with. It is also one of the cheapest and lowest impact construction methods.

Building with Earth is a three day short course at CAT that gives a thorough grounding in the building method. Designed for anyone that is interested in natural building methods, Keable’s course is very hands on and participants can expect to get muddy!

Podcast: what policies do we need to encourage eco-renovation?

Energy use has been in the news recently, from Ofgem’s warning that Britain will come “dangerously” close to power shortages within two years, to the public outrage in response to Centrica reported that British Gas profits increased 11% after a hike in prices a few months ago.

Following on from our most recent sustainable architecture post, this week’s podcast describes current refurbishment policies in the UK, in particular the Green Deal. Tina Fawcett, Senior Researcher at the Environmental Change Institute at the University of Oxford, explains why we need policy if we’re going to refurbish Britain’s buildings – and what new policies might be effective and feasible.


Previous podcasts

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Sustainable Architecture Blog: The green, green grass on our homes

Green roofs are growing in popularity within architecture and the building industry. They are great for the environment in a number of ways and installing one on your home can make financial sense as well!

These living roofs increase biodiversity, providing vegetation in areas that could benefit from plant species. These plants in turn attract insects and birds. Large green roofs can also act as carbon sinks that absorb CO2 and produce oxygen. The UK’s biggest green roof is in Birmingham.

Another great advantage of the soil in a green roof is that it can absorb rainwater, which slows the run-off from a downpour. This helps reduce the chance of localised flooding in built-up areas. Many more demonstrable benefits can be found here.

However, for a vegetated roof to be environmentally beneficial then the installation has to take into account the materials used. A green roof needs many layers and a strong structure below to support it, all of which could add up to a large amount of embodied energy.

But there are also great financial benefits to a green roof. If properly installed, a green roof can increase the energy efficiency of a building. The thermal mass of a soil roof makes it really effective at insulating the building below. So heating usage decreases by retrofitting a roof to be a green one. Flat un-vegetated roofs can be 20ºc hotter than living roofs!

Cities make ideal surroundings for green roofs. Vegetated roofs can provide fantastic gardens in urban areas where space is limited. There is strong evidence that these natural surroundings improve health and well-being.

Did you know, all new roofs in Copenhagen that are less than 30° steep must be a green roof? This planning obligation was introduced in 2010 as part of Copenhagen’s push to be carbon neutral. Whilst Copenhagen is a much smaller city than London or Manchester, this sustainable initiative could be perfect for improving Britain’s urban districts.

But what if your sustainable design or retrofit can not support a green roof?

Well, green concrete could soon be a feasible construction material for sustainable architects. Biological concrete has been developed by the Structural Technology Group, which could create ‘living’ buildings. The concrete supports the growth of organisms that can help to reduce CO2 levels in the atmosphere.

All of this goes to show that, while turf roofs have been around for hundreds of years, there is life in the old dog yet!

Sustainable Architecture Blog: Should we retrofit or rebuild Britain’s housing stock?


Reassessing our built environment is vital in the fight against climate change as about 45% of CO2 emissions in the UK come from energy used in our homes and buildings. It is vital that the government looks seriously at how Britain can reduce these emissions. But should we retrofit or rebuild Britain’s housing stock?

There are a host of pros and cons to both approaches, and neither is cheap in the short-term. Like most sustainable technologies, reducing the greenhouse gas emissions of a building is a long-term investment. However, the built environment accounts for over 40% of global carbon emissions so it is imperative that reducing this becomes a focus of the international agenda. With climate change looming and energy prices rising, our built environment risks being our greatest liability.


As sustainable building methods become more advanced and efficient, new housing will increasingly impact less on the environment. This is why advocates of rebuilding Britain’s housing argue it is better than retrofitting as a long-term approach to reducing housing sector emissions. On the whole it is much easier to build a passivhaus from scratch than adapt existing housing. Indeed, the cost of refurbishing and maintaining existing homes can often exceed the home’s value.

Sustainable re-building requires low embodied energy and excellent insulation. A new structure that is well insulated with low embodied energy can have a negligible carbon footprint. The environmental impact of demolishing an existing building, especially one that contains little or no wood, can be severely reduced by disposing of the materials responsibly.

However, if large amounts of wood are burnt or allowed to rot carbon is released into the atmosphere (whereas, the carbon in wood can theoretically be locked up in landfill). Architects could incorporate reclaimed timber in their designs to offset these emissions, or even re-use the materials from the original building. The carbon in wood can be stored if it is well maintained.

This technique of locking up carbon within buildings is known as carbon sequestration. This can also be achieved by using buildings materials such as hemp, other biomass and reclaimed building elements.

‘Jobs, Growth and Warmer Homes’, a report by Consumer Focus in 2012, looked at how the UK government should re-invest money raised through carbon taxes and energy efficiency. Responding to these findings, The Energy Revolution argued that the UK government must invest the money by re-building houses. The fuel poverty alliance, the biggest of its type, commented that:

This report shows that in its bid to boost UK economy, the Government is not investing in the one thing which could create more jobs and growth than anything else – re-building the UK’s housing stock. Not only does this have massive economic benefits but it is the most effective way to bring down energy bills.”


Rebuilding the housing sector might not be high on the government’s priorities (although targets have been set to make all new builds from 2016 carbon neutral), but eco-refurbishment certainly is. One of the UK government’s main strategies to reduce greenhouse gas emissions is to make homes more energy efficient. Their flagship policy to tackle home energy efficiency is called the Green Deal. Launched in January, this is a financial investment to make buildings more energy efficient, and is also designed to reduce fuel poverty.

Retrofitting involves the addition of new technologies and materials for the benefit of the property. For instance, improving insulation makes a building more energy efficient and therefore more sustainable. Energy efficient retrofitting is also a rapidly growing market because of the savings that can be made, and it is a much cheaper strategy in the short-term than demolishing and rebuilding properties.

But what should be Britain’s approach to be?

The UK has a tougher choice then developing nations because more of the built environment in newer countries is still to be constructed. This means developing economies can set the tone for sustainable development in a way that the UK cannot. British architects must also consider the cultural worth of historic buildings that already exist. Georgian townhouses may look impressive and have a great sense of heritage, but they can also have woefully inadequate insulation, ineffective heating and aging plumbing.

The Zero Carbon Britain (ZCB) project, a scenario for a carbon neutral United Kingdom by rapid decarbonisation, supports retrofitting the majority of the British housing stock. The researchers propose using natural materials where possible to eco-renovate buildings. Hemp shiv would be an ideal substitute for artificial insulation because it is proven to be resistant to moisture ingress. The hemp used in this insulation could also act as a carbon sink.

But this model is not possible for every home. Writing for the Guardian, Tony Hutchinson argues that:

Looking at the total cost of a refurbishment project over its lifetime (including maintenance and eventual replacement) in both cash and carbon terms the outcome can be very different. Cost and benefit modelling should be used to compare the benefits of demolition and new build with the costs of maintenance of the retrofitted building over its useful life – and the cost of further refurbishment after 30 years or complete replacement.”

So if we are hoping to build truly sustainable communities for the future, developers must look at the long-term. Where possible, Britain should rebuild its housing stock. This will take time, however, and may not be possible by ZCB’s target date of 2030.

Modern architects must be bold during this transition. Many of Britain’s houses will be too expensive to eco-renovate. If historic buildings such as Victorian and Edwardian terraces must be protected, then why not keep the facade but demolish the living spaces behind? A sustainable structure constructed in its place can be integrated with the historic face of the building. Projects like Kings Cross10 Hills Place and others demonstrate that this is achievable. Obviously there will be instances where this is not possible, but architects and eco-builders must think outside the box to find creative ways to decarbonise Britain’s buildings.

Why Sustainable Architecture is the Future

Sustainable architecture holds the key to an environmentally positive future. Only by living more economically with our resources can we hope to protect our environment and climate. So what better way to live more sustainably than by making sure the very structure of our built environment is greener?

The philosophy behind sustainable architecture is all about reducing waste. This not only means physical waste but minimising energy loss as well. By keeping the energy we consume within our buildings for as long as possible, we need less supply in the first place. Using less energy to keep us comfortable means that we can become environmentally responsible and more resource efficient, which are both vital to reducing the effects of climate change.

Governments around the globe are looking at initiatives to make new builds and retrofits more sustainable. The Green Deal was launched in the UK on the 28th of January. This policy is a government initiative designed to persuade businesses and homes to retro-fit green technologies in their buildings. There are also initiatives such as the Passivhaus standard, which sets clear requirements for certificated buildings. As the name suggests, this approach to low energy housing originated in Germany during the early nineties. To meet the standard, a ‘Passivhaus’ must meet an energy demand target. A number of these sustainable assessment methods for architecture exist including BREEAM and LEED.

But while a building might be incredibly energy efficient, the structure’s building materials could still have a huge impact on the climate.

In his book, How Bad are Bananas, Mike Berners-Lee calculates that building a new two bed cottage produces the equivalent of 80 tonnes of carbon equivalent emissions. The majority of this impact is in the walls and the materials used. Much of these emissions can be recouped by using energy efficiency methods while the house is occupied. Yet, if sustainable building practices can reduce the impact of the construction in the first place then this is preferable if we are to become more environmentally conscious.

Construction materials such as rammed earth and building techniques like turf roofs are proven to have less impact whilst holding their own when compared to established but unsustainable methods.

So there are three overriding concerns when designing buildings with better considerations towards ecological impact. The first is the materials used for construction. The second concern is the energy efficiency of the building and the last factor to consider is the location of the building itself. The building might be energy efficient and use low impact construction technologies but this would not mean anything if the ecosystem suffers as a result of the building.

A greater holistic approach to all of these design factors is becoming more prevalent in mainstream architecture.

By looking at what builders have done in the past, forgotten construction techniques that might not be as redundant as previous generations thought, as well as cutting-edge technologies we can inform a brighter future. Our built environments will have less impact on the natural surroundings. This truly is a growing industry and the future of architecture.

Christmas presents that make a difference


If you like me have not even started Christmas shopping yet, you could either put your head in your hands and despair about our consumerist society or do what I did last year and give someone a present that can really make their year. Just before last Christmas, my Dad came up to CAT and was amazed by the wooden pole lathes and shave horses he saw as we walked around CAT. I suggested he might like to do a course; “that would be brilliant!” he said. A few months later he came to visit again armed with his notebook, pencil and a lot of enthusiasm to take part in the Greenwood Crafts course. He had an amazing time,  learnt loads and now has his very own shave horse in the garden shed.  My only problem is this year all my family want a course at CAT for Christmas.

Which is why it’s great that CAT is offering a 10% discount up until 31st December. So if you or a loved one have ever wanted to learn how to build a coracle, make forged tools, or construct gates and fences, give horse logging a go for a day, or spend an intensive week learning the art of sustainable woodland management from experienced woodspeople, now is your chance! I myself have enrolled on the Blacksmithing course and can’t wait, here’s hoping it’s the start of a brand new career.

CAT’s short courses are a great gift idea for anyone interested in learning skills in sustainable living; this festive season, why not give someone you love the opportunity to delve further into an interest, or to take a week out from the hectic pace of life in the tranquility of mid Wales?

Participants on CAT’s short courses enjoy delicious vegetarian meals and accommodation nestled in the foothills of Snowdonia, as well as expert tuition from well-renowned tutors and CAT staff.

Below are some of the fantastic courses on offer in 2013. Book before the 31st and make the most of the 10% discount now available!

Develop your skills in woodland management and crafts

Gates, Fences and Hedges: learn how to create gates, fences and hedges. Ideal for smallholders.
Horse logging: experience a low impact method for logging woodland
Sustainable woodland management: a fantastic introduction to all aspects of managing a small wood. Learn how to add social, economic and ecological value to woodland.
Greenwood crafts: discover the basic principles of transforming greenwood into products.

Reclaim traditional skills

Coracle building: build a traditional vessel used since the Bronze Age in a weekend
Hedgerow herbalism: discover how to produce an incredible range of cosmetic and medicinal products from foraged materials
Willow basket making: spend a hands-on day learning how to weave with willow
Blacksmithing: learn how to use a low-tech, low-fuel charcoal forge and leave with the items you’ve made

Learn sustainable building skills

Strawbale building: learn this sustainable, simple and accessible building method
Make an earth oven: gain the skills to build an earth oven yourself, and secure a future supply of delicious pizza, breads and stews!