Tag: environment

Homes storing CO2, just like trees

Houses built with bio-based materials, such as timber, straw and hemp, act as CO2 banks. Experts explain how citizens can become custodians of atmospheric carbon dioxide and thus help reduce air pollution

Domestic efforts play an important role in curbing global warming. Besides producing and using renewables, homes can also act as banks that store CO2. This innovative building model exploits bio-based materials, such as timber, straw and hemp, which act as “carbon sequestrators.”

Carbon is banked through photosynthesis made by plants during their lifetime. “Photosynthesis is the means with which plants absorb atmospheric CO2 molecules, and split them into their component atoms. The carbon atom is retained making complex organic sugars that are the building blocks of the cellulose, hemi-cellulose and lignin found in plant cell walls. The oxygen atoms are released back into atmosphere as a by-product. Therefore, photosynthesis converts atmospheric CO2 into carbon-based materials that we can use to build and insulate our houses”, says Finlay White, expert in low energy “passive” buildings.

When plants die, the ground absorbs the stored carbon dioxide, which then finds its way back into the environment. However,  if we use bio-based materials in construction, the CO2 remains “imprisoned” in the buildings made.

But how much carbon dioxide can be stored in a carbon sequestration house? White explains that “depending on the extent of the renewable materials used, the gross amount of CO2 equivalent stored could be as much as 55 tonnes for a typical 80m2 house. Such dwellings would typically use timber framing for the superstructure and for the internal walls and floor, straw bale insulation in the roof, timber for the cladding and finishes, and other bio-based materials for use elsewhere.”

“The gross amount is the actual CO2 absorbed by the bio-based materials used in the building. The net amount will need to take account of the energy used and subsequent CO2 emissions associated with dealing with the forests and crops, and turning the materials into useful building products and delivering them to site. This is known as embodied carbon”, he adds.

“Therefore the calculation for a bio-based house will be the gross CO2 captured minus the CO2 emissions embodied in making the house. A typical 80m2 bio-based house with a gross CO2 capture of 55 tonnes might well mean a net amount of 33.6 tonnes.”

White works for the Bristol-based green technology firm Modcell, which contributed to the construction of what they claim to be the world’s first commercially available houses built using straw (more info in this BBC report).

They are also collaborating with the European project Isobio, which is developing “new products that include compressed straw board that can replace plasterboard, cereal fibres combined with bio polymers to make components for door cores etc.”, says White, “Once a designer becomes aware of the use of bio-based materials, the potential for their use expands rapidly.”

Carbon sequestration houses still remain a niche market in Europe.

Callum Hill, senior visiting research fellow at the University of Bath, another Isobio expert in the field, points out that “the building industry tends to be very conservative in its approach and prefers to use what it is familiar with. Bio-derived materials are often perceived as being perishable, flammable and short-lived. These perceptions are not supported by facts”. Compressed straw bales used for building envelopes, for example, are not flammable because they contain less oxygen.

Hill thinks that governments should recognise this alternative storage of atmospheric carbon dioxide and “provide a financial benefit for custodians of it. “It is a way of storing atmospheric carbon dioxide that can be readily achieved and without financial penalty (unlike carbon capture and storage)”, he says, “This is something that can be done to the benefit of society and the environment. Anthropogenic carbon emissions are undoubtedly changing the climate and these will have huge financial implications”.

 

By Luigi Serenelli

17 November 2016

The Social Life of Bricks

A celebrity in the materials world, Mark Miodownik dreams of colour-changing walls and looks at the future of renewable buildings

Mark Miodownik will never forget the day he became obsessed with materials. He was a schoolboy in 1985 when he was stabbed in the London Underground. “When I saw that weapon in the police station later, I was mesmerized. I had seen razors before of course, but now I realized that I didn’t know them at all. (…) its steel edge was still perfect, unaffected by its afternoon’s work,” he writes in his bestselling book Stuff Matters.

Growing up, Miodownik turned his fixation into a successful career. He became a materials scientist at the University College London, the director of the UCL’s Institute of Making and a widely known speaker and BBC presenter. His research interests include biomaterials, innovative manufacturing, and sensoaesthetics, a science that investigates the intricate relationship between people and the materials they use.

We asked Miodownik to share his views about the rediscovery of traditional materials in modern architecture, and how tomorrow’s buildings will cross the border between new and old technologies.

 

Do you think there is still value in using wood, straw, wool, or other traditional materials for buildings?
I don’t see being “traditional” as a value per se. The choice of materials has to be assessed with modern criteria, which include sustainability and energy consumption. If you ask me whether traditional materials are appropriate for modern buildings, I think the answer is yes. Partly because traditional materials have a portfolio of properties that are sometimes better than anything we have created recently: wool, for example, is a fantastic insulator.

Partly because it’s the whole ecosystem that matters. In the old days, the building materials we used were part of the landscape, and they were easier to recycle. New materials are not usually like that. When it comes to sustainability, traditional materials are often more efficient.

 

Construction experts point to limits in the public perception. Some described the three little pigs syndrome, a misconception by which buildings made with traditional materials, such as wood, would not be not as stable or durable as concrete. Is this vision widespread? And does our cultural background influence how we perceive materials?
There is no simple answer. Anthropological studies show that different cultures favour different materials, but the ways people relate to materials is extremely complex. The texture, the feel, the colour or even the imperceptible smell of an object can affect our emotional state. The materials we choose for our house, or the clothes we wear, not only represent us are but they also change how we are. Therefore, the materials we choose for a building can have subtle social consequences.

However, I don’t think that the “three little pigs syndrome” you describe is so widespread. People generally trust the engineers and rarely think about buildings collapsing, unless they live in an earthquake zone.

Rather, I believe that the influence of the global culture is predominant. People worldwide associate concrete, glass, and steel with modernity – think of the iconic image of a skyscraper – and this cuts across many cultures, especially in countries that are switching from rural to urban.

In the industrialised countries, I see much more of the opposite syndrome: many people don’t like concrete and are looking for alternative materials to build their homes.

 

My sports shoes have a new waterproof layer and a classic leather upper. Will buildings go the same way, layering technologies and crossing the border between old and new materials?
Doing this will require more interaction between experts from different industries, and I would like to see more of it. The construction sector is not very diverse in its approach, and I think we have a problem with asylum mentality in general, but real innovators will cross the boundaries between disciplines.

Textiles, for example, are fascinating for architects because they can do things that normal construction materials cannot do. You can see this with the lightweight pneumatic panels that cover many stadiums. Temporary structures are another sector that could benefit from innovative textiles. Millions of refugees need decent housing. Smart constructions made with resistant and lightweight fabric could be quickly sent, packed and reused.

In the future, building materials will be more diverse because people themselves are so diverse with their needs and desires, and constructions will reflect that.

 

You suggested replacing school libraries with workshops where students could get in contact with materials. Does a digital generation really need the physical experience of touching and feeling stuff?
I think the digital world is just one aspect of life. It clearly isn’t the answer to everything. Humans are physical beings; they need food, sleep and shelter from the weather. My radical proposal came after seeing the massive decrease in the facilities for learning with materials. For some schools, digital technology has been an excuse to reduce the resources for physical workshops because they are more expensive.

Whenever we introduce students to physical stuff they love it. And if we combine their digital skills with material knowledge, we can actually empower them. Professionals, too, need to cope with the wealth of new stuff. The number of materials from which designers can choose has almost quadrupled in the last 15 years.

This is why we are now seeing more materials libraries: facilities that collect samples so that designers and engineers can find out how materials could be used.

 

What would be your dream material for a building?
I’ve always fancied buildings that harvest their own energy. On a more immediate scale, I would like constructions to be thermochromic, meaning that they would change their colour with temperature.

Buildings could turn white in summer reflecting more sunlight, and thus reducing the need for cooling. And they could become darker in winter to absorb more heat and thus save energy.

Thermochromic glasses are already on the market. My laboratory developed a thermochromic brick about 10 years ago. We couldn’t get any company interested, but we showed that such a brick was possible.

This material makes total sense from an environmental perspective. As an extra, I would love to be in a city where the buildings change with the seasons.

 

By Sergio Pistoi

21 April 2016