May 7, 2015 / 11:46 AM / 4 years ago

Huffing and puffing won't blow these straw homes down

A batch of straw houses have gone on sale in the UK - and their manufacturers insist that unlike the home featured in classic nursery rhyme The Three Little Pigs, huffing and puffing will not lead the buildings to blow down.

In fact, the architect of the scheme, Professor Pete Walker of the University of Bath, says that using straw in home construction isn’t just viable, but safer than other traditional building materials, and will lead to vastly reduced energy bills for inhabitants.

Seven of the homes have been built in the west country town of Shirehampton, and cost a similar amount to a traditional red-brick house to construct. According to Walker, “you can see that the building is clad in red brick but underneath that are the straw bales which form this super-insulated wall construction, whereas the houses around here are largely brick cavity construction. So the innovation really has laid in developing the suitability of straw as a construction material and also convincing people that straw is a viable construction material. People often refer to the nursery rhyme of the Three Little Pigs, and as a result I think people need convincing that straw is robust, safe, durable, and a modern construction material.”    

Walker says that straw is used in two different ways in the construction. “In this particular building straw has been used in two ways. First of all it’s used as straw bales, so the bales come directly from the farmer from wheat straw, and that is in the outside of the walls, so it’s there as installation behind the brick walls, and then inside compressed straw panels are being used as lining panels and as dividers to separate the rooms as well,” he said.

The 3.2 meter by 2.9 meter ModCell straw panels consist of an engineered timber frame which enclose the compressed straw bale insulation. The load-bearing straw panels are constructed within an airtight design, in conjunction with triple glazed windows. According to Walker, the straw walls provide three times’ greater insulation than required by current UK building regulations, so fuel bills should fall by up to 90 per cent.

The homes were built by Bristol-based company ModCell, in conjunction with Walker’s team at the University of Bath’s Department of Architecture & Civil Engineering. The university department has been developing the technology for around 15 years, initially building a prefabricated straw bale building on campus called the BaleHaus as a test site in 2009.

Walker says using straw has other positive environmental benefits, utilizing some of Britain’s seven million tonnes of straw remains left after the production of wheat flour, around half of which is discarded due to its low value. This leftover straw could be used to build more than 500,000 new homes, as an average three-bedroom house needs 7.2 tonnes of straw. Straw also absorbs carbon dioxide (CO2), rather than releasing it, as happens with brick and cement.

“We’re not displacing food crops to grow, (as) in the case where the materials have been used to grow biofuels,” said Walker. “We already grow wheat because we need it for bread and for other uses, so we’re just using a material that’s already available on the market. And as a plant, through photosynthesis, it actually absorbs carbon dioxide from the atmosphere and that carbon dioxide is effectively stored within the straw. So it comes in the form of a carbon sink, so it’s carbon storage within the fabric of the building and so the more straw you use the more carbon you store within your building for the life of the building.”

ModCell straw panels have also, perhaps counter-intuitively, proved particularly resistant to fire. “They passed the fire resistance requirements more than satisfactorily,” said Walker. “The panels here which are not lined with lime render had a fire resistance of about 52 minutes and they need fire resistance of 30 minutes for use in housing. But one panel that we used, which was rendered with lime, onto the straw actually had a fire resistance of two hours and fifteen minutes before we stopped the test. So in fact it’s remarkably resistant to fire.”

The seven homes were put up for sale by Bristol social housing firm Connolly and Callaghan, at £220,000 (330,000 USD) for two bedroom houses and £235,000 (250,000 USD) for four bedroom ones. The four-bedroom have been oversubscribed. Connolly and Callaghan hope to build a further 49 more straw homes nearby.

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