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Building his hou of straw didn't do the first little pig any favours, but a modern take on straw-bale construction may well be the grand design of the future if results coming out of the University of Bath are accepted by the construction industry.
Think of a straw-bale hou and you might imagine a tumbledown shack that leaks, creaks, slumps and smells somewhat of the farmyard. But step into BaleHaus, a startlingly contemporary looking prototype home that has been built on the Bath campus, and there's nary a wisp of straw to be en. Instead, you're in the hallway of an upside-down hou with two bedrooms and a bathroom on the ground floor, and an airy open-plan living area upstairs. It feels like a little piece of Scandinavia has just arrived in Somert.
The straw bales, it turns out, are all packed tightly inside a ries of prefabricated rectangular wooden wall frames, which are then
lime-rendered, dried and finally slotted together like giant Lego pieces, called ModCell panels.
The problem with straw hous, it ems, isn't that they don't work, but that people perceive them as being a bit hippy and not particularly durable. Add to that the problems of getting a mortgage – very few lenders will consider straw-bale construction –and it's hardly surprising that most homes in the UK are still built of either brick or stone.
The benefits of straw, points out Professor Peter Walker, director of the University of Bath's BRE Centre for Innovative Construction Materials, are that "it's cheap, widely available and a good insulator. It's been ud in building hous for hundreds of years."
As a by-product of an industry that exists all over the world –the stalks that remain after grain has been harvested –straw also helpfully soaks up carbon from the atmosphere and locks it in, so long as it is not allowed to decompo. For the building industry, which currently depends on materials with very high embedded energy costs –concrete and brick are expensive in carbon terms both to make and to transport – straw could therefore offer a welcome solution to housing's greenhou gas emissions.
However stylishly modern your environmentally friendly straw-bale hou may look, howe
ver, you still want to know that it won't get sopping wet in a thunderstorm or go up in a whoosh of flames if you knock over a candle. The results now being published by Walker and his rearch partner, Dr Katharine Beadle, who have spent the last 18 months testing the BaleHaus against an exhaustive list of risk factors that could rot it, burn it or blow it down, so far em to be reassuring.
"You always want a bit of drama, but we didn't get it!" laughs Beadle of the day the team took a ModCell unit to a test laboratory and tried to reduce it to ashes by strapping it to a fiery furnace and raising the temperature to over 1,000C.
"It's a standard test to replicate a fire in a building," explains Walker.
"You want a minimum of 30 minutes' resistance; that means you know that a hou will at least retain its structural integrity for half an hour, which gives people a chance to get out."
It took an hour-and-a-half of being in direct contact with the flames, says Beadle, before t
he lime render began to drop off, "and then the straw did start to burn back, but becau it's so compacted it suffered more charring than actual disintegration."
After waiting another 45 minutes and finding that the panel still hadn't failed, the team gave up and stopped the experiment, cure in the knowledge that the material had performed way beyond the requirements of building regulations.
When it came to blowing the hou down – hydraulic jacks were placed against the walls to replicate wind forces pushing against the bales –the ModCell panels moved a few millimetres, but stayed within the tolerances allowed for by the computer modelling carried out prior to its construction.
That, says Walker, could be very good news for the price of the eventual ModCell building system.
"It means the hou is stiffer than it needs to be, so we now have the option of taking away some of that stiffness – ie, reduce its internal timber – and that could reduce the cost."
The approximate cost of the current modular building system for this de sign is ￡132,000 from above the concrete slab. For a smallish
two-bedroomed hou with one large open-plan kitchen/diner, that doesn't em particularly cheap given that straw is suppod to be inexpensive, and you'd still have to buy the plot and dig the foundations.
"Cost is a challenge to the introduction of this technology, but as a prototype hou I think it stacks up well," says Walker.
"The aspiration is that it should be cost-competitive, with more savings coming through reduced heating bills."
To replicate the heat given off by humans and appliances, arrays of incandescent lightbulbs on timers blaze in every room at pre-programmed times of day "to e how much heat escapes, and what level of heating would be needed at different times of year," explains Beadle.
