Wrap your building up warm

Construction is no stranger to thin margins, but for really meagre pickings the wool industry takes some beating. Wool simply doesn't have a market any more, as Christine Armstrong knows only too well - she was brought up on a hill farm and her partner has a flock of 1,000 sheep. When looking for a breathable insulation for their 17th century farmhouse in Cumbria, she made two discoveries: (a) that sheep's wool was one possible material but also (b) that it was expensive, mainly because wool insulation products were all imported from abroad.

Five years later, with the help of Leeds University's textile department, Armstrong has created Thermafleece, a BBA-approved insulation made entirely from the fleeces of British hill sheep. The length and consistency of the coarse fibres from hill breeds such as Swaledales and Herdwicks are apparently ideal for the purpose, as well as being cheap. According to her company, Second Nature, Thermafleece is around £3 per sq m cheaper than imported rivals, costing £8.95 per sq m for a 100mm-thick roll.

That's great news for British hill farmers, but is it any good in construction? Nick Dale, architect at Lancashire County Council, specified 1000m² of Thermafleece for the roof of a new block of 10 classrooms at Ribblesdale High School in Clitheroe, Lancashire. He says the unit cost was a little higher but made little difference to the £1m deal. What swung it for him were the health and safety benefits and the relatively local sourcing.

Unlike rockwool and glass fibre products, Thermafleece can be laid in roofs, walls and floors without installers having to don masks and gloves. Dale says there's a big safety push on nationwide, and Thermafleece lets him show the HSE inspectors that Lancashire is doing its bit.

Safe and easy handling is a plus, but the peculiar chemistry of wool make it a perfect insulation material too. Because wool can lose and absorb water vapour readily and rapidly, Thermafleece helps keep buildings cooler in hot weather and hotter in cold weather.

How come? When the outside temperature rises, wool releases moisture, which reduces the flow of heat through the material. Likewise, in colder weather, wool absorbs moisture. Used with a breather membrane to keep out cold air and rain, Thermafleece can keep a building between four and six degrees warmer in the winter and cooler in the summer.

When other open fibre materials such as glass fibre take up humidity, their efficiency soon deteriorates. But wool can take up some 40% of its dry weight in moisture without any effect on its 0.039 U-value. In fact, as wool absorbs moisture it generates heat, which prevents condensation by keeping the temperature in cavities above dew-point in damp conditions.

So will this bring wealth back to the wool industry? Probably not. One fleece provides enough material for around half a square metre of Thermafleece and Second Nature buys around 10,000kg of wool a month - too little to make much headway. But it is a significant tonnage in a long-depressed market. As company spokeswoman Penny Randell says: "We've created an end use for a product which didn't otherwise have one."

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