Room to breathe in a house of straw

It might look like a fairytale fantasy, but this peculiar dwelling is an impressive experiment in environmentally friendly construction.

The building looks like a turfed marshmallow, a confection that might melt in the sun. There's something almost Disneyish about this small, squishy-looking dwelling in the Perthshire countryside that might suit a 21st-century Hansel and Gretel.

The building looks like a turfed marshmallow, a confection that might melt in the sun. There's something almost Disneyish about this small, squishy-looking dwelling in the Perthshire countryside that might suit a 21st-century Hansel and Gretel.

It's nothing of the kind, of course. Blunt and nubbly as it looks, the 18 square metre building at Dunning is, in fact, a cutting-edge experiment in environmentally friendly construction. The key ingredient: 80 less than tightly packed bales of straw.

Designed by Edinburgh-based Gaia Architects as an office for Raymond and Jean Young, the so-called Straw Bale Experience has taken the "breathing wall" concept to a new, and rather technically naked, level of exposure. Gaia, who tend to design timber framed buildings for use as community and sports centres, responded to this one-off brief with unusual rigour - yet managed to deliver something pleasantly vervy in the process.

Chris Morgan, the project architect, produced a radical solution by, in effect, doing as little as possible: the concept and the details of this building are quite minimal; the practice claims only one interesting new technical wrinkle. The design was developed in-conversation, as it were. "We chatted with the Youngs and we sketched as we were talking," says Morgan. "The whole form of the building was a response to a site that was not very good. We were trying to tie things together."

But loosely. What Morgan was not trying to do was rely on standard solutions. The central idea was to produce an extremely warm, simply-formed structure that could disperse moisture from without and air from within. "We wondered about putting the bales on a concrete slab - but no, that would have been non-breathable. So we set them on raised concrete pads."

There was rather more to it than that. The base of the bale-walls are set on a raised floor platform, and the floor is tied to a grid of nine raw larch poles. These are set into the half-buried concrete pads. The real innovation concerns the base of the bale-walls, which sit on horizontal wood-wool "boards". These act as a moisture sink for the lower course of bales, which can become temporarily waterlogged. This detail was developed in response to news from North American experiments with straw bale structures, which revealed that the use of damp proof courses under the bales - which might seem logical - tended to trap water and cause rotting.

The only other modern elements in the building are the curved glue-laminated wooden roof supports, double glazing and tension wires to lock the structure together. Otherwise, materials were gathered locally and "we basically plastered straight on to the straw," says Morgan. "We used lime plaster - two coats. Before that, there was an element of filling because the bales were fairly soft and we had to re-tie some of them. They should be smooth and firm. You have to have really solid bales."

Two days of filling and spreading produced 20mm thicknesses of plaster on both sides of the walls, painted with five coats of lime wash. Eighteen months after completion, at a fee-including cost of £16,000, the walls remain secure. "The plaster's absolutely fine," says Morgan."And the bales are in mint condition.

"Bits of the walls will get damp at various times of the day," he notes. "This is Scotland, and it depends on the time of the year. But what we were concerned about is that the walls could easily dry out again. That was the way we went about the design. What matters is the bottom of the bales."

And, for the Youngs, warmth. In this respect, the Straw Bale Experience has proved an extraordinary success. The only heating in the building is a small electric fire, never on for more than an hour a day. It's often more than enough to switch on the lights inside to heat the place up. Just another low-cost day at the cosiest of offices, apparently.