Straw bales may not be everyone's first choice of material for a new home, but it was the natural choice for Jim & Kate Carfrae of Totnes, when they set themselves the challenge of building as sustainable a house as possible for the same £250,000 budget it would take to build a more conventional home.
Jim focused his budget on the overall insulation levels and sustainability of the materials used in the house rather than spending large sums on renewable energy sources. "If the building consumes as little energy as possible, it matters less where the energy comes from," he says.
When told of the plan, their builder, Rob Gulley, roared with laughter. "Rob is from a farming family, so the idea of using straw bales to build a house caused great amusement," explains Jim. "But as soon as he realised we were serious, he found a way to do it."
The main structure of the house is a large section, traditionally jointed timber frame in locally-sourced, sustainable Douglas fir. The walls are made from straw bales, waste material from a local farm, with an inch of fat lime render on each side. Timber for the internal studwork was locally sourced, with a wallboard made from recycled newspaper. The floorboards were recycled from an old chapel. The house has two heating systems, a wood burner for the open plan living area, and conventional radiators in the bedrooms fed by a thermal store heated by a small condensing boiler and a 30 tube solar thermal array. Low-E glass is used throughout, and there is a rainwater harvesting system in the garden.
"The best thing that Rob brought to the project was the way he adapted his undoubted traditional skills to a completely new way of thinking. We'd say what we wanted to do and he'd come up with a practical way to achieve it," said Jim.
Rob suggested using a ladder between the straw bales, both to keep the walls straighter and to provide a fixing point for both the inner and outer walls. In doing so, Rob adapted a traditional technique used by stone masons who used wood with stone to provide fixings. Rob also found a local tannery to supply loose sheep wool, to provide a thermally efficient and cost effective roof insulation material.
The result is an attractive and super insulated home, with a SAP rating of 108, and a Carbon Index of 9.0.
"To go zero-carbon would have cost us much more," said Jim, "But we've noticed a huge difference in warmth compared to conventional homes. There's an even temperature through the house with no cold spots. Our gas bill is £80 per year and that's with no renewables."
