One of the first houses to be classed as five-star under the government's controversial policy to require new homes to be "zero-carbon" will be commercially viable, insists Stewart Milne, the housebuilder.

Unveiling its four- bedroomed demonstration house yesterday the Aberdeen-based company said achieving green status added £20,000 to its cost, mainly because of the micro-renewable equipment needed. But it expects this differential to fall after production levels increase.