Building a double-height extension costs less per metre squared than a single storey addition
If you need extra space on the first floor as well as the ground, a two-storey extension might be the answer. The lower walls need to be strong enough to support the upper floor, but it doesn’t mean that it will cost twice as much. Double the figure for a single floor and then deduct 20 per cent to get a rough idea of the cost. Again, it’s likely you’ll need planning permission and changes must comply with building regulations.
If you’re having trouble with planning permission, don’t despair. A double-height extension within permitted development might be the answer, as these London homeowners found. When Lambeth planning turned down their client’s plans, Charles Barclay Architects realised that by redesigning they could avoid needing planning permission. Under permitted development, a new extension can exceed 4m in height if it is not within 2m of the boundary. So CBA altered the orientation so that instead of running across the back of the house, it would be at a right angle to the property, away from any of the boundaries. The red cedar-clad, two-storey ‘box’ makes a striking addition to their home.
Words: Justine Roffey and Trish Lorenz