Most homeowners come to us with a figure from a neighbour’s job three years ago. Materials and labour have both moved since, so here is where prices actually sit.
The headline number
A straightforward single-storey rear extension runs between £2,200 and £2,800 per square metre for a good standard of finish. The spread comes down to three things: groundworks, glazing, and how much of the existing house has to be re-worked to suit the new layout.
Groundworks are the biggest unknown before we start. Old drains, a high water table or a neighbouring tree can all add a week and a few thousand pounds, and none of them are visible from the garden.
What people forget to budget for
Structural calculations, building control fees, and making good the garden afterwards. None are large on their own, but together they are usually about five per cent of the job.
The other one is the kitchen. An extension that opens onto a kitchen almost always means a new kitchen, and that sits outside the building quote.
Getting a number you can rely on
Any builder can give you a rate per square metre over the phone. It will be wrong, because they have not seen your ground, your access or your existing structure. A proper quote takes a site visit and about a week.