Single storey extension

Beenie

We are looking to demolish an existing timber framed garden room and replace it with a 5m x 5m tradional brick/render extension. There will be bi-fold doors and a couple of double glazed windows. The roof will be flat.

We know that building costs are around £2000+ per square metre but does anyone know how much we should expect to pay for having the extension supported on piles? The ground is heavy clay, plus we are on a sloping site. We are nervous that the groundwork might cost as much as the actual extension.

System

Why are you removing the timber frame extension? Can it not be adapted?
Piles can be expensive, however in your local area it's likely to be done regularly unless you've got very unfortunate ground conditions! So local builders/architects/engineers etc should know the expected cost uplift locally

Beenie

The existing extension is too small (2.5m x 5m) and has a roof that has started to leak. It also looks like a conservatory/garden room and we want something more in keeping with the house.

All things considered, we have decided not to repair but to demolish and hopefully improve. For one thing, we have a lovely garden which we would enjoy more if we had an extension with bi-fold doors.