Planning a home extension: what a homeowner needs to know

Most people who commission an extension end up making the same set of decisions in the same order. If you understand what those decisions are before you start, the conversations with your builder, architect and planning officer become much easier.

Start with what the extension is for. A kitchen extension solves a different problem to a bedroom over the garage. A side return that lets you keep the original layout of a Victorian terrace is different to a wrap-around that swallows the whole ground floor. Get the brief on paper before you get quotes.

Second is planning. Some extensions fall under permitted development, some need a full planning application. The size of the extension, the site of the house, the age of the house, and whether you are in a conservation area all matter. Your builder should be able to tell you which route yours takes at the site visit.

Third is the structural approach. A single-storey extension with a large sliding door needs a steel beam, and the beam has to sit somewhere. On a two-storey extension the foundations have to be deeper. On an older house the existing walls have to take the new load. A structural engineer is not optional.

Fourth is heat, light and sound. Modern building regulations set minimum standards for insulation, glazing and ventilation. On an extension you have the chance to significantly exceed those standards, which pays back over the life of the building. Ask your builder what they can offer above minimum.

The remaining four decisions are: how you handle the existing kitchen or bathroom while the work is on, how you control cost when items get chosen (kitchens, flooring, tiling), how the drainage is handled if the extension crosses a manhole, and how you sign off finishing and snagging at the end. We cover all eight at the first site visit.