In 60 seconds
A house extension is one of the most effective ways to add space to a home, but the process involves more than just finding a builder. Most single-storey rear extensions fall within permitted development rights in England — you may not need a planning application at all, though prior approval is often required for larger extensions. Every extension, however, requires building regulations approval: inspections at key stages and a completion certificate at the end, without which you may struggle to sell the property. Typical costs range from £20,000 for a modest single-storey addition to £100,000+ for a large double-storey project, with London and the South East around 20–40% higher. If your extension is within 3 metres of a neighbour’s building, the Party Wall etc. Act 1996 also applies, requiring written notice before work starts. The right starting point is understanding your planning position and getting at least three written quotes from builders who have seen your drawings.