House Extensions: What You Need to Know Before Building

A concise guide to extension types, planning permission, building regulations, typical costs, and how to avoid common pitfalls. ## Extension Types **Single-storey rear** — the most common domestic extension. Typically 3–6 metres deep, adding a kitchen-diner or living space. **Double-storey rear** — adds space on two floors.

More cost-effective per square metre than single-storey but requires more structural consideration. **Side return / infill** — fills the gap beside a terraced or semi-detached property. Popular in Victorian and Edwardian homes. **Wrap-around** — combines rear and side extensions into an L-shape. Maximises ground-floor space.

**Over-garage / above** — adds a first-floor room above an existing single-storey structure. ## Planning Permission Many single-storey rear extensions fall within **permitted development rights** (up to 3m for attached properties, 4m for detached — or 6m/8m under prior approval). You will need full planning permission for: - Extensions exceeding permitted development limits - Properties in conservation areas or AONB - Listed buildings - Extensions facing a highway ## Building Regulations All extensions require Building Regulations approval regardless of planning status.

This covers structure, fire safety, drainage, ventilation, insulation, and electrical work. ## Typical Costs (2026) | Type | Cost per m² | Typical Total | |---|---|---| | Single-storey rear | £1,800–£2,800 | £30,000–£60,000 | | Double-storey rear | £1,400–£2,200 | £50,000–£100,000 | | Side return infill | £2,000–£3,000 | £25,000–£45,000 | | Wrap-around | £1,800–£2,500 | £50,000–£90,000 | These figures include build, foundations, roof, electrics, plumbing, and basic finishes.

Kitchen and bathroom fit-out is additional. ## Common Pitfalls 1. Underestimating groundwork costs (especially on clay soils or sloping sites) 2. Not engaging a structural engineer early enough 3. Overlooking the Party Wall Act requirements for work near boundaries 4. Starting without a clear brief — changes during construction are expensive 5.

Not budgeting a 10–15% contingency --- ### What to do next If you are thinking about a house extension, EvoHome Improvements can help you understand the realistic scope, plan the project sensibly and, where appropriate, connect it with suitable independent installers or specialists. EvoHome does not carry out the works directly.

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