House Extensions: What You Need to Know Before Building

A concise guide to extension types, planning permission, building regulations, what affects cost, and how to avoid common pitfalls. You can come to EvoHome at any stage: before planning, after receiving drawings or quotes, when advice conflicts, or once work has started. If you speak to us before committing to surveys or work, we may be able to help you understand what is actually needed first and avoid unnecessary cost or the wrong route.

Tell us what you want to change and what has happened so far; we can help clarify the scope, identify relevant approvals or specialist input, and coordinate suitable next steps. Keep decisions, variations and completion evidence together. ## Extension Types **Single-storey rear** — a widely used form of extension, often creating a kitchen-diner or living space.

The right depth depends on the property, the garden and what is permitted. **Double-storey rear** — adds space on two floors. Whether it offers better value than a single-storey extension depends on the property and scope, and it usually involves more structural and planning 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 Some house extensions may fall within **permitted development rights**, but the conditions depend on the building, site, dimensions and local restrictions.

Check the particular proposal with the local planning authority. You may need a planning application for: - Extensions exceeding permitted development limits - Extensions facing a highway - Listed buildings (which also need listed building consent) In conservation areas, National Landscapes and other designated land, permitted development rights are more restricted, but this does not automatically mean every extension needs full planning permission.

Restrictions differ, so check what applies to your property and proposal with your local planning authority. ## Building Regulations Most house extensions require Building Regulations approval separately from any planning decision; confirm the requirements for the proposed work with building control. This covers structure, fire safety, drainage, ventilation, insulation, and electrical work.

## Costs Extension costs depend on scope and specification, from modest single-room additions to extensive renovations that include kitchens and interiors. The most reliable figure is a property-specific quotation. See the [extension cost guide](/blog/extensions-costs-2026) for what affects the price. ## 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…