House extension guides
Straight answers to the questions people ask before they extend, written to help you plan and budget.
How much does a house extension cost in 2026?
A typical single-storey rear extension costs about £1,750 to £3,400 per m² including VAT in 2026, so a standard 4 m × 5 m room is around…
Read the guide →Do I need planning permission for an extension?
Many single-storey extensions do not need a planning application because they fall within permitted development. In England that usually…
Read the guide →What is prior approval for a larger home extension?
Prior approval for a larger home extension is an English scheme that lets you build a single-storey rear extension of up to 6 m (8 m for a…
Read the guide →Do I need a lawful development certificate for an extension?
A lawful development certificate is not compulsory, but it is the clearest proof that an extension built under permitted development was…
Read the guide →What building regulations apply to a house extension?
Almost every house extension needs building regulations approval, whether or not it needs planning permission. The regulations cover…
Read the guide →When does the Party Wall Act apply to an extension?
In England and Wales the Party Wall etc. Act 1996 applies when an extension involves work to a shared wall, a new wall on the boundary, or…
Read the guide →How long does a house extension take?
Most single-storey extensions take 10 to 16 weeks on site, and two-storey extensions 16 to 24 weeks. Before that, design and approvals…
Read the guide →Single-storey or double-storey extension: which is better?
A single-storey extension is simpler, quicker and often avoids a planning application, and suits a bigger kitchen or living space. A…
Read the guide →Side return or wraparound extension: which should I choose?
A side return extension fills the narrow passage beside a terraced house and widens the kitchen; a wraparound adds a rear extension as…
Read the guide →Orangery, glass box or solid extension?
A solid extension is the warmest and cheapest per square metre, an orangery adds a large roof lantern and more glazing for light, and a…
Read the guide →Flat roof or pitched roof for an extension?
Flat roofs suit modern designs, give more ceiling height and make roof lanterns easy; modern single-ply, EPDM and GRP systems perform well…
Read the guide →How much glass can an extension have?
In England, the windows, roof windows and doors in an extension should not normally exceed 25% of the extension's floor area plus the area…
Read the guide →Can I build an extension over a drain or sewer?
Often yes, but building over or within 3 m of a public sewer in England or Wales needs the water company's consent, usually through a…
Read the guide →How do I plan a house extension, step by step?
Plan an extension in seven steps: set a budget with a contingency, get a measured survey, agree the design, confirm the planning route…
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