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Get Free Building Extensions QuotesBefore you get quotes, here is what every homeowner should understand about Building Extensions.
Single-storey rear extensions under certain size limits often fall under permitted development. However, larger extensions, those to the side of a property, and all double-storey extensions typically require full planning permission. Your builder should advise on this before you proceed.
Costs vary enormously depending on the size, specification, and location. A basic single-storey extension typically costs £1,500–£2,500 per square metre. A higher-specification build with underfloor heating, quality glazing, and a premium finish will cost considerably more.
Single-storey extensions are simpler and faster to build, and most fall under permitted development. Double-storey extensions offer more space per pound spent but almost always require planning permission and involve more structural complexity.
A single-storey extension of average size typically takes 8 to 16 weeks from work commencing on site. Double-storey and larger projects take longer. Planning permission, if required, adds several months to the overall timeline before any building work begins.
These are two separate processes that are often confused. Planning permission is about whether an extension is acceptable in terms of its impact on the street scene and neighbours. Building Regulations cover the structural and technical standards of the build itself — foundations, insulation, fire safety, structural calculations, and so on. Both must be satisfied for any extension of substance. Your builder should manage both processes, but it is worth understanding what each involves.
Most extensions use traditional brick and block construction. Timber frame and steel frame alternatives are faster to erect and can be more cost-effective for certain projects. Orangeries and garden room-style extensions use more glazing and are suited to ground-floor kitchen and dining extensions. The structural approach affects cost, insulation performance, and build time, and should be discussed during the quoting process.
A reputable extension builder will manage the project from planning application through to final Building Regulations sign-off. They will use a structural engineer for any load-bearing calculations, coordinate sub-contractors for electrical, plumbing, and plastering, and keep you informed at each stage. Ask for references from recent similar projects, check their public liability insurance, and make sure any contract clearly sets out the payment schedule, timeline, and scope of work.
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