How Long Does a Home Extension Take? A Phase-by-Phase Timeline for Homeowners

A single-storey extension takes between 6 and 9 months from start to finish. The build itself is only part of that. Design, planning, building regulations and party wall agreements all add time before a single brick is laid. Understanding each phase helps you plan your life around the project rather than the other way round.

What Are the Main Phases of an Extension Project?

Every extension goes through the same sequence: design, planning permission or permitted development confirmation, building regulations, party wall agreements where needed, and then construction. Each phase has its own timeline and most of them run before anything physical happens on site.

How Long Does the Design Phase Take?

For a straightforward single-storey extension, allow 2 to 4 weeks for architectural drawings and a measured survey of your property. More complex projects with unusual site conditions or bespoke design requirements take longer. Getting this stage right reduces the chance of the council requesting changes later, which costs more time than the drawings ever did.

How Long Does Planning Permission Take?

Councils have a legal target of 8 weeks to decide a householder planning application. In practice, many applications take longer than this due to the volume of applications councils are processing. Allow 10 to 13 weeks as a realistic working figure.

If your project qualifies as permitted development, this stage is removed entirely. A permitted development application can be confirmed in around 6 to 8 weeks, and some projects need no formal application at all.

How Long Do Building Regulations Drawings Take?

Building regulations drawings cover structural calculations, insulation, drainage and construction methods. Once submitted, building control has 5 weeks to respond to a full plans application. The key point is that experienced builders run this in parallel with the planning wait rather than waiting for planning approval before starting. Running these concurrently saves 4 to 6 weeks on the overall programme.

Do I Need a Party Wall Agreement and How Long Does It Take?

If your extension is on or near a shared boundary, or involves work to a party wall, you must serve notice on your neighbours under the Party Wall etc. Act 1996. The notice period for most extension work is 2 months before work can begin.

If your neighbour consents in writing, you can proceed once the notice period expires. If they dissent or do not respond within 14 days, a party wall surveyor must be appointed. From notice to signed party wall award with cooperative neighbours, allow 8 to 12 weeks. Disputes take longer.

This catches many homeowners off guard. Party wall notices need to go out early, ideally while planning is being processed, not after approval is received.

How Long Does the Construction Phase Take?

This depends on the type and complexity of the extension.

A single-storey rear or side extension takes 10 to 16 weeks on site according to multiple UK builders including Resi and JW Building Services. The build follows a set sequence: groundworks and foundations, walls to damp proof course level, drainage, superstructure and roof, first fix electrics and plumbing, plastering, second fix, then decoration and fitting out.

A double-storey extension takes 14 to 20 weeks for construction alone. A wraparound extension takes 16 to 24 weeks or more depending on scale.

One factor that regularly extends construction timelines is bespoke glazing. Large sliding or bifolding doors and roof lanterns commonly carry lead times of 10 to 12 weeks. These need to be ordered before groundworks start, not after the roof is on.

What Is the Realistic Total Timeline for a Single-Storey Extension?

From initial design to completion, a single-storey extension with planning permission typically takes 7 to 12 months. A permitted development project with no planning application can come in closer to 6 to 8 months if design and party wall notices are handled promptly.

The projects that run to the shorter end of these ranges are the ones where decisions are made quickly, bespoke materials are ordered early, and party wall notices go out as soon as the design is confirmed rather than at the last possible moment.

What Causes Delays on Extension Projects?

Planning applications are the most common source of delay and largely outside your control. Council processing times vary and conditions attached to an approval can require revised drawings before work can start.

Bespoke materials with long lead times are the next most common cause. Weather affects groundworks and roofing, particularly between November and March. Design changes once construction has started cascade through trades and materials, adding weeks to the programme.

Frequently Asked Questions

How long does a single-storey extension take from start to finish?

Between 6 and 9 months for most projects, including design, planning and construction. Projects requiring planning permission sit toward the longer end. Permitted development projects can be completed closer to 6 months.

Can building regulations and planning run at the same time?

Yes. Experienced builders submit building regulations drawings while the planning application is being considered. This saves 4 to 6 weeks compared to running them one after the other.

When should I serve a party wall notice?

As soon as your design is confirmed. The notice period is 2 months, so the earlier it goes out the less it delays your start on site. Waiting until planning is approved before serving notice adds 2 months to the overall programme unnecessarily.

What is the most common cause of construction delays on extensions?

Planning applications taking longer than the 8-week target and bespoke glazing lead times are the two most common causes. Ordering glazing and specialist materials as soon as planning is approved reduces the risk of the build stalling while waiting for deliveries.

Does a double-storey extension take twice as long as a single-storey?

Not quite, but significantly longer. Construction alone takes 14 to 20 weeks compared to 10 to 16 weeks for a single-storey extension. The total project timeline including design and planning typically runs to 9 to 15 months.

Use Your Space manages extensions from initial design through building regulations, planning and construction across Solihull, Warwick, Knowle, Dorridge, Bentley Heath, Shirley, Balsall Common, Leamington Spa and Kenilworth. We give you a realistic programme at the outset and manage every phase so nothing falls through the gaps.

Contact Use Your Space today to discuss your project and get a timeline specific to your property.