How Long Does a House Extension Take?
Understanding realistic timescales helps you plan around disruption and coordinate other decisions like kitchen ordering, temporary accommodation or school schedules. This guide covers every stage from first enquiry to handover.
Typical Build Times by Project Type
Single storey extension: 10-14 weeks. Double storey extension: 14-20 weeks. Kitchen extension: 10-16 weeks. Loft conversion: 6-10 weeks. Garden room: 4-8 weeks. Garage conversion: 4-6 weeks. Full home renovation: 3-6 months. New build house: 9-15 months. These are on-site construction timescales from breaking ground to handover and do not include the design and planning phase that comes before.
The Design and Planning Phase
Before construction starts, you need to complete the design and secure any approvals. An initial consultation and feasibility assessment typically takes 1-2 weeks. Architectural design and drawing preparation takes 3-6 weeks. A planning application (if required) takes 8 weeks for a decision. Building regulations submission takes 2-4 weeks. Structural engineering takes 1-2 weeks. In total, the pre-construction phase takes 6-16 weeks depending on whether planning permission is needed.
What Affects Build Time?
Build time is influenced by project complexity, ground conditions, weather (particularly during groundworks and roof work), specification level, material lead times, and whether structural work is required. Listed buildings and conservation area projects may take longer due to additional approvals. Clay soils common in Worcestershire can slow foundation work. Poor weather between November and March can add 2-4 weeks to groundwork schedules.
The Construction Phase Week by Week
A typical single storey extension follows this rough timeline: Weeks 1-2 — groundworks, foundations and drainage. Weeks 3-4 — brickwork and blockwork walls to plate height. Week 5 — roof structure, felt and tiling. Weeks 6-7 — windows, doors and external finishes. Week 8 — first-fix electrics and plumbing. Week 9 — plastering and screeding. Weeks 10-11 — second-fix electrics, plumbing, kitchen fitting. Weeks 12-14 — decoration, flooring, snagging and handover.
Material Lead Times
Some materials need to be ordered well in advance. Aluminium bi-fold or sliding doors typically have a 6-8 week lead time. Structural steelwork takes 2-4 weeks. Bespoke kitchen units take 6-10 weeks. Engineered oak flooring takes 2-4 weeks. Roof lanterns take 4-6 weeks. Planning these orders early — often during the design phase — avoids delays during construction. Your builder should manage the ordering schedule, but early design decisions help.
Living at Home During the Build
Most families stay in the home during an extension build. The most disruptive period is when the existing house is opened up to connect to the new extension — typically 1-2 weeks towards the end of the build. If the kitchen is being relocated or renovated, plan for 2-4 weeks without a functioning kitchen. Dust protection sheeting, temporary doors and good communication with your builder all help minimise disruption.
What Causes Delays
The most common causes of delays are: late design decisions (changing your mind on the kitchen layout or window positions mid-build), material lead times not planned for, bad weather during foundations or roofing, unexpected ground conditions (rock, contamination or existing services), and poor communication between trades. Choosing a main contractor who manages the whole project — rather than coordinating individual trades yourself — significantly reduces delay risk.
How to Keep Your Project on Track
Finalise all design decisions before starting on site. Order long-lead items (windows, kitchen, steel) during the design phase. Choose a builder with a clear programme of works and regular progress updates. Allow a realistic contingency of 2 weeks in your timeline. Make decisions promptly when asked — delayed client decisions are one of the biggest causes of project overrun.
The Full Project Timeline
From first enquiry to completion, a typical single storey extension takes 6-9 months. A double storey extension takes 8-12 months. A loft conversion takes 4-6 months. A full home renovation takes 9-18 months. These include design, approvals, and construction. Use our AI estimate generator to get a personalised budget, then book a consultation to discuss realistic timescales for your specific project.
Frequently Asked Questions
How long does a single storey extension take?
A single storey extension typically takes 10-14 weeks on site from breaking ground to completion. The full project timeline including design and approvals is 6-9 months.
How long does a loft conversion take?
Most loft conversions take 6-10 weeks on site. The full timeline including design and building regulations is 4-6 months.
Can I speed up my extension build?
The best way to speed up a build is thorough preparation — finalising design decisions, ordering long-lead items early, and ensuring approvals are in place before starting on site.
What is the best time of year to start an extension?
Spring (March-May) is ideal for starting groundworks, as longer days and drier weather help foundations set properly. Starting in autumn means groundworks happen in wetter, colder conditions which can cause delays.
How long does the design phase take before building starts?
The design and approval phase typically takes 6-16 weeks depending on whether planning permission is needed. This includes architectural design, structural engineering and building regulations submission.
What causes the most delays on extension projects?
Late design changes, long material lead times not planned for, bad weather during groundworks, and slow client decisions during the build are the most common causes of delays.