How long does a house extension take?

Most people underestimate how long an extension takes overall, because the build itself is only part of the story. Here is a realistic picture of each stage, from first idea to moving into your new room. Every project is different, so treat these as typical ranges rather than promises.

The overall picture

• Survey and design: around 2 to 6 weeks.
• Planning: up to 8 weeks for a householder application, or 42 days for prior approval. None if it is permitted development.
• Building Regulations approval: up to 5 weeks for full plans, often running alongside planning.
• Party wall notices: 1 to 2 months notice, usually served in parallel.
• The build: around 8 to 16 weeks for a single-storey extension, 12 to 20 weeks for two storeys.

So a permitted development single-storey extension might take around 4 to 6 months from first contact to completion, while a double-storey extension needing planning is more often 6 to 9 months.

Design and approvals

It starts with a measured survey and design drawings. Once you are happy with the design, we work out whether it is permitted development, prior approval or a full planning application. Councils aim to decide householder applications within 8 weeks. Building Regulations drawings and structural calculations can be prepared at the same time, so the build is ready to start once approval comes through.

Typical build stages

• Site set-up, foundations and drainage: 1 to 2 weeks.
• Walls up to roof level: 2 to 3 weeks.
• Roof, windows and doors (watertight): 1 to 3 weeks, depending on glazing lead times.
• First fix electrics, plumbing and heating: around 1 week.
• Knock-through into the house and steelwork: a few days.
• Plastering and drying: 1 to 2 weeks.
• Second fix, flooring and kitchen fitting: 1 to 3 weeks.
• Decoration, snagging and Building Control sign-off: around 1 week.

What causes delays?

• Long-lead items: bi-fold doors, roof lanterns and kitchens can take several weeks to arrive.
• Ground conditions: unexpected drains, tree roots or soft ground can mean deeper foundations.
• Weather: heavy rain or frost can pause groundworks and brickwork.
• Design changes: changing your mind mid-build costs time as well as money.

How to keep your project on track

Make the big decisions early: glazing, kitchen, flooring and finishes. Order long-lead items as soon as dimensions are confirmed. Serve party wall notices in good time. And choose a builder who gives you a clear programme and keeps you updated.

Planning your extension?

We give every client a clear programme with their quote, and we keep you informed at every stage. See our home extensions or book a free site visit.