Home addition / extension cost in London

Indicative market range for London, clearly labelled while our UK planning-data pipeline is in development.

Typical low · P25£55,000
Median£85,000
Typical high · P75£140,000

Indicative market range — UK planning-data pipeline in development

Data refreshed September 2026

The short answer: a typical home addition / extension in London costs around £85,000, with half of all projects landing between £55,000 and £140,000. If a quote falls well outside that range, it isn't automatically wrong — but it deserves an explanation you can understand.

How to use this home addition / extension range

The middle half of the published sample spans £55,000 to £140,000. That is a 100% spread around the median, so the details of your scope matter more than the label on the project.

What this project can cover

An addition or extension can include foundations, structure, roof tie-in, envelope, services, and interior finishes for the new space.

What may sit outside it

Land purchase, temporary accommodation, major utility upgrades, furnishings, and redesign after approval are commonly outside the filing value.

Use your quote to test the range

  • Compare floor area, foundation type, and finish schedule.
  • Confirm planning, structural design, and inspection responsibilities.
  • Price utility connections and site drainage separately.

This guide is an indicative market benchmark, not a sample of permit filings. Use it as an early planning range and replace it with local quotes as your scope becomes clear.

Before you spend on a home addition / extension

💸 What drives the cost

  • Foundations and roof tie-in are the expensive ends; the middle (walls) is comparatively cheap
  • Wet rooms in the new space (kitchen/bathroom) add plumbing runs and cost far more per square metre
  • Planning/zoning constraints can dictate design more than budget does

✂️ How to spend less

  • Build up or convert existing volume (loft, garage) before building out — foundations are the money pit
  • Match, don't fight, the existing roofline to simplify the structural tie-in

🚩 Red flags when hiring

  • A builder happy to start before planning permission/permits are granted
  • No structural engineer involved in a design that touches the existing structure

Home addition / extension in other cities

Other projects in London

Where this number comes from

UK planning and building-control records rarely include cost valuations, so this range is indicative market guidance — assembled from industry benchmarks, clearly labelled, and never presented as filing-derived. Our UK data pipeline is in development. Full methodology →

Questions people ask

How much does a home addition / extension cost in London?

Our indicative market range for London puts the median around £85,000, with typical projects falling between £55,000 and £140,000. This is market guidance, not filing-derived data, and is labelled as such.

Are these figures quotes?

No. These are indicative market ranges, not contractor quotes. Treat the range as planning guidance and a sanity-check against the quotes you receive.

Why is the range so wide?

Because identical-sounding projects legitimately differ in size, specification and site conditions. That is why we publish the 25th percentile, median and 75th percentile instead of a single misleading "average" — you can see where a quote sits in the real distribution.

Planning something else, or somewhere else? Request a city or project — requests decide what we ingest next.