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 July 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.

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.