What does a rear extension cost in London?
In London: £60,000 to £90,000 for a typical 20 m2 project for a Single storey version at mid-range, including 20% VAT, against £48,000 to £72,000 nationally. Budget starts around £51,000 (Single storey), premium runs to £126,000 (Single storey). Set your own size, finish and region below, no email required.
- Single storey: £60,000 to £90,000 mid-range
- Double storey (per m2 of floor area, both floors): £60,000 to £85,000 mid-range
Rear extension (Single storey), mid-range, London
£60,000 to £90,000
Including 20% VAT. An indication, not a quote: prices vary per trade and property.
Take it further
Prices include 20% VAT. New builds and some energy-saving works can qualify for 0% or reduced VAT; ask your installer.
Got quotes in already? Check if they are fair. Want to know when the money leaves? See the phase-by-phase plan.
Extensions and loft conversions often fall under permitted development. Check before you budget.
What drives the price
- Size and storeys: per square metre a double storey is slightly cheaper, in total it is not.
- Glazing: bifolds, sliders and rooflights are beautiful, expensive line items.
- The knock-through: opening the back wall needs steels and building control.
- Kitchen inside the extension: most rear extensions are really kitchen projects too.
All figures come from the same validated 2026 price data as the calculator above (sources: Checkatrade, MyJobQuote and comparable national 2026 cost guides, checked August 2026; see how we price), so this page and your estimate can never disagree. Outside London? See the national guide, or compare every region in the regional overview. Planning an extension or loft? Check permitted development first.
Frequently asked questions
Does a rear extension need planning permission?
Often not: single-storey rear extensions within 3 m (attached) or 4 m (detached) usually fall under permitted development in England, with a prior approval route up to 6 or 8 m. Our free planning check walks you through it in six questions.
Do these prices include VAT?
Yes, all ranges include 20% VAT. New builds and some energy-saving works can qualify for 0% or reduced VAT; ask your installer whether your project applies.
Why is London so much more expensive?
Labour is the driver: London trades charge roughly 25% above the national average, and parking, access and waste logistics add friction. Nationally this project runs £48,000 to £72,000; the calculator switches region in one click.
How accurate is this range?
It is a guide range from national 2026 cost guides, adjusted for finish level and region. Real quotes vary per trade, property and specification; treat it as a starting point, budget 10 to 15 percent contingency, and always get at least three itemised quotes.