What does a side return extension cost in London?
In London: £45,000 to £63,000 for a typical 12 m2 project at mid-range, including 20% VAT, against £36,000 to £50,400 nationally. Budget starts around £38,300, premium runs to £88,200. Set your own size, finish and region below, no email required.
Side return extension, mid-range, London
£45,000 to £63,000
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
- Working in a narrow strip: access and logistics make the per-metre price the highest of all extensions.
- The roof: glazed or part-glazed side return roofs are where the drama and the money sit.
- Drains: the side return often hosts the original drains, which then need moving.
- The party wall: terraced and semi-detached side returns usually trigger party wall agreements.
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. How to pay for it (remortgage, loan or savings) is its own guide: paying for a renovation. Planning an extension or loft? Check permitted development first.
Frequently asked questions
Why is a side return so expensive per square metre?
You are buying a small number of square metres with all the fixed costs of a full extension: foundations, steels, roof, glazing and drain moves in a tight strip with awkward access. The value is in what it does to the whole ground floor, not in the metres themselves.
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 £36,000 to £50,400; 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.