Two storey extension cost

MyJobQuote, updated in October 2026, gives the clearest breakdown of two storey extension costs by size, with a basic, average and high figure for each. Its sizes are total floor area across both storeys, so a 40m² extension might be a 20m² footprint built on two floors. The page also prices a fitted kitchen and a bathroom as add-ons, which is a useful reminder that the build price and the fitted room are two different things.

On the question of how a two storey extension compares with a single storey one, MyJobQuote says it typically costs 50% to 75% more than a single storey extension of the same size, and MyBuilder says multi storey extensions are 'usually around 50% more'. Which? makes the same point in words, noting that a two storey extension 'isn't simply double the cost of a single-storey structure'. One reason is that the foundations and the roof serve both floors.

MyJobQuote does not say whether these totals include VAT or professional fees, so ask any builder you speak to exactly what their own figure covers.

Knowing how a budget usually splits helps you read a builder's quote and spot anything that looks unusually high or low. MyJobQuote gives a percentage split for a typical two storey project and a cost range for each trade, which shows how much of the job sits with the structural build compared with the finishing trades. It also quotes a builder giving around £850 per square metre for labour only, or £1,550 per square metre with all structural materials included.

MyJobQuote also suggests a buffer of around 10%, and Which? recommends a contingency of around 10 to 15%. Two storey work often uncovers surprises in the existing structure where the new walls tie in, so a contingency is worth keeping aside rather than spending on upgrades at the start.

Two storey extensions are more limited under permitted development than single storey ones, and many will need a householder planning application. The Planning Portal sets out these rules for extensions of more than one storey to houses in England:

• It must not extend beyond the rear wall of the original house by more than three metres.
• It must not be within seven metres of any boundary opposite the rear wall of the house.
• The roof pitch should match the existing house as far as practicable, and upper floor side windows must be obscure glazed.
• All side extensions of more than one storey need householder planning permission.
• Extensions and other buildings cannot cover more than half the land around the 'original house', and cannot be higher than the highest part of the existing roof.

These rights apply to houses only, not flats or maisonettes, and in conservation areas and other designated land every rear extension of more than one storey needs planning permission. Listed buildings need listed building consent for alterations that affect their character. The householder planning fee in England is £548 from 1 April 2026 (GOV.UK), and the Planning Portal adds a service charge of £99 or £149 including VAT, depending on the band, for online applications with a fee over £100. Always check with your local planning authority, read our guide to extension planning permission, and remember that permission is never guaranteed.

Building regulations approval is needed as well, through the council or a private registered building control approver. A full plans application, which suits a two storey project with structural drawings, gets a decision within five weeks, or two months with your consent. The table shows example charges from three West Sussex councils for larger extensions. Adur and Worthing's figures include VAT, Arun's are before 20% VAT, and Mid Sussex's are its charges from April 2025, before VAT. Charges vary by council, so check your own council's building control page.

MyJobQuote says a two storey extension takes up to 14 weeks to build, and gives labour costs and build times by size. These times are for the build only, so add the time needed for design, a planning decision, building control approval and any party wall notice period before work can begin.

When the quotes come in, make sure each builder has priced the same drawings, structural calculations and specification. Ask for itemised prices that show VAT, scaffolding, steelwork, roofing, windows and any provisional sums, and confirm who is responsible for building control inspections and party wall notices. Compare payment stages, the written contract and the builder's insurance as well as the bottom line, since the cheapest figure is often the one that leaves the most out.

To get prices from builders who work locally, fill in our short form or call 01273 115520 for up to 3 free quotes from checked local builders, free and with no obligation. For a first figure you can also use our extension cost calculator.