Kitchen Extension Cost in Marylebone: 2026 Price Guide

Ask a local builder what the most common job in Marylebone is, and a rear kitchen extension is usually near the top of the list - understandable given Georgian townhouses, mansion flats and mews houses around Harley Street and the Portman Estate across much of the area. Most homeowners are chasing the same thing: a proper kitchen-diner instead of a cramped galley kitchen.

Typical costs

• Small extension (up to 15m²): roughly £30,000-£45,000
• Medium extension (15-25m²): roughly £45,000-£70,000
• Larger or wraparound extension (25m²+): £70,000 upwards

Treat these as a starting point rather than a quote - they assume standard building work and a reasonable-but-not-luxury fit-out. Adding bifold doors, a roof lantern or underfloor heating will push the final number up.

What affects the price locally

In Marylebone, the biggest local factor is usually access. Many streets are close terraces with no side access, which means materials have to be carried through the house and skips have to sit on the road - both of which builders will price in. Properties within the Harley Street, Portman Estate and East Marylebone conservation areas sometimes face tighter controls on matching brick, roofline and window styles to the existing building, which can add to material costs even for a rear extension that doesn't need planning permission.

Foundations matter too - the Victorian and Edwardian housing near Marylebone High Street and Regent's Park was typically built on shallower footings than current standards expect, so a structural engineer often specifies extra depth that a modern property simply wouldn't need.

Do you need planning permission?

Many single-storey rear extensions fall under permitted development, but there are limits on how far you can extend without full planning permission, and those limits are usually tighter for terraced and semi-detached houses than detached ones. If your home is in one of Marylebone's conservation areas, permitted development rights can be restricted further, so it's worth checking with the City of Westminster's planning department - or a builder who works in the area regularly - before you commit to a design.