How much does a single storey rear extension cost in 2026?

Most projects land between £42,000 and £95,000, with the middle of the market around £62,000. The spread is wide because specification moves the number far more than size does. Two identical footprints can differ by thirty thousand pounds on glazing and finishes alone.

How long does a single storey rear extension take?

Allow 12 to 18 weeks on site once work begins. Before that, design and planning typically take eight to sixteen weeks depending on whether you need permission. The build is the predictable part. The approvals are where projects slip.

Do I need planning permission for a single storey rear extension?

Often not. Many of these fall under permitted development, which means no application at all, provided you stay within the size limits and are not in a conservation area or covered by an Article 4 direction. The Project Calculator will tell you which side of the line you are on in about a minute.

What makes the price go up the most?

Three things, in order. Moving drainage or a soil stack. Structural openings that need steel, particularly wide ones. And glazing, where the jump from standard doors to a slim framed sliding system can add fifteen thousand pounds on its own. Size is a surprisingly small factor by comparison.

Is it cheaper to extend or to move?

Extending almost always wins on pure cost. Stamp duty, agent fees, legal costs and removals on a typical UK move comfortably exceed the cost of a well judged extension, and you keep the house, the street and the school catchment. The exception is when the house cannot take what you need.

Cost guide · Updated 2026

How much does a party wall surveyor cost?

Charged per neighbour, and you usually pay for their surveyor too. Serve notice early and a consenting neighbour costs you nothing.

£900£2,500

These are Extnd estimates built from recent UK project costs, not official statistics. Treat them as a planning range rather than a quote.

Axonometric drawing of a single storey rear extension, with the proposed work picked out in green — The wall you share, and the notice it needs

Where the money actually goes

What the fee is made of, and which parts you can avoid.

Item	Typical cost	What it covers
Notice served, neighbour consents in writing	Free	Free. This is the outcome to aim for
Agreed surveyor acting for both sides	£900	One surveyor, one award, lowest paid route
Two surveyors, one each	£1,800	Each side appoints. You pay both
Schedule of condition	£250	Photographs and notes of the neighbouring property before you start
Third surveyor referral	£800	Only if the two appointed surveyors cannot agree
Additional neighbour	£1,500	A mid terrace has two. Both need notice

What moves this number

Drainage. If a soil stack or manhole sits where you want to build, budget several thousand before anything else happens.
Structural openings. Wide steels need bigger foundations at both ends. A five metre opening is not twice the price of a two and a half metre one.
Glazing. The single biggest lever. Standard doors to slim framed sliders can be a fifteen thousand pound swing.
Ground conditions. Clay, trees nearby or a high water table all push foundations deeper.
Where you are. London and the South East run roughly twenty to thirty per cent above the national average on labour.

Project Calculator

Get your cost in 60 seconds.

Every project is different. The Project Calculator prices your actual footprint, spec and region, and tells you whether it needs planning at the same time.

Open the Project Calculator 60 seconds

Questions people ask before they commit

Do I need a party wall surveyor for an extension?

Only if your neighbour dissents or does not reply to the notice within fourteen days. If they consent in writing, no surveyor is needed at all. Most rear extensions on terraces and semis trigger the Act because they build on the boundary or excavate within three metres of the neighbouring foundations.

Who pays for the party wall surveyor?

The person doing the work pays, including for the neighbour's surveyor if they appoint their own. That is why the cheapest route is a consenting neighbour, and the second cheapest is an agreed surveyor acting for both sides.

When should I serve party wall notice?

At the same time as your planning application. Two months notice is required for most works, so serving it early means the party wall clock runs alongside the planning clock instead of after it.

What happens if my neighbour ignores the notice?

Silence counts as dissent after fourteen days. A surveyor is then appointed on their behalf, at your cost. It does not stop the work, it just makes it cost more and take longer.

Compare with other projects

Cost guide

Twenty minutes with the team that sweats the details.

No obligation, no script. An honest read on what your house can do, from people who obsess over getting it approved.

Twenty minutes, by phone or video, whenever suits

Anywhere in the UK, whatever your council

You leave knowing what is possible, and roughly what it costs

How much does a party wall surveyor cost?

Where the money actually goes

What moves this number

Get your cost in 60 seconds.

Questions people ask before they commit

Compare with other projects

Loft conversion

Side return infill extension

Two storey rear or side extension

Wraparound side and rear extension

Basement conversion or dig out

Integral garage conversion

Front porch extension

Twenty minutes with the team that sweats the details.

Book your free call

That is booked in.

What can I help with?