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 do building regulations drawings cost?

The technical set that gets your project signed off and lets a builder price it properly. Separate from planning drawings.

£1,500£4,000

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 drawings a builder can actually price

Where the money actually goes

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

Item	Typical cost	What it covers
Construction drawings	£1,200	Sections, details, specifications a builder can build from
Insulation and thermal design	£300	U values and the compliance calculation
Drainage design	£250	Where the new foul and surface water goes
Fire and escape	£150	Particularly for lofts, where escape routes change
Building control application fee	£500	Paid to the council or an approved inspector
Amendments during the build	£200	Things change on site. The drawings have to follow

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.

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Questions people ask before they commit

Are building regulations drawings the same as planning drawings?

No, and this catches people constantly. Planning drawings show what it looks like. Building regulations drawings show how it is built: structure, insulation, drainage, fire. You need both, and the second set is more detailed.

Can I get permission and skip building regulations?

You can skip planning if the project is permitted development. You can never skip building regulations. Every extension and loft needs sign off, including the ones that need no planning permission at all.

Why does the builder want these before quoting?

Because without them they are guessing. A quote from a sketch is a guess dressed as a number. A quote from a full technical pack is a price, and it is the reason builders who see our drawings quote with fewer surprises.

What happens when I sell without a completion certificate?

The buyer's solicitor asks for it and you do not have it. Indemnity insurance is a patch, not a fix. The certificate proves the work was inspected and passed, and it only exists if the drawings were submitted.

Compare with other projects

Cost guide

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How much do building regulations drawings 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

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