How much does a single-storey extension cost?
Last reviewed July 2026
A single-storey rear or side extension is the most popular way to add space to a home around Cambourne, usually to create an open-plan kitchen-diner. Here’s an honest guide to what affects the cost, and how we price it.
The short answer
The honest answer is that it depends. The size and layout, the kitchen and glazing you choose, and the ground conditions all move the figure, so two extensions of the same footprint can cost very different amounts. Rather than put a number online that we’d then have to caveat, we visit, measure up, and give you a fixed written price for free.
What affects the cost
Every job is different, so we don’t put a figure on this page that we’d then have to caveat. These are the things that move the price up or down. The only accurate number is a measured written quotation, which we give for free.
Size and layout
Floor area is the biggest driver, but so is complexity. A simple square extension is more straightforward than one with lots of corners, roof lights or structural openings into the existing house.
Kitchen and glazing spec
On most extensions, the kitchen and the glazing (bi-fold or sliding doors, roof lanterns) swing the budget more than the brickwork does. A modest spec keeps things down; a designer kitchen and wall-to-wall glass pushes it up.
Ground conditions and access
Foundations can’t be seen in the finished job but they matter. Trees, drains or soft ground mean deeper footings, and tight access that rules out machinery adds labour.
Common questions
- How much does a single-storey extension cost per m²?
- There’s no honest one-size figure, because the rate depends on spec, access and ground conditions. We give you a fixed price for the actual job after a measured visit, rather than a per-m² guess that won’t match your home.
- Is an extension cheaper than moving house?
- Often, yes, once you factor in stamp duty, estate-agent fees and the cost of moving, and you keep your location and school catchment. We’ll give you a fixed quote so you can compare properly.
- Do I need planning permission?
- Many single-storey rear extensions fall under permitted development, but Cambourne’s estate rules can be stricter, so it’s worth checking. We’ll advise at the free site visit.