Is £30k enough for a house extension in 2026?
|The honest answer from a Berkshire builder who prices these jobs every week.
It's the question I get asked more than almost any other. You've seen £30,000 mentioned on a forum or a comparison site, your neighbour says that's what they paid a few years back, and now you're wondering if it's still realistic in 2026.
Short answer: it's tight, but possible — for a smaller, straightforward single-storey extension with a sensible spec. For anything larger, two-storey, or with a high-end fit-out, you'll need to increase your budget or reduce your scope.
What does £30k actually get you in Berkshire in 2026?
Build costs in the South East have continued to rise. In 2025/2026, a realistic figure for a single-storey rear extension in Berkshire is between £2,000 and £2,800 per square metre, depending on spec, access, and groundwork conditions.
At those rates, a compact 12m² extension — a small garden room or utility — sits around £24,000 to £34,000 for the build alone. A more comfortable 15m² extension, like a modest kitchen diner, comes in at £30,000 to £42,000. So £30k is still a relevant number, but it's the floor, not the ceiling.
These figures cover structure, roofing, glazing, electrics, plumbing and plastering. They do not include kitchen or bathroom fitting, flooring, decorating or furniture — budget those separately.
What's not included in the build cost?
This is where a lot of homeowners get caught out. On top of the build you'll typically need to budget for:
Architect drawings and planning application fees (£2,000 – £5,000)
Structural engineer calculations (£600 – £1,800)
Building regulations inspections and sign-off
Kitchen or bathroom fit-out if it forms part of the extension
Flooring, decoration and finishing
Groundworks surprises — drains, tree roots, poor load-bearing soil
A realistic all-in budget for a well-finished 15m² extension in Berkshire in 2026 is closer to £38,000 to £50,000 once everything is accounted for.
Does £30k work for a double-storey extension?
No. A double-storey extension adds significant structural complexity, additional roofing, staircase works, and more. Even a modest two-storey addition in Berkshire will start at around £60,000 to £85,000 in 2026. If that's what you're planning, the budget needs a serious rethink before you approach any builder.
Why have extension costs gone up?
Materials costs rose sharply through 2022 and 2023 and haven't come back down to where they were before. Labour costs in the South East have also increased, and lead times on glazing and structural steel remain longer than they once were. Any builder quoting you 2021 prices in 2026 either hasn't priced a job recently or isn't being straight with you.
How to make £30k go further
There are smart ways to keep costs within budget without cutting corners on build quality:
Keep the footprint compact — every extra square metre adds cost directly
Avoid relocating drains or utilities wherever possible
Use a flat or lean-to roof rather than pitched where planning allows
Choose standard rather than bespoke glazing units
Get the shell watertight first, then phase the internal fit-out
Be honest with your builder about budget from the start — it helps everyone
Planning permission and building regs in Berkshire
Many single-storey rear extensions in Berkshire still fall under permitted development, meaning no full planning application is needed. However, building regulations approval is always required — skipping it creates problems when you sell. Properties in conservation areas, including parts of Windsor, Sonning and the Kennet Valley, face stricter rules and will need a planning application regardless of size.
Always confirm with your local authority before assuming permitted development applies to your plot.
The bottom line
£30,000 is still a workable starting budget for a smaller single-storey extension in Berkshire in 2026, but it's tighter than it was two or three years ago. Go in with realistic expectations, get proper drawings done before anyone prices anything, and work with a builder who gives you a detailed fixed quote rather than a number pulled from thin air.
We've delivered extensions across Reading, Wokingham, Windsor, Bracknell and Maidenhead at a range of budgets. If you want an honest conversation about what's achievable on your plot for your money, get in touch and we'll come out for a look.