Extension planning guide
Single Storey Extension Cost UK
How much does a single storey extension cost in the UK? See realistic prices for different sizes, specifications and regions, including hidden costs to watch for.
Typical budget range
£30,000–£120,000+
Main cost drivers
Size, specification, glazing, foundations
Best use
Feasibility before design spend
Extension example
The kind of rear extension result people picture — but the real budget is driven by structure, spec and ground conditions.
Extension guide snapshot
Per-m² figures help, but hidden build costs still matter
Foundations, steelwork, glazing packages and fit-out choices can swing the project far beyond the headline rate.
Remember
A crisp-looking extension budget can still be wrong if it ignores enabling works, drainage and finishing items.
Good next step
Use the extension calculator after reading to compare realistic size and spec combinations.
Single Storey Extension Cost by Size
| Extension Size | Low Spec | Mid Spec | High Spec |
|---|---|---|---|
| 3m × 5m (15 m²) | £27,000 | £36,000 | £48,000 |
| 4m × 6m (24 m²) | £43,200 | £57,600 | £76,800 |
| 5m × 7m (35 m²) | £63,000 | £84,000 | £112,000 |
| 6m × 8m (48 m²) | £86,400 | £115,200 | £153,600 |
Costs assume brick & block construction, builder-grade finishes, and basic kitchen/bathroom fit-out. Excludes architect fees, planning, and structural engineer.
What's Included in the Build Cost
A typical single storey extension build quote includes:
- Strip foundations and concrete fill
- External brick and block walls
- Roof structure and covering (flat or pitched)
- Doors and full-height sliding or bi-fold doors
- Windows (double or triple glazed)
- Insulation to current Building Regulations (SAP 10)
- First-fix electrics, plumbing and heating
- Plastering, drywall and decoration
- Damp proof course and waterproofing
- Waste pipe runs and connections
What Costs Extra
- Kitchen or bathroom fit-out (units, worktops, appliances, sanitaryware) — £5,000–£30,000+
- Underfloor heating — £1,500–£4,000
- Skimming or re-plastering of existing walls adjacent to extension — £500–£2,000
- New boiler or heating upgrades if extension significantly increases heating load — £2,000–£6,000
- Structural steel to open up between existing house and extension — £1,500–£5,000
- Landscaping to step outside — £2,000–£8,000
Does a Single Storey Extension Add Value?
Almost always yes — if done well and appropriate for the property and area. A £50,000 extension that adds £75,000+ to a property's value is a typical outcome in most of the UK.
The key is matching the quality and scale to the property. A mid-spec extension on a mid-value property works well. Over-improving with premium finishes in a modest property rarely makes financial sense.
Calculate your extension cost
Get a more detailed estimate including region, size and specification level.
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