House Extensions Birmingham 2026: Costs, Planning Permission & What to Expect
Written by Tom Ellis · Senior Trades Editor
Last updated: July 2026
Quick Answer
How much does a house extension cost in Birmingham in 2026? Single storey from £25,000, double storey from £45,000. Birmingham-specific pricing, planning permission guide and what to expect.
Last updated: July 2026 · Birmingham, West Midlands
House Extension Costs in Birmingham 2026
House extension costs in Birmingham are typically 10–15% lower than London prices but have risen significantly over the past two years. Material costs, labour shortages and energy price inflation have pushed average build costs up 8–12% since 2024.
The table below shows typical costs for Birmingham extensions in 2026 — these are supply and fit prices including labour, materials, foundations, structural work and basic finishes (plastered walls, basic electrics). They exclude kitchen fitting, bathroom tiling, flooring and decoration.
| Extension Type | Size | Birmingham Cost 2026 | Cost per m² |
|---|---|---|---|
| Single storey rear (basic) | 16m² (4×4m) | £25,000–£35,000 | £1,560–£2,190 |
| Single storey rear (mid-spec) | 16m² | £35,000–£45,000 | £2,190–£2,810 |
| Single storey rear (high-spec) | 16m² | £45,000–£60,000 | £2,810–£3,750 |
| Double storey rear extension | 32m² | £45,000–£75,000 | £1,410–£2,340 |
| Side return extension | 10–20m² | £20,000–£40,000 | £1,500–£2,500 |
| Wraparound (rear + side) | 25–45m² | £50,000–£90,000 | £1,800–£2,500 |
| Over-garage extension | 20–30m² | £30,000–£55,000 | £1,500–£2,200 |
| Basement conversion | 20–40m² | £60,000–£120,000 | £2,500–£4,000+ |
What Affects the Cost of a Birmingham House Extension?
- Size and footprint — the largest single cost driver. Adding 1m² adds roughly £1,500–£2,500 in Birmingham.
- Specification level — standard brick and block, or structural glazing, steel beams and aluminium bifold doors? High-spec glazing alone can add £8,000–£20,000.
- Ground conditions — older Birmingham housing stock, particularly in areas like Handsworth, Erdington and Kings Heath, often sits on clay subsoil requiring deeper strip or raft foundations. Budget an extra £3,000–£8,000 if ground surveys indicate poor bearing capacity.
- Party wall agreements — required if your extension is within 3m of a neighbour's foundations. A party wall surveyor in Birmingham typically costs £700–£1,500 per surveyor (you pay both sides).
- Existing construction — knocking through to join the extension to the house requires structural steelwork. A single RSJ (steel beam) in Birmingham typically costs £1,200–£2,500 installed.
- Conservation areas — parts of Bournville, Moseley, Harborne and Edgbaston fall within conservation areas. Permitted Development Rights do not apply; full planning is required and materials must match the existing building.
Planning Permission in Birmingham
Birmingham City Council follows the national Permitted Development framework, which allows many single storey rear extensions without full planning permission — subject to size limits:
- Detached house: max 4m depth at rear without prior approval; up to 8m under the Neighbour Consultation Scheme
- Semi-detached or terraced: max 3m depth without prior approval; up to 6m under the Neighbour Consultation Scheme
- Maximum height 4m; cannot be higher than the existing eaves height
- Must not cover more than 50% of the original garden area
Prior approval (Neighbour Consultation Scheme): For extensions between 4–8m (detached) or 3–6m (semi/terraced), you must notify Birmingham City Council. Neighbours have 21 days to raise objections. If no objections, the extension can proceed.
Full planning permission is always required for: double storey extensions; side extensions on corner plots; any extension in a conservation area or on a listed building; and properties where PD rights have been removed (check your title deeds).
Full planning application fee: £258 in England (2026). Decision time: 8 weeks for householder applications. A planning consultant in Birmingham typically charges £600–£1,500 if you need assistance.
How Long Does a House Extension Take in Birmingham?
| Stage | Duration | Notes |
|---|---|---|
| Architect / drawings | 2–4 weeks | Required for building regs and planning |
| Planning permission (if needed) | 8–10 weeks | Neighbour consultation: 3–4 weeks |
| Building regulations approval | 2–4 weeks | Can run concurrent with planning |
| Builder lead time | 4–8 weeks | Birmingham builders are in high demand |
| Groundworks and foundations | 1–2 weeks | Longer if difficult ground conditions |
| Structural frame and roof | 2–4 weeks | — |
| First fix (electrics, plumbing) | 1–2 weeks | — |
| Insulation and plasterboard | 1–2 weeks | — |
| Plastering and second fix | 2–3 weeks | — |
| Decoration and finishing | 1–2 weeks | Owner often handles decoration |
Total from first meeting to moving in: typically 6–12 months including planning. Pure build time for a single storey extension is 8–14 weeks once work starts.
Finding a Builder in Birmingham
Birmingham has no shortage of builders, but quality varies significantly. Demand for extension work remains high across all parts of the city, particularly in Solihull, Sutton Coldfield, Harborne and Moseley.
- Get 3 quotes minimum. Quotes for identical extensions in Birmingham regularly vary by 20–40%. The cheapest is rarely best value.
- Check credentials. Look for FMB (Federation of Master Builders) membership, Trustmark accreditation, or membership of the National Federation of Builders. These require vetted references and insurance checks.
- Verify insurance. Any builder working on your property should carry public liability insurance of at least £2 million. Ask to see their certificate — a reputable builder will have it readily available.
- Stage payments. Never pay all upfront. A reasonable payment schedule for a £35,000 extension might be: 10% on contract signing, 30% at foundations complete, 30% at roof/watertight, 25% at first fix, 5% retention on snagging completion.
- Check recent local work. Ask for addresses of recent Birmingham projects and visit them. Talk to the homeowners if possible.
Frequently Asked Questions
How much does a single storey extension cost in Birmingham?
A single storey rear extension in Birmingham typically costs £25,000–£45,000 for a 16m² footprint (4m × 4m) in 2026, depending on specification. High-spec glazing and bifold doors push this toward £45,000–£60,000.
Do I need planning permission for a house extension in Birmingham?
Many single storey extensions proceed under Permitted Development Rights without full planning — provided they stay within depth limits (4m detached, 3m semi/terraced at rear) and height limits (4m). Double storey extensions, extensions in conservation areas, and extensions on listed buildings always require full planning permission from Birmingham City Council.
How long does a house extension take to build in Birmingham?
Build time for a single storey extension is typically 8–14 weeks once work starts. Add 4–10 weeks for planning permission if required, plus 2–4 weeks building regulations approval and builder lead time. Total project duration is often 6–9 months from first architect meeting to completion.
What is the average cost of a double storey extension in Birmingham?
A double storey rear extension in Birmingham costs approximately £45,000–£75,000 for a typical family home. The second storey adds roughly 50–70% to a single storey build cost, making double storey extensions the best value per square metre.
Should I use a local Birmingham builder or a national firm?
Local Birmingham builders typically offer better value and local knowledge than national firms. Look for FMB members or Trustmark-accredited builders. Always get 3 quotes and check recent local references.
Related Birmingham Guides
Get an Instant Extension Cost Estimate
Describe your extension to our AI and get an itemised cost estimate for Birmingham in seconds — free, no signup required.
Get a Free Estimate