Thinking about extending your home in Bromley or the surrounding BR postcodes? Whether you want an open-plan kitchen diner, a double-storey rear extension for extra bedrooms, or a clever side return to bring light into a Victorian terrace, understanding realistic costs in 2025 is essential before you start.
This guide is written for Bromley homeowners — from Beckenham and Chislehurst to Orpington, Eltham and Greenwich — who want clear pricing, planning advice and reliable local insight. It’s based on current market rates and the practical experience of Buildaway, a trusted South East London construction company known for transparent quoting and an 18-month labour warranty.
How Much Does a House Extension Cost in Bromley (2025)?
Prices in Bromley are mid-to-upper London market — not the cheapest in the UK, but competitive compared with inner London. Expect to see these build-only and turnkey averages:
Single-Storey Rear Extension
- Build-only: £2,200 – £2,800 per m²
- Fully finished with kitchen: £2,800 – £3,500 per m²
- Example: a 25 m² kitchen-diner = £55,000 – £70,000 build-only or £70,000 – £90,000 turnkey
Double-Storey Rear Extension
- Build-only: £2,000 – £2,600 per m²
- Fully finished: £2,600 – £3,300 per m²
- Example: 40 m² over two floors = £80,000 – £110,000 build-only or £105,000 – £130,000 turnkey
Side Return & Wrap-Around Extensions
Usually in line with single-storey costs: £2,200 – £2,900 per m² depending on structure and roof glazing.
These are fair mid-market Bromley rates — realistic for quality builders who are fully insured, meet Building Control standards and deliver reliable aftercare.
What Drives the Price Up or Down
- Size & footprint – more square metres means more foundation, roof, insulation and labour.
- Structural steel (RSJs) – removing load-bearing walls adds £2k–£6k+.
- Foundations & drainage – poor ground or moving drains increases costs.
- Roof style & glazing – flat roofs with skylights are cheaper; big sliders/bifolds add £3k–£8k+.
- Kitchens & bathrooms – kitchens typically £10k–£25k+, bathrooms £6k–£15k+.
- Heating & plumbing – consider upgrading to a Megaflo/unvented cylinder if adding bathrooms (£2.5k–£4.5k).
- Finishes & joinery – flooring, decorating, bespoke carpentry all add up.
- Site access & parking – narrow side paths or no parking can increase labour and skip costs.
Planning Permission & Building Control in Bromley
- Many single-storey rear and side return extensions qualify as Permitted Development if within size limits.
- You’ll need full planning if extending more than 3 m on a semi or 4 m on a detached (double-storey always needs permission).
- Conservation areas and Article 4 restrictions (common in parts of Chislehurst, Beckenham & Bromley Town) remove Permitted Development rights.
- Building Control sign-off is always required for structure, insulation, drainage and electrics.
A good contractor can guide you or work with an architect to prepare drawings, structural calculations and planning submissions.
How Long Will It Take?
- Design & planning: 4–12 weeks (longer if full planning)
- Technical drawings & approvals: 2–6 weeks
- On-site build:
- Single-storey: 10–14 weeks
- Double-storey: 14–20 weeks
- Add extra time for bespoke glazing, kitchens or landscaping.
Typical Full Project Budget Breakdown (30 m² Double-Storey)
| Element | Typical Cost |
|---|---|
| Core structure & shell | £70,000 – £85,000 |
| Windows / doors / glazing | £5,000 – £10,000 |
| Kitchen supply & fit | £12,000 – £25,000 |
| Bathroom fit-out | £6,000 – £12,000 |
| Heating / boiler / Megaflo | £3,000 – £5,000 |
| Flooring & decorating | £5,000 – £15,000 |
| Professional fees & permissions | £3,000 – £8,000 |
| Total realistic range: | £100,000 – £135,000 |
(Larger or more bespoke finishes can push beyond £150k).
Why Bromley Clients Choose Buildaway
- Proven local expertise — we know Bromley housing stock, planning quirks and typical construction challenges.
- Transparent quoting — clear staged payments (no hidden extras).
- 18-month labour warranty — longer than most mid-market builders.
- Fully insured & compliant — public liability, employers’ liability, Gas Safe & NICEIC trades.
- Project management you can trust — we handle timelines, neighbours’ concerns, and Building Control.
Frequently Asked Questions
Do I need planning permission for my Bromley extension?
Often not for single-storey if within PD limits — but double-storey, front or side extensions and homes in conservation areas almost always need it.
Can I live at home while building?
Usually yes, especially for single-storey rears. Expect some disruption; temporary kitchen setups help.
Will I need to upgrade my boiler or hot water system?
If adding bathrooms or large kitchens, an unvented cylinder (Megaflo) or new boiler is often wise.
What guarantees do you offer?
Buildaway provides an 18-month labour warranty on all structural and fit-out work for peace of mind.
Next Steps for Bromley Homeowners
If you’re ready to explore an extension:
- Book a free home visit to assess feasibility and budget.
- We can arrange design & planning packages if you don’t yet have drawings.
- You’ll receive a transparent, itemised quote so you know where every pound goes.
📞 020 8108 0388
📧 info@buildaway.co.uk
Buildaway — trusted by Bromley homeowners for bathrooms, kitchens and full extensions done right.