Cost to Extend a Bungalow in 2026 (UK)
Extending a bungalow costs roughly £2,000–£2,800 per m² in 2026 for a single-storey extension. A typical 20m² rear extension lands around £40,000–£56,000, converting the roof space into bedrooms runs £35,000–£65,000, and adding a full second storey costs £70,000–£130,000+. The big decision is whether to extend out and keep single-level living, or go up for more bedrooms. Here's what each route costs in 2026 and where the money goes.
Cost to extend a bungalow by option — 2026
Standard, finished specification. Source: BestBuilders 2026 quote data · 519 UK towns
Cost to extend a bungalow by option (2026)
| Option | Typical cost (standard finish) | With premium glazing & fit-out |
|---|---|---|
| 15m² rear extension | £30,000–£45,000 | £48,000–£58,000 |
| 20m² rear extension | £40,000–£56,000 | £60,000–£72,000 |
| Loft / dormer conversion | £35,000–£65,000 | £70,000–£85,000 |
| Wraparound (side + rear) | £55,000–£90,000 | £95,000–£115,000 |
| Full second storey (~60m²) | £70,000–£130,000 | £135,000–£175,000 |
Ranges assume a mid-range specification and standard foundations. London and the South-East typically sit 20–30% above these figures; parts of the North and Midlands 5–10% below. A second storey may need foundation strengthening, which can add £5,000–£15,000.
Cost by extension type and region
Bungalows are unusually flexible because they sit on a large footprint with a big, low roof. That opens up four routes, each with a different cost per m² before regional uplift.
| Type | Cost per m² (2026) | Best for |
|---|---|---|
| Single-storey rear or side | £2,000–£2,800 | Extra ground-floor living space with no stairs |
| Loft / dormer (chalet) conversion | £1,500–£2,400 | Using the existing roof for bedrooms — often the best value per m² |
| Full second storey (going up) | £1,900–£2,600 | Roughly doubling the floor area — needs strong foundations |
| Wraparound (side + rear) | £2,200–£3,000 | The biggest single-storey transformation |
Converting the roof space is usually the cheapest per square metre because the roof, and often the foundations, are already there. Regionally, London and the South-East sit at the top of every range; the North-East, Yorkshire and much of the Midlands run 5–10% below the national figure. Use our extension cost calculator or the loft conversion calculator for a size- and region-specific estimate.
Extend out or up? The bungalow question
The choice that defines the budget is whether to extend out at ground level or go up into or above the roof. Extending out keeps the bungalow's biggest asset — single-level living with no stairs, which downsizers and older buyers pay a premium for — and is usually the simpler build. Going up, either by converting the roof or adding a full storey, gains bedrooms without losing garden, but it changes the character of the home to a chalet or a house and can price out the buyers who wanted a true bungalow.
As a rule of thumb: if you need more living space and want to stay put long-term on one level, extend out. If you need bedrooms and the loft has the head height, a dormer loft conversion is usually the best value. A full second storey only pays off where extra bedrooms are genuinely scarce on your street and the numbers stay under the local ceiling price.
Where the money goes
| Element | Share of budget | Notes |
|---|---|---|
| Foundations & structure | 25–35% | A second storey often needs the existing foundations checked or strengthened |
| Roof works | 10–20% | New or altered roof for an extension; dormer construction for a loft |
| Glazing (doors, rooflights) | 15–25% | Bi-folds, sliding doors and rooflights are the biggest single variable |
| Internal fit-out | 20–30% | A new kitchen, bathroom or en-suite pushes the top of the range |
| Fees & regs | 5–12% | Design, structural engineer, Building Control and any planning fees |
What's in the price — and what isn't
A builder's quote for the shell and fit-out usually covers groundworks, structure, roof, plastering, first and second fix, and decoration. What often sits outside the headline figure is where a bungalow budget slips:
| Item | Typical cost (2026) | Included as standard? |
|---|---|---|
| Kitchen units & appliances | +£8,000–£25,000 | Rarely — priced separately |
| Foundation strengthening (for going up) | +£5,000–£15,000 | No — depends on the structural survey |
| Bi-fold or sliding doors (3m) | +£2,500–£5,500 | Often an upgrade line |
| Dormer or rooflights (loft route) | +£2,500–£12,000 | Depends on the conversion type |
| New staircase (going up) | +£2,000–£6,000 | No — needed for any upstairs |
| Architect / technician drawings | £1,200–£3,500 | No — see architect costs |
| Structural survey | +£500–£1,500 | No — essential before adding a storey |
| Skip hire & waste removal | +£400–£1,200 | Usually included — confirm |
Always ask whether the quote is for the shell only or a fully finished room, and whether the kitchen, flooring and decoration are inside or outside the figure. On a going-up project, confirm whether foundation works are included or provisional.
How long it takes
- Weeks −6 to 0 — survey, structural check, drawings, planning check and Building Regs submission.
- Weeks 1–3 — groundworks or foundation strengthening; scaffold up for a going-up project.
- Weeks 4–8 — structure and roof, weathertight.
- Weeks 9–12 — glazing, first fix, insulation, plasterboard, new staircase if going up.
- Weeks 12–18 — plastering, floors, second fix, decoration, snagging and Building Control sign-off.
A single-storey extension is typically 10–16 weeks on site, a loft or dormer conversion 8–12 weeks, and a full second storey 16–26 weeks — the most disruptive option, as the roof comes off for a period.
Planning permission and building regulations
Planning permission. A single-storey rear extension on a bungalow often falls under permitted development — up to 6m deep (8m for a detached bungalow) under the prior-approval Larger Home Extension scheme, within height limits. A loft or roof conversion can be permitted development if it stays within volume limits (40–50m³) and doesn't go beyond the existing roof plane at the front. Adding a full second storey almost always needs full planning permission, because it changes the height and appearance significantly. Confirm before you design — see planning for an extension and planning for a loft extension.
Building regulations. Every route must meet Building Regs for structure, insulation, fire safety, drainage and ventilation. Going up is the most demanding: the existing foundations and walls must be proven capable of carrying the extra load, which is why a structural survey comes first. A Building Control inspector signs off the key stages — keep the completion certificate for when you sell.
Choosing the builder: your checklist
- Ask for two recent bungalow extensions or loft conversions you can visit or phone the owners about — not just general building work.
- Ask to see public liability insurance and check it's current and adequate for the contract value.
- For a going-up project, insist on a structural engineer's report before any price is fixed.
- Check whether they belong to a trade body such as the FMB, and verify membership on the FMB register yourself.
- Get a written stage-payment schedule — never more than 10–15% up front — and a fixed programme.
- Get three itemised quotes on identical drawings so the numbers are genuinely comparable.
Where the budget goes wrong
- Foundations assumed, not checked — on a going-up project, discovering weak foundations after work starts is the single biggest cost shock. Survey first.
- Glazing chosen late — bi-folds and rooflights can add £8,000 to a £40,000 job. Price them at design stage.
- Single-level selling point lost — going up can narrow your future buyer pool. Weigh it before committing.
- Kitchen budget forgotten — the build price rarely includes the kitchen going in it.
- No contingency — hold 10–15% back for what the ground and the old structure reveal.
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