A garage conversion costs £10,000–£20,000 for a standard single garage in the UK in 2026, averaging around £14,500. That works out at £625–£1,250 per square metre — the cheapest habitable space you can add to a house. A double garage runs £12,000–£30,000, and a self-contained annexe with bathroom and kitchenette £25,000–£60,000+. Every conversion requires building regulations approval even when planning permission is not needed.
What does a garage conversion cost by room type?
What you turn the garage into drives the budget more than the garage itself does. A home office or gym needs no plumbing and sits at the bottom of the range; anything with a bathroom or kitchenette jumps a full tier because of drainage, Part P electrical work and extra building control stages.
| Conversion type | Typical cost (UK, 2026) |
|---|---|
| Home office / gym / playroom | £8,000 – £15,000 |
| Bedroom / guest suite | £10,000 – £20,000 |
| Utility + boot room (partial conversion) | £6,000 – £12,000 |
| Self-contained annexe (bathroom + kitchenette) | £25,000 – £60,000+ |
How much does a garage conversion cost per m²?
A garage conversion costs £625–£1,250 per square metre in 2026 (Checkatrade), rising to £950–£1,250+/m² for high-spec finishes with underfloor heating and premium glazing. A standard UK single garage is about 16m²; doubles run 28–32m². Per square metre, this beats every alternative: extensions cost £1,800–£3,300/m² and loft conversions £1,000–£2,500/m² — the shell, roof and access already exist, which is why the garage route is so efficient.
Garage conversion cost breakdown: the component line items
This is the table most guide sites leave out and every builder quotes item-by-item. A single-garage conversion budget breaks down like this:
| Component | Typical cost (2026) | Notes |
|---|---|---|
| Insulation + damp-proofing (floor, walls, ceiling) | £1,200 – £2,000 | Part L + Part C — never skip |
| Door in-fill + joinery | £1,300 – £1,800 | Brick in-fill with matching lintel |
| Electrics + lighting | £600 – £1,000 | Part P — registered electrician |
| Plumbing + heating (radiator/spur) | £1,000 – £3,000 | Higher if adding a bathroom |
| Floor screed/raise + levelling | £800 – £1,500 | Garage floors sit below damp course |
| Plastering + skimming | £900 – £1,600 | |
| Building control + inspections | £200 – £500 | Building notice or full plans |
| Fire doors + alarms (integral garages) | £300 – £800 | Part B — mandatory for integral |
Garage Conversion Cost Calculator
Set garage size and spec for a 2026 estimate.
How much does a double garage conversion cost?
A double garage conversion costs £12,000–£30,000 depending on spec and whether it becomes one large room or two. Doubles benefit from economies the single never sees: one door in-fill, one heating circuit, one set of inspections across 30m². houseup's 2026 data puts integral conversions from £9,600 and detached doubles with plumbing significantly higher — detached structures need their own heating solution and a new insulated floor slab.
Do I need permission to convert my garage into a room?
Usually not for planning permission: an internal conversion falls under permitted development provided the building is not enlarged and the space remains part of the main house. You replace the garage door with a matching wall and window, and the rules are satisfied. Exceptions that DO need permission: listed buildings, conservation areas, Article 4 directions, detached garages becoming self-contained annexes, and flats (no permitted development rights).
Building regulations approval is required in every case — planning and building control are separate systems. Apply via a building notice (£200–£500) or a full plans application. The inspection stages: floor (damp + insulation), structural opening, first fix (electrics, insulation depth), fire safety, and completion certificate. Keep the certificate — you will need it when selling or remortgaging.
Which building regulations apply to a garage conversion?
| Regulation | What it requires | Typical cost to satisfy |
|---|---|---|
| Part A — Structure | Lintel over the door in-fill; floor loading for habitable use | In door in-fill budget |
| Part B — Fire safety | Fire doors between integral garage and house; interlinked smoke alarms; protected escape route | £300 – £800 |
| Part C — Damp | Damp-proof membrane to floor and walls | In insulation budget |
| Part L — Insulation | U-values to floor (0.18), walls (0.28), ceiling (0.16) | £1,200 – £2,000 |
| Part F — Ventilation | Trickle vents or mechanical ventilation | £100 – £400 |
| Part P — Electrics | Registered electrician self-certifies | £600 – £1,000 |
One rule trips people up: the converted space must remain part of the main house, not a separate dwelling (Planning Portal). Add a bathroom and kitchenette with independent access and you have built a self-contained annexe — different planning treatment, and mortgage lenders see it differently too.
What is the cheapest way to do a garage conversion?
The cheapest workable single-garage conversion lands at £8,000–£12,000. The savings that don't compromise sign-off: in-fill the door in matching brick rather than specifying glazing; take heating from the existing system with one radiator (not underfloor); keep plumbing out of the design entirely; and DIY the decorating and flooring, which together run £1,500–£3,000 in trade quotes. The savings that DO compromise sign-off and must not be taken: thinning the insulation below Part L, skipping the damp membrane, or using an unregistered electrician — building control will fail the inspection and the certificate never arrives.
Is a garage conversion worth it?
A garage conversion adds roughly 10% to property value while costing £10,000–£20,000 — on a £350,000 house that is ~£35,000 of value for a £14,500 spend, the strongest return of any renovation in the UK. It creates a habitable 15m² room for a third of the per-m² cost of an extension. The exception: inner-city streets where off-street parking is genuinely scarce and every other house has kept its garage — there, the parking space can be worth more to the next buyer than the room is to you. House extensions remain the better route when you need more than 16m².
How long does a garage conversion take?
A standard single-garage conversion takes 2–3 weeks on site, plus 2–4 weeks for building control certification. Annexe conversions with bathrooms run 3–6 weeks. It is the fastest major renovation in the UK: the shell, roof and access exist, there is no scaffold, and the disruption is contained to one room. Sequence: strip out (1-2 days), floor work (3-5 days), in-fill and structural (2-4 days), first fix (2-3 days), insulation and plaster (3-5 days), second fix and finish (3-5 days).
Frequently asked questions
How much does it cost to convert a garage to a room in the UK?
£10,000–£20,000 for a standard single garage (£625–£1,250/m²), averaging ~£14,500. Doubles £12,000–£30,000; annexes £25,000–£60,000+.
Do I need permission to convert my garage into a room?
Usually not for planning — internal conversions are permitted development. Building regulations approval is always required. Listed buildings, conservation areas and self-contained annexes need permission.
What is the cheapest way to do a garage conversion?
£8,000–£12,000: no plumbing, one radiator from the existing system, brick door in-fill, DIY decorating and flooring. Never cut insulation or damp-proofing — building control will fail it.
Is a garage conversion worth it?
Yes — ~10% value uplift for a £10k–£20k spend, the best cost-per-m² of any UK renovation. Only exception: city streets where off-street parking is scarce.
How much does a detached garage conversion cost?
£15,000–£30,000+ — needs its own heating, a new insulated floor slab and a separate fire-safety approach. Self-contained detached annexes (£25k–£60k+) need planning permission.
Do garage conversions need building regulations?
Always. Parts A (structure), B (fire), C (damp), L (insulation), F (ventilation) and P (electrics) all apply. Building control fees: £200–£500.
Does converting a garage devalue your house?
Rarely — done properly it adds ~10%. Risk exists only where parking is scarce locally or the conversion is visibly DIY. Keep the exterior matching and file the completion certificate.
How long does a garage conversion take?
2–3 weeks on site for a single, plus 2–4 weeks certification. Annexe conversions 3–6 weeks. Fastest major renovation in the UK.
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