Garage Conversion Cost in 2026: Single, Double & Integral
Last updated: June 2026 · Figures verified against live North London quotes and current council planning records.
Quick answer: A single garage conversion costs £12,000–£24,000 in 2026 (around £1,440–£1,920 per m²). An integral garage is cheapest at £10,000–£14,000, a double runs £15,000–£30,000, and a detached garage £18,000–£35,000. Plumbing or premium finishes push to the top of each range. VAT at 20% applies.
A garage conversion is the most affordable way to add a proper room to a house — and the reason is simple. The four walls and the roof already exist, so you're not paying for foundations, brickwork or a new roof the way you would with an extension. You're paying to turn a cold store into a warm, dry, legal room. This guide gives the real 2026 cost by garage type, the cost per square metre, exactly what's included and what isn't (the floor and damp upgrade is the bit people miss), how cost changes by what you use the room for, and whether it adds value. We're a North London design-and-build company based in Cockfosters, working to fixed prices with our build partner Pinegrove.
How much does a garage conversion cost?
The single biggest factor is the type of garage you're starting from, because each begins from a different point. An integral garage is already surrounded by heated rooms, so it needs the least work and is the cheapest. A detached garage sits on its own and usually needs heating brought to it and often new drainage, so it's the dearest.
| Garage type | Why it costs what it does | Cost (2026) |
|---|---|---|
| Integral garage | Built into the house — walls already partly heated, services close by | £10,000 – £14,000 |
| Single (attached) garage | One external wall; shares a wall with the house | £12,000 – £24,000 |
| Double garage | Twice the floor area, wider spans, more materials | £15,000 – £30,000 |
| Detached garage | Standalone — needs new heating runs, often new drainage | £18,000 – £35,000 |
For context, the national average for an attached single conversion is around £16,800. London sits at the upper end of every range because labour and trades cost more here. The other three things that move you up: adding plumbing, a premium finish, and a detached structure that needs services run to it.
What's the cost per square metre?
The cleanest way to sanity-check any quote is per square metre. For a standard-spec garage conversion in 2026, expect around £1,440–£1,920 per m².
A typical single garage is 12–18 m² of new internal space. So at standard spec:
- A 12 m² garage works out around £17,000–£23,000.
- A 15 m² garage works out around £21,600–£28,800.
- An 18 m² garage works out around £25,900–£34,500.
These per-m² figures land toward the top of the headline single-garage range because they assume a fuller spec. A simpler conversion — say an integral garage turned into an office with no plumbing — comes in lower. Whatever the size, the per-m² rate moves with finish quality and whether plumbing is involved. Our garage conversions hub explains the design-and-build process behind these numbers.
What's included — and what isn't
This is where a cheap quote and a proper one separate. A garage is built to a lower standard than a house: the floor is usually a bare uninsulated slab with no damp proofing, the walls are often single-skin, and there's no controlled ventilation. Turning it into a room you can legally live in means the price has to include real upgrade work.
A proper conversion includes:
- Floor insulation and damp proofing — frequently raising the floor level. This is the main hidden cost versus what most people expect, and the most common corner cut.
- Wall insulation — bringing external walls up to thermal standard.
- New ventilation and moisture control — so the room stays dry.
- Blocking up the garage door opening and building a new wall, usually with a window.
- Plastering, electrics, heating, flooring and a decorated finish.
- Building regulations sign-off — around £500–£1,200 for the building control side.
Typically excluded (or extra):
- VAT at 20% from a VAT-registered builder — always check whether a quote includes it.
- Plumbing — for an en-suite, utility or kitchenette.
- A Lawful Development Certificate (£274) if you want the conversion formally documented.
- Premium finishes, bespoke joinery and high-end flooring.
A conversion that skips the floor, damp and insulation work will look finished and then go cold and damp within a winter — and it won't pass building control or a future house survey. When you compare two quotes, compare what's in them. The cheaper number is usually cheaper because it leaves the expensive, invisible work out.
How does cost change by what you use the room for?
What you turn the garage into changes the price as much as the garage type does — and it comes down to one thing: plumbing. A dry room (office, bedroom, playroom) is cheaper than a wet one (en-suite, utility, annexe).
| End use | Cost impact | Why |
|---|---|---|
| Home office | Lowest | No plumbing; just insulation, power and light |
| Bedroom | Low | No plumbing; warm floor, heating, window |
| Living room / playroom | Low | No plumbing; finish and heating only |
| Bedroom with en-suite | Higher | Adds drainage, a shower room and tiling |
| Utility room | Higher | Plumbing for washer/dryer, worktop |
| Self-contained annexe | Highest | Kitchenette, shower room, own entrance |
The most-searched conversion in the UK is "convert garage to bedroom," and a plain bedroom or office sits at the lower end of every type's range. Add an en-suite and you're into drainage, a shower tray, tiling and a fan — it's the single change that moves you to the top of the range fastest. We design around what you actually need, so you're not paying for plumbing you'll never use.
Does a garage conversion add value?
In most cases, yes — and the maths is favourable because the cost is so low. You're adding 12–18 m² of habitable space for £10,000–£24,000, where the same space as a brick extension costs two to three times more. An extra bedroom or a proper home office is among the most sought-after improvements a house can have.
But there's one trade-off to weigh honestly: parking. Converting your only off-street space can reduce appeal for some buyers, particularly in areas with controlled parking or no driveway. In much of North London that's a fair price for a warm extra room — but if your garage is the only off-street parking, factor it in. Three points to balance:
- A garage used purely as a damp store adds little; a warm extra bedroom adds real, sellable space.
- Losing the only off-street parking can put off a slice of buyers in parking-tight streets.
- A conversion with no documentation (no building control sign-off, no Lawful Development Certificate) can stall a sale — which is exactly why the regs and the paperwork matter.
Planning and building regs — the cost most people forget
Planning permission is often not needed: most conversions are permitted development because you're working within the existing structure, not enlarging it. But it is needed where PD rights have been removed (many newer estates, Article 4 directions), where the home is listed or in a conservation area, or where the original permission carries a condition requiring the parking to be retained — common on newer developments, so check the original permission. A Lawful Development Certificate costs £274 and is worth having to prove the work was lawful. If a full application is needed, it's a £548 householder application (April 2026) plus a £91.02 portal charge.
Building regulations always apply — that's the non-negotiable one. Budget around £500–£1,200 for the floor insulation, damp proofing, wall insulation, ventilation and sign-off. This is the cost people underestimate, and it's exactly what keeps the room warm, dry and legal.
How to get an accurate figure
Online ranges set expectations; they don't price your garage. The real number depends on the type of garage, its current condition (especially the floor and damp), whether you want plumbing, your finish, and your borough's planning position. We give a free site visit and a fixed, itemised quote across North London — including the planning and building-regs position for your exact address, so there are no mid-build surprises. Price it instantly with our Extension Builder, or book a visit below.
Frequently asked questions
How much does a garage conversion cost in 2026? A single attached garage costs £12,000–£24,000, an integral garage £10,000–£14,000 (the cheapest, as the walls are already heated), a double £15,000–£30,000 and a detached garage £18,000–£35,000. That's roughly £1,440–£1,920 per m². VAT at 20% applies on top from a VAT-registered builder.
Why is an integral garage the cheapest to convert? Because the structure is already there and largely warm — an integral garage is built into the house with heated rooms around it, so it needs the least new insulation, heating and structural work. At £10,000–£14,000 it's the cheapest type, while a detached garage costs most because heating and often drainage have to be run out to it.
What's the hidden cost in a garage conversion? The floor. A garage floor is usually a bare uninsulated slab with no damp proofing, and the upgrade — insulating it, damp-proofing it and often raising the level — is the cost people most often underestimate. Together with wall insulation and ventilation, the building-regs work runs around £500–£1,200 and is exactly what cheap converters skip.
Does converting a garage add value to my house? Usually yes — you're adding 12–18 m² of habitable space for far less than an extension, and an extra bedroom or office is highly sought after. The main trade-off is parking: losing your only off-street space can deter some buyers. Always make sure the work is signed off by building control, as undocumented conversions can stall a sale.
Do I need planning permission for a garage conversion? Often not — most conversions are permitted development. But you'll need it if PD rights have been removed (newer estates, Article 4), the property is listed or in a conservation area, or the original permission requires the parking to be retained. A £274 Lawful Development Certificate is recommended either way; a full application, if needed, is £548 plus a £91.02 portal charge.
Want an exact figure for your garage? Use our Extension Builder to price your conversion in seconds, or see our garage conversions hub for how it works. Book a free site visit for a fixed, itemised quote, or call 020 3051 9430 — The Extension Company, Cockfosters, North London.