Garage Conversion London 2026: Costs, Planning & Complete Guide
A garage conversion is the most cost-effective way to add habitable space in London. The structure already exists. Here are the real 2026 costs, what planning actually requires, and which uses give the best return.
Quick Answer
Garage conversions cost £18k–£70k inc VAT in London. Basic home office £18k–£30k, bedroom £22k–£35k, bedroom with en-suite £32k–£50k, full annex £40k–£70k. Most conversions are permitted development. All need building regulations approval.
£18k–£30k
Basic room
£32k–£50k
With en-suite
£1,100–£2,500
Cost per m²
Check your specific property constraints
Free Property CheckTypes of Garage in London
The type of garage you have determines the complexity and cost of the conversion. There are three main types:
Integral garage
Built into the main body of the house, with living space above. The most common type in London semi-detached and detached houses. Already has roof, walls, and floor. Cheapest to convert because the envelope is fully weathertight and the floor slab already exists.
Conversion cost: £18,000–£40,000 inc VAT depending on spec and use
Attached garage
Attached to the side of the house but with no habitable room directly above. Has its own roof (usually lower than the main house). Slightly more work than integral as the roof may need upgrading and there is no existing floor above to consider structurally.
Conversion cost: £20,000–£45,000 inc VAT depending on spec and use
Detached garage
A separate building in the garden. Can be converted to a home office, studio, or annex. Requires new service connections (electrics, possibly plumbing and heating). May need planning permission if the use changes to a self-contained residential unit. Less common in inner London but frequent in outer suburbs.
Conversion cost: £22,000–£65,000 inc VAT depending on spec, services, and use
2026 Costs by Use
All figures below include VAT at 20%. What you are creating drives the cost far more than the size. A garage converted to a home office is far cheaper than the same space converted to an annex with a bathroom and kitchenette.
| Use | Cost range | Key additions |
|---|---|---|
| Home office / studio | £18k–£30k | Insulation, flooring, electrics, heating, new window |
| Bedroom / playroom | £22k–£35k | Above + fire safety, ventilation, higher-spec finish |
| Bedroom with en-suite | £32k–£50k | Above + drainage, waterproofing, tiling, sanitary ware |
| Home gym | £18k–£28k | Robust flooring, enhanced ventilation, electrics, lighting |
| Utility / boot room | £15k–£25k | Drainage, plumbing connections, practical tiling |
| Annex (bed + bath + kitchenette) | £40k–£70k | Full habitable unit: bathroom, kitchen, separate services |
Cost per m² in London 2026
A typical single garage is 15–20m². A double garage is 28–40m².
These are 2–3x cheaper per m² than a new extension because the structure already exists. No foundations, no new roof, no external walls to build.
Where the cost goes
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Planning Permission: Do You Need It?
Most garage conversions in London do not require planning permission. Changing the use of a garage to habitable space within the same dwelling falls under permitted development (Class C), provided no external alterations significantly change the building's appearance.
When permitted development applies
- Converting an integral or attached garage to a room within the existing house
- Internal work only (no external enlargement of the building)
- Infilling the garage door opening with a wall and window (this is not classed as an enlargement)
- Not a listed building, and no condition on the planning permission requiring the garage to remain as parking
When planning permission is required
- The original planning permission for the property included a condition requiring the garage to remain as parking (common on new builds from the 1980s onwards)
- Listed building (also requires listed building consent)
- Converting a detached garage into a fully self-contained dwelling with its own address and separate services
- Conservation areas: internal conversion is still PD, but a dramatically different frontage (e.g. large glazed screen where a garage door was) may need planning permission
Check for planning conditions before starting
Many new-build properties have a planning condition requiring the garage to remain available for parking. This is attached to the original planning permission, not to the title deeds. Check the original planning permission via your borough's planning portal, or ask your solicitor to check the title register. This is the most common planning issue that catches homeowners by surprise.
Not sure if your garage conversion needs planning permission? Our AI checks your property, planning conditions, and conservation area status.
Check now — it is free →Building Regulations: What Every Conversion Must Meet
Building regulations are required for all garage conversions to habitable use, regardless of planning status. Building control inspects at key stages and issues a completion certificate at the end. This certificate is essential when you sell.
Floor
Garage floors are typically concrete slabs without a damp-proof membrane. For habitable use you need:
- A DPM (damp-proof membrane) below or on top of the existing slab
- Rigid insulation (typically 75–100mm PIR) to achieve U-value 0.25 W/m²K or better
- Sand/cement screed or floating timber deck to give a level finish
- Floor level check: an integral garage floor is often 100–200mm lower than the house. Account for the insulation and screed buildup in your headroom and threshold details.
Walls
- Existing walls must achieve U-value 0.28 W/m²K or better (usually requires 50–75mm insulation installed internally)
- The party wall between the garage and house must be fire-resisting (typically already 100mm blockwork, confirmed by building control)
- Any new wall infilling the garage door opening must achieve U-value 0.18 W/m²K
Roof and ceiling
- Roof insulation must achieve U-value 0.18 W/m²K or better
- For an integral garage with habitable space above: the ceiling must achieve at least 30 minutes fire resistance (REI 30)
- If the existing garage roof is flat and in poor condition, replacement is often done at this stage
Ventilation
- Habitable rooms: background ventilation (trickle vents in windows) and openable window of at least 1/20th of floor area
- Bathrooms and kitchenettes: mechanical extract ventilation (15 l/s for bathrooms)
Fire door (integral garage)
The door between the integral garage and the house must be a FD30S fire door if it is not already. This is a standard requirement and costs £300–£600 supply and fit including the frame upgrade.
Structural (if room above)
A structural engineer must confirm the floor between the garage and the room above can carry habitable loads (1.5 kN/m² live load). Many integral garage ceilings already meet this. Get written confirmation before building control approval is submitted.
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Key Design Decisions
What to do with the garage door opening
The garage door opening is typically 2.1–2.4m high and 2.4–3m wide. Three options:
Infill with wall and window (most common)
Brick or block wall with one or two windows. Matches the existing house, best thermal performance, cheapest option. Cost: £3,000–£5,500.
Full or part glazing
Replace the garage door with bi-fold or sliding glazed doors. Creates an excellent home office or garden room feel with a connection outside. Works well facing a garden or courtyard. Facing the street, consider privacy. Cost: £5,000–£10,000 for a glazed system.
Retain an insulated garage door
An insulated sectional door can be retained for a gym, workshop, or flexible space. Does not meet habitable room thermal standards (U-value around 1.0–1.5 W/m²K) but may be acceptable for non-habitable uses. Building control will advise on what is acceptable for your intended use.
Heating options
- Extend existing central heating: add a radiator on the existing circuit. Simple and cheap if the boiler has capacity. Cost: £500–£1,200 per radiator installed.
- Wet underfloor heating: ideal if laying a new screed floor. Even warmth, no wall space taken by radiators. Cost: £2,000–£4,000 including manifold.
- Electric underfloor or panel heater: cheapest to install, more expensive to run. Suitable for a home office used only during working hours.
Realistic Timeline
Design and drawings
1–3 weeksGarage conversions rarely need an architect. A builder or building regulations specialist can produce the required drawings. More complex conversions (structural changes, annex) benefit from an architect.
Building regulations
2–4 weeksFull plans submission to local authority building control or private approved inspector
Construction (basic room)
4–7 weeksFloor preparation, insulation, infill, plastering, electrics, heating, decoration
Construction (with en-suite or annex)
7–12 weeksAbove plus drainage, first fix plumbing, bathroom tiling and fit-out, kitchen installation
Total project
6–16 weeksSimple home office: 6–8 weeks. Bedroom with en-suite: 10–13 weeks. Full annex: 12–16 weeks. No party wall process and no planning application in most cases.
Common Mistakes
Not checking for planning conditions on the garage
Many properties (particularly those built from the 1980s onwards) have a planning condition requiring the garage to remain available for parking. This is on the original planning permission, not the title deeds. Check the planning portal for your address before starting any work.
Underestimating the floor level difference
An integral garage floor is often 100–200mm lower than the house floor. After adding DPM, insulation, and screed (typically 100–130mm total), the finished level may still be 50–100mm lower. This creates a step and affects headroom. Measure before specifying the floor buildup.
Skipping building regulations to save money
Some builders offer to skip building regulations. This saves £600–£1,000 upfront but creates a serious problem when you sell. Solicitors request the completion certificate. Without it, buyers either pull out or require an indemnity insurance policy. Always use building regulations.
Poor thermal bridging at the garage door head
The lintel above the garage door opening is a significant thermal bridge. When infilling the opening, insulation must continue above and around the lintel to prevent cold spots and condensation. This detail is often missed. Specify it explicitly in the drawings.
Converting to a self-contained annex without checking planning
A garage used as an annexe forming part of the main dwelling is generally fine under permitted development. A fully self-contained unit with independent access, address, and services may require planning permission as a change of use. If you plan to let it separately, speak to a planning consultant before starting work.
Frequently Asked Questions
How much does a garage conversion cost in London in 2026?
All costs inc VAT: basic home office or gym £18k–£30k, bedroom or playroom £22k–£35k, bedroom with en-suite £32k–£50k, full annex with bathroom and kitchenette £40k–£70k. Cost per m² is £1,100–£3,500 depending on specification. Garage conversions cost 2–3x less per m² than a new extension because the structure already exists.
Do I need planning permission for a garage conversion in London?
Most garage conversions do not need planning permission. Converting a garage to habitable space within the same house is permitted development provided no external enlargement takes place. You do need planning permission if: the original planning permission includes a condition requiring the garage for parking, the property is listed, or you are converting to a fully self-contained dwelling.
Do I need building regulations for a garage conversion?
Yes, always. Building regulations are required for all garage conversions to habitable use. Key requirements: floor DPM and insulation, wall insulation, roof insulation, ventilation, fire door between garage and house, electrics to Part P. The completion certificate is essential when you sell.
How long does a garage conversion take?
Design and building regulations: 3–6 weeks. Construction: 4–7 weeks for a basic room, 7–12 weeks if adding an en-suite or kitchenette. Total project: 6–8 weeks for a simple office, 12–16 weeks for a full annex. There is no party wall process and usually no planning application, making garage conversions one of the quickest routes to new space.
Will a garage conversion add value to my property?
Yes, typically 5–15% in London depending on use and finish. An additional bedroom with en-suite gives the strongest return in most London markets. In areas where off-street parking is very scarce, losing the parking space may reduce the uplift. An annex that generates rental income can add significant value beyond the capital appreciation.
What is the best use for a garage conversion in London?
It depends on what the house lacks. If short on bedrooms, a bedroom with en-suite adds the most value. If bedrooms are sufficient, a home office is the most in-demand use and the cheapest to build. A full annex gives the highest financial return but costs the most and may need planning permission if fully self-contained.
Can I convert a garage into a self-contained annex?
Yes, but check the planning rules first. An annexe used as part of the main dwelling (for a family member) is generally permitted development. A fully self-contained unit with its own address, independent access, and separate services may require planning permission as a change of use. Speak to a planning consultant before proceeding if you intend to let it independently.
Do I need a structural engineer for a garage conversion?
Only in specific situations: if there is habitable space above the garage and you need to confirm the floor can carry habitable loads; if you are removing or altering load-bearing elements; or if adding a bathroom significantly increases floor loading. For a basic room or office conversion with no structural changes, a structural engineer is not usually needed.
Summary
A garage conversion is the fastest and most cost-effective route to additional habitable space in London. At £1,100–£2,500/m², it costs a fraction of a new extension. Most conversions are permitted development. The main process requirement is building regulations, not planning.
Check for planning conditions on your property before starting. Get building regulations approval and keep the completion certificate. The quality of the thermal envelope determines whether the space is comfortable to use year-round.
A bedroom with en-suite maximises value. A home office maximises practicality for the lowest cost. A full annex maximises return if you need rental income or space for a family member.
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