Garage conversion cost by type
Prices are for an integral or attached garage; detached garages may need additional work on walls and roofs. London and South East costs are typically 20-30% higher.
| Conversion type | Typical cost | Notes |
|---|---|---|
| Single garage to habitable room | £6,000 to £15,000 | Insulation, plaster, floor, electrics, window |
| Single garage to home office | £8,000 to £15,000 | As above plus data cabling, quality fit-out |
| Single garage to bedroom (en-suite) | £12,000 to £18,000 | Includes plumbing for shower/WC |
| Single garage to utility room | £5,000 to £10,000 | Plumbing connections, tiling, units |
| Double garage to living space | £12,000 to £25,000 | Per above, larger floor area |
| Garage to self-contained annexe | £20,000 to £40,000 | Kitchen, bathroom, full fit-out |
| Detached garage conversion | £15,000 to £30,000+ | Often needs new services, roof work |
Structural work such as underpinning, damp-proofing, or roof replacement is additional. Always get three quotes and check building regs compliance.
What affects the cost of a garage conversion?
The final price is driven by several factors beyond the basic shell work:
- Current state of the garage: an integral garage in good structural condition with a concrete floor costs less to convert than a detached garage with a flat felt roof and no damp-proof membrane.
- Insulation requirements: building regulations require the floor, walls, and ceiling to meet current thermal performance standards. Floors may need a radon barrier and insulation layer beneath a screed or floating floor.
- Plumbing: adding a WC, en-suite, or kitchenette involves extending the existing waste and supply pipes, which may require breaking up the floor slab.
- Electrical work: a separate consumer unit sub-board, new lighting circuits, sockets, and heating controls are typically needed. All work must be signed off by a Part P registered electrician.
- Windows and doors: replacing the garage door with a window and infill brickwork is usually the most visible part of the conversion and a significant cost driver.
- Fire safety and building regs: if the conversion creates a habitable room adjacent to a main house, fire doors, smoke alarms, and possibly escape windows may be required.
- Specification and finish: a basic conversion with budget flooring and standard fittings is far cheaper than a high-spec office or annexe.
- Location: London and South East labour rates are 20-30% above the national average.
Do you need planning permission for a garage conversion?
In most cases, converting an integral or attached garage into a habitable room is considered Permitted Development and does not require a planning application. However, there are important exceptions. Planning permission is generally required if: your property is in a conservation area or is listed; the conversion involves a material change to the external appearance beyond infilling the garage door opening; your property has had its PD rights removed by an Article 4 direction; or the conversion creates a self-contained annexe used by someone other than the main household.
A detached garage used as a separate dwelling (granny annexe for independent occupation or rental) is more likely to require planning permission and potentially a change of use application. Always consult your local planning authority before starting work.
Note that even where planning permission is not needed, building regulations approval is always required for a garage conversion to habitable use. You must apply to your local authority building control (LABC) or an approved inspector before work starts.
Building regulations for garage conversions
All garage conversions in the UK require building regulations approval, regardless of whether planning permission is needed. This covers: structural integrity of walls and roof; thermal insulation of floors, walls, and ceiling to current Part L standards; ventilation and natural light in habitable rooms; fire safety, including fire-resistant doors where the garage connects to the main house; electrical installation to Part P; and drainage where plumbing is added.
You submit a Full Plans application (recommended, as it checks plans before work starts) or a Building Notice. Your local authority building control officer will make site inspections at key stages. At completion you receive a Completion Certificate, which is essential evidence for mortgage lenders and future buyers.
Failure to obtain building regulations sign-off is a significant issue when you come to sell. Lenders will require either the Completion Certificate or indemnity insurance, the latter of which does not guarantee the work was done correctly.
Pitfall: losing parking and mortgage implications
Before converting your garage, check your mortgage terms and local parking restrictions. Some lenders include a condition that off-street parking must be maintained. In some areas, particularly in London, planning authorities will resist loss of parking spaces through garage conversion. Additionally, if your property is a new-build subject to a covenant requiring a garage, converting it may be a breach of that covenant. Check the title deeds and your mortgage offer before committing.
Model the cost before you buy
Our planner helps you set a realistic refurbishment reserve before you buy. If the property you are considering has an underused garage, add the conversion cost to your budget now and compare the cost per square metre against other ways of adding space.