Garage conversion cost: what the job involves and who is registered to do it

the UK roofing register

• How much does a garage conversion cost
• Garage conversion cost UK
• Garage conversion cost per m2
• Average garage conversion cost
• Single garage conversion cost
• Basement conversion cost
• Cellar conversion cost

How garage and basement conversions works

1. Start with the floor, because it is usually the surprise. A garage floor is normally lower than the house floor, often laid straight onto hardcore with no damp proof membrane, and sometimes falling towards the door. Bringing it up to the house level, dry and insulated, means either a new insulated screed over a membrane or a suspended timber floor, and either way it eats head height. Ask what the quote assumes and what happens if the existing slab has to come out.
2. Price what happens to the door opening. The up-and-over door is a hole the width of the room with a lintel over it that was sized for a garage, not for a wall. Filling it means a new insulated cavity wall on its own foundation, a window or a door in it, and making the outside look like it belongs to the house rather than like a filled opening. That last part is where a conversion is judged from the street.
3. Treat the walls as an uninsulated envelope. Garage walls are often single skin, or a cavity that was never insulated, and they sit on a foundation that may be shallower than the house. Bringing them up to a habitable standard means insulating internally, which loses width, or externally, which changes the elevation. On a single garage a hundred millimetres of internal build up on each side is a noticeable share of the room.
4. Get the services quoted properly. A garage typically has one light and one socket on a spur. A habitable room needs a proper circuit, enough sockets, heating that connects to the house system or stands on its own, and ventilation. Electrical work is notifiable, so the quote should name who certifies it. Extending the wet heating system into a room at the end of a run is a design question rather than an extra radiator.
5. Confirm the approvals before the deposit. Converting a garage into habitable space is building work that needs building regulations approval, and it usually does not need planning permission, with real exceptions: a condition on the original permission that keeps the parking, an Article 4 direction, a listed building, or a conversion that changes the elevation in a conservation area. Both questions are answered before the work, not after.

Insurance and paperwork

Common questions

Does a garage conversion need planning permission?

Usually not, because converting the inside of a garage attached to the house is normally permitted development. What removes that is a planning condition on the original estate permission requiring the parking to be retained, an Article 4 direction, a listed building, or work that alters the elevation in a conservation area. Check for a condition before assuming.

Does it need building regulations approval?

Yes, always. A garage is not habitable space and turning it into a room means new thermal elements, a floor that resists moisture, ventilation, electrical work and often fire separation, all of which are inspected and signed off. The completion certificate is what a buyer's solicitor asks for.

Will I lose much room to insulation?

More than people expect. Insulating internally on both side walls and over the floor can take a hundred millimetres or more from each dimension and from the height. On a single garage that is the difference between a comfortable room and a corridor, which is why the measurement to take is the finished internal size rather than the garage's.

Is it cheaper than an extension?

Substantially, and the reason is that the structure and the roof already exist. What it does not do is add floor area to the house, so it improves how the house lives rather than how large it is, and valuers treat it accordingly.

Registered contractors by region

• Registered roofers in the East Midlands postcode area
• Registered roofers in the East of England postcode area
• Registered roofers in the London postcode area
• Registered roofers in the North East postcode area
• Registered roofers in the North West postcode area
• Registered roofers in the Scotland postcode area
• Registered roofers in the South East postcode area
• Registered roofers in the South West postcode area
• Registered roofers in the Wales postcode area
• Registered roofers in the West Midlands postcode area
• Registered roofers in the Yorkshire and The Humber postcode area