Converting a garage into a room: what is actually involved

Short answer: a garage conversion is a change of use under the building regulations, so the floor, walls and roof all have to be brought up to the standard of a habitable room and signed off by building control. Planning permission is usually not needed for an attached garage as long as the work is internal and there is no planning condition keeping it as parking. Most of the cost is in the floor and walls, which is the part not to skimp on.

Step by step

1. Check the planning history. Some newer estates have a condition on the original permission requiring the garage to stay as parking. Conservation areas and flats also need an application. We look this up for the address before quoting.
2. Building control application. Either a full plans application or a building notice. Building control inspects the floor, the damp-proofing, the insulation and the structure at stages, and issues a completion certificate at the end.
3. Strip out. The garage door comes out, anything stored goes, and the slab and walls are checked for damp and level.
4. The floor. Garage floors are usually a step down from the house and have no damp-proof membrane. The usual fix is a new timber floor on joists over a membrane with insulation between, boarded with moisture-resistant board, bringing it level with the hall. On our house on Kingfield Road that is 150 by 50 joists with the floor raised about half a metre to meet the hall. The alternative is an insulated screed over a membrane where the levels allow.
5. The walls. A single-skin or uninsulated cavity wall is lined internally with insulated studwork. Ours is a 100 by 50 stud lined with 90 millimetres of rigid insulation. The ceiling gets insulation between and under the joists.
6. The opening. The garage door opening is bricked up to match the house with a new window and, where wanted, a door. Matching the brick and the window style is what stops a conversion looking like a conversion.
7. Services. A radiator or a heating zone off the existing system, sockets and lighting by our electrician, and plumbing for a shower room or WC if there is one. A soil connection is the thing to check early: if the drains are a long way off, it changes the plan.
8. Finish. Plasterboard and skim, skirtings and architraves, an internal door into the house, and a mains smoke alarm linked to the rest of the house if the room is a bedroom.
9. Sign-off. Final inspection and completion certificate.

Can it be a bedroom?

Yes, if it is built to that standard: an escape window or a protected route out, a linked mains smoke alarm, and the same insulation and ventilation as any bedroom. We build to that standard by default, so a home office can become a bedroom later without redoing the work.

What goes wrong on cheap garage conversions

• No membrane or insulation in the floor, so the room is cold and the carpet is damp within a winter.
• Walls dot-and-dabbed straight onto the single-skin brick with no insulation.
• A window that does not match the house, so the conversion is obvious from the street and a buyer’s surveyor flags it.
• No building control sign-off, which a buyer’s solicitor will ask about and an indemnity policy only partly fixes.

Cost

We do not have enough standalone garage conversions on the books to publish an honest range, so we quote after a site visit rather than borrow a national average. Tell us what the room is for and we will walk the garage with you. Service page: garage conversions in Liverpool and Merseyside.