What the job involves
A garage conversion turns a space built for a car into a proper habitable room, such as a bedroom, home office, playroom, utility room or extra living space. This guide covers integral garages (under the main roof of the house) and attached garages (joined to one side). Both are usually cheaper to convert than building an extension, because the shell already exists. They still need more work than most people expect.
A garage is built to a much lower standard than a living room. The walls are often single-skin brick or thin blockwork, the floor is a bare concrete slab that may sit lower than the house, and there is little or no insulation. The big door opening is only a thin door in a frame. A conversion has to fix all of this.
Typical work includes:
- Removing the garage door and building up the opening with a new wall, usually with a window.
- Checking or adding a damp-proof membrane to the floor, then insulating and screeding or boarding it so it sits level with the house.
- Insulating walls and ceiling and fitting a vapour-appropriate lining.
- Extending or adding heating, usually radiators from the main system or electric heating.
- New electrics: sockets, lighting, possibly a new circuit, and smoke detection.
- Plastering, decorating and flooring.
- Making sure there is adequate ventilation, a safe escape route, and fire protection between the new room and the rest of the house.
Conversions need building regulations approval, even when planning permission is not needed. Check too whether your original planning permission has a condition requiring the garage to stay available for parking. Your local council can tell you.
What affects the price
No two garages are the same, which is why the prices on this page vary. These are the things that move the cost most:
- Size of the garage. A double garage means more floor, wall and ceiling to insulate, more finishing, and more heating than a single.
- Condition of the floor. If the slab is damp, cracked or well below house level, the build-up needed to bring it up takes more materials and labour.
- The garage door opening. Filling it in with a insulated cavity wall, new lintel checks, matching brick and a new window costs more than a simple stud infill. Matching bricks on a visible front wall is often fussy work.
- Structure above. If there is a bedroom over the garage, or the door opening carries a load, you may need an engineer's calculations and steelwork.
- Services in the way. Boilers, gas or electric meters, consumer units and pipework are common in garages. Moving them adds specialist work and cost.
- What the room will be used for. A bedroom needs more thought on escape and fire safety than a store or office. A utility room or shower room needs plumbing and drainage, which can add significantly.
- Heating and electrics. Extending a radiator circuit is different from fitting separate electric heating. A new circuit or consumer unit upgrade adds cost.
- Level of finish. Skirting, a new internal door, built-in storage, flooring choice and decoration all vary widely.
- Windows and doors. The size, number and type of glazing, and whether you want patio doors, change the price.
- Access and location. Tight access, parking restrictions and local labour rates all play a part.
- Professional fees. Drawings, structural calculations and building control fees are small compared with the build but should not be forgotten.
Ways to keep the cost down
- Keep the room use simple. A home office or playroom costs less than a bedroom with an en suite.
- Leave services where they are if you can. If a boiler is in the garage, consider boxing it in with a fire-rated partition rather than moving it.
- Decide the layout before work starts. Changes once walls are up cost far more than changes on paper.
- Choose a sensible window size and position rather than a large bespoke unit.
- Do the decorating yourself, but leave insulation, electrics and structural work to professionals.
- Get several itemised quotes and compare like with like, not just the bottom line.
- Plan the conversion outside the busiest building season if you can be flexible, as some builders have more availability then.
- Order flooring, radiators and fittings yourself only if your builder agrees, so there is no dispute over responsibility.
What should be included in a quote
A proper quote should be in writing and itemised. Look for:
- [ ] A clear description of the work, room by room and stage by stage
- [ ] Floor treatment: damp-proofing, insulation, screed or boards, and the finished level
- [ ] Wall and ceiling insulation, and the lining and plastering to be used
- [ ] The door opening: structure, wall construction, brick or render finish, and window specification
- [ ] Heating: what is being fitted and who is doing the work
- [ ] Electrical work, including testing and certification
- [ ] Plumbing and drainage if applicable
- [ ] Ventilation and smoke or heat alarms
- [ ] Building regulations application, inspections and the final completion certificate, and who pays for them
- [ ] Structural calculations or engineer's fees if needed
- [ ] Skip hire, waste removal and making good outside
- [ ] Decorating, flooring and finishing, and exactly what is excluded
- [ ] Payment schedule tied to stages of work
- [ ] Start date, expected duration, insurance details and guarantee terms
- [ ] How extras and variations will be priced and agreed
Questions to ask a builder
- Have you converted garages like mine before, and can I see or speak to someone whose job you did?
- Who deals with building control, and will I get the completion certificate?
- How will you deal with the floor level and damp?
- What will you do about the door opening, and how will the outside look?
- Do I need an engineer, and is that in the price?
- Are the gas and electrical workers suitably registered? Gas work should be done by a Gas Safe registered engineer, and electrical work must meet Part P requirements.
- What is not included, and what could push the price up?
- Who is on site day to day, and what happens if something unexpected turns up?
- How do you protect the rest of the house from dust?
How long it takes and what to expect
Most garage conversions take a matter of weeks rather than days, and longer if there is structural work, plumbing or a complicated finish. The usual order is: opening up and preparation, structural work and infill, floor, first-fix electrics and plumbing, insulation and boarding, plastering, second fix, then decorating and flooring. Plaster and screed need drying time, which can hold up the finishing stages.
Expect noise, dust and some disruption, particularly if the garage is integral and you share walls and a door with it. Building control inspectors will visit at set stages, and the work should not be covered up until they have seen it. Tell your insurer and, if you have one, your mortgage lender about the change. When the work is done, keep the completion certificate safe, as a buyer's solicitor will ask for it later.
Signs a quote is too cheap or too expensive
Possibly too cheap:
- No mention of building regulations, or an offer to "skip" building control
- No floor insulation or damp-proofing listed
- A vague one-line description with no breakdown
- Large payment up front, or pressure to accept quickly
- Nothing for the door opening finish, window or making good outside
- No insurance or no willingness to provide references
Possibly too expensive:
- Large unexplained allowances or a heavy "contingency" with no detail
- Specifications far above what you asked for
- Charges for services you do not need, such as moving a boiler that could stay
- A price much higher than the others with no clear reason, such as structural work the rest left out
If quotes differ widely, ask each builder to explain the gap. Often one has included something the others missed. Compare your quotes against the prices on this page to see how they sit against what other homeowners paid.