What can a double garage become?
A double garage in a typical detached house measures around 5.5m × 5.5m to 6m × 6m. That's enough for almost anything:
- Two separate rooms — a home office and a bedroom, a gym and a utility room, a playroom and a study — each with its own window and door.
- A master suite with bedroom, walk-in wardrobe and en-suite.
- A self-contained annexe with bed-sitting room, shower room and kitchenette for a relative or lodger — see our annexe page.
- A large open-plan family room, cinema room or games room.
- A half conversion: one bay converted into a room, one bay kept as a garage with the door retained. This is popular where parking is tight or you have a car worth keeping under cover.
Things that are different about a double garage
A double garage conversion is not simply two single conversions side by side. The wider front opening (often 4.5–5m) needs a new lintel or steel to support the wall above when the door is removed and replaced with windows and brickwork. The larger floor area makes underfloor heating more worthwhile. Detached double garages need their foundations, roof and structure assessed, and sometimes upgraded, before conversion. And if you're creating an annexe, planning permission is more likely to be needed. We cover all of this at the survey and design stage.
What's included
- Removal of one or both garage doors and construction of insulated, brick-matched infill walls with new windows or doors.
- New lintels or steel beams as required, designed by a structural engineer.
- Raised, insulated and damp-proofed floors; insulated walls and ceilings to Building Regulations standard.
- Internal partitions, doorways and fire separation to suit the layout you choose.
- Electrics, heating (radiators or underfloor), plumbing and drainage for bathrooms, kitchenettes and utility areas.
- Plastering, flooring, decoration and second-fix joinery.
- Building Regulations notice, inspections and completion certificate.
Double garage conversion cost
A full double garage conversion into two rooms or a master suite typically costs £16,000–£26,000. A half conversion (one bay) costs about the same as a single garage conversion, £8,000–£14,000. Annexes with kitchens and bathrooms are £28,000–£45,000. Detached garages needing structural or roof upgrades cost more — we'll tell you exactly what's required before you commit. See the full cost guide.