Is my detached garage suitable for conversion?
Detached garages fall into two groups. Brick or block-built garages with proper foundations and a tiled or felted pitched roof are excellent candidates — they can be insulated, damp-proofed and fitted out like any other conversion. Prefabricated concrete-panel garages(the sectional type with a corrugated asbestos-cement or steel roof) are generally not worth converting: the panels are thin, the roof needs replacing and the base is usually a thin slab. In those cases it's better to remove the garage and build a new insulated garden room on the same footprint, which we can also do.
Our free survey looks at foundations, wall thickness, roof condition and timber, floor slab, damp, drainage and the route for services from the house. We then tell you honestly whether to convert, upgrade or rebuild.
What can a detached garage become?
- Garden office or studio — separate from the house, quiet and professional, with its own entrance for clients.
- Gym, hobby room or workshop with heavy-duty flooring and the right power supply.
- Guest room or teenager's den, with or without a shower room.
- Self-contained annexe with bedroom, shower room and kitchenette — read our annexe guide, because planning rules are stricter for separate buildings.
Services, insulation and roof
A detached garage has to be treated as a small building in its own right. We typically run a new armoured electrical supply from the house consumer unit, insulate the roof (either at rafter level to create a vaulted ceiling or with a new insulated flat ceiling), insulate walls internally or externally, lay a new insulated floor over the slab, and fit a proper insulated door and double-glazed windows. Heating is usually electric — underfloor or panel heaters — unless the garage is close enough to the house to extend the central heating. Water and drainage can be brought in for a shower room or kitchenette if the run to a drain is practical.
Planning permission for a detached garage
Converting a detached garage into an office, gym or hobby room used by your household is usually permitted development, provided the building remains "incidental" to the house. Converting it into sleeping accommodation or a self-contained annexe changes its use and usually needs a planning application — as does any increase in height or footprint. Listed buildings and conservation areas have extra rules. We'll advise at the survey and handle any application. More on planning.
Detached garage conversion cost
A brick-built single detached garage converted into an office, gym or studio typically costs £10,000–£16,000, reflecting the extra roof insulation and the new electrical supply. Adding a shower room or kitchenette increases this, and a full annexe in a detached double garage is typically £30,000–£50,000. If the garage needs a new roof or the base is unsuitable, we'll quote for the upgrade separately so you can compare it with a rebuild. Cost guide.