Building a room over your garage: the checks that come first

Can the existing walls and foundations take the load?

A garage built with half-brick or single-skin block walls on shallow footings will not usually carry a new floor, walls and roof without strengthening. The usual route is trial holes to expose the foundations, followed by an engineer's assessment. The answer ranges from reuse as-is, through thickening walls or adding piers, to rebuilding the garage walls completely.

Knowing this early is the single biggest factor in whether the project makes sense. It is far cheaper to find out with a trial hole than after the drawings are approved.

• Wall construction: single skin, cavity or solid
• Foundation depth and condition from trial holes
• Any cracking or movement already present
• Drainage runs close to or under the garage

Fire separation between garage and room above

If the garage stays in use for a car, building regulations require fire-resisting construction between it and the habitable room above — typically a specified ceiling build-up and attention to any openings into the house. The internal door from garage to house also needs to meet fire requirements.

If you plan to convert the garage at the same time, the fire strategy changes, and it is worth deciding that before drawings are done.

Headroom, floor level and the stairs

The new first floor needs to line up with the existing landing, or accept a step. Garage ceilings are sometimes lower than house ceilings, which pushes the new floor down or the ridge up. Access is usually through the existing landing — check which room loses space for the new doorway.

The roof form matters too. Matching the main house roof pitch generally looks best but raises the ridge, which affects neighbours and planning.

Planning and building control

A two-storey side addition often needs planning permission, particularly where it sits close to a boundary or faces a road. Your local council — Torbay, Teignbridge or South Hams in our area — decides. Building regulations approval is required in all cases for structure, fire, insulation and escape.

On attached houses, work on or near a shared wall may also need party wall notices.

Insulation and the cold garage below

A bedroom above an unheated garage has a cold floor unless the new floor is properly insulated. The floor build-up has to satisfy both thermal and fire rules while keeping headroom, which is why it is designed rather than improvised.

When it is not the right answer

If the garage walls need complete rebuilding, the project becomes a full two-storey side extension with a garage underneath, and should be priced as such. Sometimes a loft conversion or a rear extension gives the same space more simply. We will say so on the site visit rather than push a particular route.

Anthony handles these jobs directly with our own team, from groundworks to the final carpentry and plastering.

Common questions