Double Garage Conversion — Why the Extra Space Opens Up Options That a Single Does Not

A double garage — typically 48–60 square metres — is large enough to convert into a meaningful living space: a large open-plan room, two separate rooms, a bedroom with en-suite, or a substantial home office with storage. The extra floor area also means the conversion cost per square metre is usually lower than for a single garage, though the total spend is higher. The challenge is making decisions early about how the space will be used, since those decisions affect structural work, drainage runs, and electrical layout in ways that are expensive to change later.

Converting the Whole Space or Part of It

Many homeowners convert a double garage into a single-car garage with an additional room — retaining a parking space while gaining living area. This is a practical compromise, particularly where off-street parking is valued or where permitted development rights are conditioned on retaining a parking space. The dividing wall between the retained garage and the new room must meet the same building regulations standards as any habitable room partition. The boundary between the two spaces needs careful attention: sound insulation, fire separation if required, and the thermal envelope of the conversion must be maintained at the wall.

Structural Considerations

Double garage doors typically span the full width of the opening — sometimes 4.5 to 5.5 metres. The lintel above this opening must be assessed before the doors are removed and the opening infilled. In many cases the existing lintel was designed to carry only the weight of the doors and not the masonry that will be added above it when the opening is infilled. A structural engineer's assessment of the lintel and the wall above it is advisable before work begins. This is not a significant cost — a structural engineer's report for a garage conversion is typically £200–£500 — but omitting it is a significant risk.

Drainage for a Bathroom or WC

If the conversion includes a bathroom, WC, or utility room, drainage must be considered at the design stage. The existing concrete slab will need to be broken out and drainage channels formed before the new floor is laid. This work is far more disruptive and expensive if it is addressed as an afterthought once the floor has already been finished. If there is any possibility of wanting a bathroom or WC in the space — even if not immediately — plan the drainage run from the outset and cap it off if not immediately used.