Garage conversions: a pricing walk-through

Garage conversions have a reputation as the easy money of domestic building: no dig, no roof, walls already standing. Sometimes that is true. But the price lives in the details of a structure that was built to house a car, not a person, and the difference between a profitable conversion and a painful one is usually decided at the survey. Here is the walk-through, in pricing order.

Step one: survey the box you have been given

Before a single rate matters, walk the garage with a critical eye. Is it attached or detached? Single skin brickwork or cavity? What is the floor: a sound level slab, or a cracked one that falls towards the door? Is there any damp proofing at all? Where do the services already run? Is the roof structure sound and insulable? Twenty minutes here, following something like our site survey checklist, tells you which of the cost blocks below are in play.

Step two: the opening, the infill and the structure

The garage door opening is where the structure earns attention. The new infill wall needs its own foundation in many cases, because the slab edge under the door was never designed to carry masonry. The existing lintel over the opening may be fine for a door but need checking for the new arrangement. If the client wants the opening widened into the house, add a steel and the temporary works that come with it. This block is small in area and large in consequence: get the foundation detail wrong and the crack appears above the new window a year later.

Step three: floor, damp and the ground you cannot argue with

Garage slabs are usually lower than house floors, often laid to a fall, and rarely damp proofed. The standard fix is a new insulated floor build-up: damp proof membrane lapped into the walls, insulation, then screed or a timber deck, arriving level with the house floor. Suppose the slab is sound and the level difference is modest: this is routine work. Suppose the slab is cracked, the fall is severe, or levels force a dig-out: the floor becomes one of the biggest lines on the bill. This is the garage conversion's version of groundworks risk, and it deserves the same honesty: state your assumption in the quote and price the discovery separately if you cannot verify it.

Step four: walls, roof and getting to living standard

A single skin garage wall is not a habitable wall. It needs an insulated lining system built inside it, which costs money and steals floor width, or in some cases an upgraded cavity solution. The roof needs insulation to current standards, whether that is between and under a pitched structure or above a flat deck. Windows must meet thermal and safety requirements. None of this is glamorous, and all of it is exactly what building control will look at. The quiet rule: the worse the existing shell, the more the conversion behaves like a deep refurbishment rather than a light one.

Step five: services, fit-out and compliance

Now the room becomes a room. Electrics to current regulations, heating extended from the house or provided locally, ventilation, plastering, flooring, decoration, doors. If the new space is a bathroom, utility or kitchen, the services block grows sharply, exactly as it does in any conversion. And the whole project needs building regulations approval, with the change of use documented, even where planning permission is not required. Pricing the building control fee and the certification visits into the quote is the professional move; leaving them out is how a tidy job ends with an awkward invoice conversation.

The questions around the edges

Two more items belong in the conversation before the number is final. Planning: most attached garage conversions fall under permitted development, but some estates carry conditions requiring the parking to be kept, and detached garages can raise their own questions, so a quick check with the local authority is cheap insurance. And the programme: a straightforward conversion is measured in weeks, not months, which matters to the client's expectations and to your prelims. A garage conversion carries a small but real set of weekly costs, and quoting a realistic duration protects both the relationship and the margin. Finally, ask where the displaced things go: the freezer, the bikes, the tools. It sounds trivial, but the client who realises mid-job that they have lost all their storage is a client looking for someone to blame.

A worked shape, not a price list

Because every garage differs, resist the urge to quote from someone else's total. Instead, suppose a typical attached single garage in decent condition: the bill splits roughly into the infill and openings, the floor build-up, wall and roof insulation with linings, services, and fit-out, with prelims and waste on top. Now stress it: a detached garage adds a longer service run and possibly a new consumer unit feed. A poor slab moves the floor block up the table. A bathroom doubles the services block. The shape of the bill tells you where your risk is before the number does.

This is the kind of measured, itemised quote QS Quoter helps assemble: describe the conversion or upload a drawing, and it builds a draft bill of quantities at your own rates, with a client-ready copy, a private cost copy for you, and every line editable. The judgement about that cracked slab stays yours.