In Kent the biggest swing factors are the state of the existing slab, whether the garage is attached or detached, and how much of the original brick or block skin you can keep. A dry, well-built 1970s or 1980s single garage on a semi in Ashford or Maidstone is a very different job from a damp, low-headroom outbuilding behind an oast or farmhouse near Biddenden.
This page sets out what actually gets priced, not a single number, because a garage conversion genuinely can cost twice as much once heating, damp-proofing and building control requirements are factored in properly.
What's included in a proper conversion versus a quick one
A conversion done to building regulations standard means a new insulated floor build-up (because most garage slabs have no damp-proof membrane or insulation under them), insulated stud walls to the existing masonry, a new insulated ceiling if there's a room in the roof above, a fire door and often fire-rated construction where the garage adjoins the house, and mains electrics with a consumer unit upgrade if needed.
The quick version — carpet straight onto the slab, plasterboard on battens, one radiator — looks similar for a fraction of the cost but fails building control, traps damp in the floor, and will feel cold and clammy within a year or two. We won't quote that version because it doesn't meet the Building Regulations that apply whenever a garage becomes habitable space.
The floor is usually the biggest surprise
Garage slabs are almost always laid lower than the house's ground floor and without insulation or a damp-proof membrane underneath. Bringing the floor up to modern standards means either digging out and re-laying with insulation and a membrane, or building up an insulated floating floor on top — which works but eats into headroom, and headroom is often tight in a single garage to begin with.
In damp-prone plots, common on some of the older Wealden farm conversions and low-lying sites near rivers such as the Beult or Stour, we sometimes recommend a tanking or drainage strategy alongside the floor build-up, which adds cost but avoids a damp problem appearing behind new plasterboard eighteen months later.
Walls, doors and windows
The garage door opening has to become a wall, and that's more than bricking it up. It usually means a new stud or blockwork infill, a window or two to give the room natural light (a habitable room needs it), and matching the external finish to the rest of the house so it doesn't look like an afterthought — render, brick slips, weatherboarding or tile hanging depending on what the house is finished in.
Existing masonry garage walls are typically single-skin block, which has poor thermal performance on its own. Insulating internally with a stud wall and vapour control layer is the usual route, and it's worth doing properly rather than skimping on insulation thickness to save a room's worth of floor area.
Heating, electrics and ventilation
Most garages have no heating and minimal wiring. Extending the central heating system with a new radiator or two is usually more cost-effective long-term than an electric heater, but it depends on how far the pipework has to travel from the boiler or manifold. Electrics need a proper first and second fix — sockets, lighting, and often a smoke detector interlinked with the rest of the house if it's being used as a bedroom or living room.
If the room is going to be an en-suite bedroom or a home gym with a shower, plumbing and extraction get added to the scope, and that's when a garage conversion starts approaching the cost of a small extension.
- Insulated floor build-up with damp-proof membrane
- Insulated stud walls to existing masonry
- New windows and infilled garage door opening
- Central heating extension or new heat source
- Full rewire of the space with certified electrics
- Fire door and fire-rated construction where attached to the house
Planning permission and building control in Kent
Most garage conversions don't need planning permission because they don't change the building's footprint or height — it's a change of use within the existing envelope. The exceptions are listed buildings, properties in a conservation area where the council has removed permitted development rights, and conversions that involve extending or altering the roofline.
What you can't avoid is Building Regulations approval. Ashford Borough Council, Maidstone Borough Council and Tunbridge Wells Borough Council all require sign-off on insulation levels, fire safety, electrics and ventilation for a habitable conversion, and a building control inspector will check the floor and wall build-ups before they're covered up. We manage that process as part of the job so you're not chasing inspection bookings yourself.
What pushes the price up or down
A dry, attached single garage with a decent slab and easy access to the existing heating system is the cheapest scenario. Add a detached garage (needing a new heating source or a long pipe run), a damp slab, a low ceiling that needs the floor level dropping, or a change of external finish to match a period house, and the price climbs.
Access matters more in Kent than people expect — a garage down a narrow lane in a Wealden village with no room for a skip or a delivery lorry adds time and cost that a garage on a modern estate close doesn't.
Common questions
Do I need planning permission to convert my garage?
Usually not, because it's a change of use rather than a change to the building's size or shape. Listed buildings and some conservation areas are exceptions, and if you're also extending or altering the roof, planning is likely to apply. We check this on the first visit before pricing anything.
How long does a garage conversion take?
A straightforward single garage conversion typically runs four to six weeks once work starts, longer if the floor needs digging out, damp-proofing is involved, or the scope includes an en-suite. Detached garages needing new heating or drainage connections take longer.
Can I convert a garage myself and just get building control to sign it off?
You can do some of the work yourself, but the insulation, fire safety and electrical elements need to meet exact standards that building control will check. We often see DIY conversions that fail inspection on floor insulation values or missing fire doors, which then have to be opened back up and redone.
Will a garage conversion add value to my house?
It generally adds usable floor area, which buyers value, but it can also reduce off-street parking, which some buyers see as a downside. Whether it's worth it depends on your street and how much parking is already available.
What's the cheapest way to convert a garage without cutting corners?
Keep the footprint and roofline as they are, use the existing central heating rather than adding a new heat source, and choose an internal finish (plaster and paint rather than bespoke joinery) that keeps decoration costs down. The insulation, damp-proofing and fire safety elements aren't ones to cut back on.