How much does a garage conversion cost?

Converting a two-car garage into a habitable room in the UK usually costs between £10,000 and £25,000, and a self-contained annexe with its own kitchen and shower room can pass £30,000. Where you land depends on insulation, heating, wiring, glazing, damp proofing and whether the floor and roof need work. Below we break the numbers down and show what you give up.

Where the money goes in a two-car conversion

For a straightforward habitable room, most two-car conversions land between £10,000 and £25,000. A simple home office or playroom sits at the lower end. A bedroom with an en-suite, or a room that needs the floor lifting and re-laying, sits higher. Turn it into a self-contained annexe with a kitchen and a bathroom and you can go past £30,000 once you add drainage, a second means of escape and full sign-off.

Those figures are third-party build costs, not our prices. They come from the trades who do the work: a builder or joiner, an electrician, a plasterer, and sometimes a plumber and a heating engineer. Day rates matter. A general builder in most of the UK charges around £200 to £300 a day, and a two-car conversion typically runs two to four weeks of labour depending on complexity.

The single biggest variable is scope. "Convert my garage" can mean anything from lining the walls and adding a socket, to a fully insulated, watertight, signed-off living space with heating and glazing to match the house. Two quotes that look wildly different are usually pricing two different jobs, so read what is actually included before you compare the totals.

The condition of the existing garage sets your starting point. A single-skin garage with a cold, uninsulated concrete floor and a leaky up-and-over door needs far more work than an attached garage that already shares a wall and a roof with the house. If the slab is sound and level, you can insulate over it. If it is cracked, damp or well below the house floor level, you may have to break it out and re-lay, which adds cost and time.

Damp is the quiet budget killer. A garage floor with no damp-proof membrane will need one before you put down insulation and a finished floor, and any damp in the walls has to be traced and stopped first. Heating is the next lever. Extending the house central heating with an extra radiator is often £400 to £700 if the boiler has the capacity, whereas a full electric heating and hot-water setup for an annexe costs a good deal more.

Glazing and the door opening swing the number too. Bricking up or building a knee wall under the old door, then fitting a window or French doors, is skilled work and the frames are not cheap. Finally, whether you need building control sign-off adds fees and the cost of doing everything to standard, from insulation U-values to fire safety and ventilation.

Most garage conversions do not need planning permission, but nearly all of them need building regulations approval. These are two separate things and people mix them up constantly. Planning permission is about what you are allowed to build and how it affects neighbours and the street. Building regulations are about how the work is done: insulation, fire safety, ventilation, electrics and structure.

Converting the inside of an existing garage is usually permitted development, so no planning application is needed, as long as you are not extending the footprint or changing the use in a way your area restricts. Flats, listed buildings, conservation areas and some new-build estates carry conditions that remove permitted development rights, so always check your title and any planning conditions before you start.

Building regulations almost always apply because you are creating a habitable room out of a space that was never meant to be lived in. The 30 square metre figure people quote is a building regulations threshold for certain outbuildings, not a planning limit, and it does not get you out of proper sign-off on a conversion. Use building control and get the completion certificate. Without it, the conversion can hold up a future sale.

A habitable room and a self-contained annexe are very different jobs, and the price gap reflects that. A habitable room, an office, gym, playroom or bedroom, borrows heating and services from the house and shares its front door. That keeps costs at the lower end of the range because you are insulating, lining, wiring and finishing a box that is already attached.

An annexe is effectively a small dwelling. It needs its own kitchen and bathroom, hot and cold water, waste drainage, sometimes a separate electricity supply, and a compliant means of escape. Drainage alone can be a surprise if the nearest soil pipe is on the far side of the house. Each of those additions carries labour, materials and inspection, which is why an annexe pushes well past a simple room.

Be honest about what you are really building. If you want somewhere to work or a spare bedroom, a habitable room is enough and much cheaper. If you want a space a relative can live in independently, budget for the annexe and expect the build to take longer and involve more trades.

The hidden cost of any garage conversion is the space itself. The moment the room is finished, the parking and storage that garage gave you are gone. That sounds obvious, but it is the thing people regret most a year later, and it never shows up on the builder's quote.

A two-car garage is a huge amount of dry, secure, weatherproof storage. It holds the mower, the bikes, the tools, the Christmas boxes, the spare tyres and everything else that does not belong in the house. Convert it and all of that has to go somewhere. Usually it ends up cluttering the new room, filling the loft, or piling up in a corner of the garden under a tarp.

Parking matters at resale too. In areas where off-street parking is tight, losing it can cancel out the value your new room adds, because buyers with two cars simply walk away. Before you convert, work out where the cars and the stuff will actually live afterwards. If the answer is "nowhere", that is a real cost even though it has no invoice attached.

A well-finished, properly signed-off conversion usually adds value, especially where it turns unused space into a room the house genuinely needs, like a fourth bedroom or a home office. The gain is strongest when the work is done to standard and the completion certificate is in the file. Cut corners or skip building control and you can actually reduce the value, because a surveyor or solicitor will flag the missing paperwork.

The value picture is local. In a family area where bedrooms are gold, converting an underused garage can pay for itself and more. In an area where every house has two cars and nowhere else to park, the lost parking can wipe out the gain. We cover the numbers in more detail in our guide on how much value a double garage adds, and it is worth reading before you decide.

The comparison people forget is the one against keeping the garage. A tidy, working two-car garage is itself a selling point. So the honest question is not "does a conversion add value", it is "does a conversion add more value than the garage it replaces". Sometimes yes, sometimes clearly no.

If you like the extra room but hate losing the garage, the neat fix is to convert the old space and build a new concrete garage elsewhere on the plot. That gives you the living space you wanted and puts the parking and dry storage straight back, often for a lot less fuss than trying to squeeze both out of one building.

A new sectional concrete garage goes up quickly and sits on a poured concrete base. That base is the non-negotiable part. A concrete building always needs a proper slab, 100mm thick and 150mm wider and longer than the building overall, cured for about a week before installation. Paving slabs, gravel, timber bearers and plastic grids are fine under a light timber shed, but they are never an option under a concrete building. Thickening the outside edge of the slab to 150mm is better but optional, and most builders pour a flat 100mm slab unless you ask.

This is where the maths often works in your favour. You get a room in the house from the conversion, and a fresh, secure garage for the cars, the bikes and the boxes. If you are weighing it up, our guide on the cost to turn a double garage into a room sits alongside this one, and our concrete garage buying guide walks through sizes, doors and finishes so you can see what a replacement would involve.

A two-car garage conversion in the UK usually costs between £10,000 and £25,000 for a habitable room, rising past £30,000 for a self-contained annexe with a kitchen and bathroom. The price is driven by the state of the floor, damp proofing, insulation, heating, glazing and whether you need building control sign-off, which nearly every conversion does. Most conversions are permitted development and need no planning permission, but that is separate from building regulations, and the 30 square metre figure is a building regs threshold, not a planning one. The real hidden cost is the storage and parking you lose the day the room is finished. Before you commit, work out where the cars and the clutter will go. If the answer is nowhere, a common fix is to convert the old space and build a new concrete garage on the plot, putting the parking and dry storage straight back.