Garage Conversion Costs in Belfast 2026

A garage conversion is the cheapest square metre you will ever add to a house, because you already own the floor, the walls and the roof. It is also the job most likely to be underpriced, because those three things were built to keep a car dry, not to keep a person warm.

Here is what it costs in Belfast in 2026 and where the surprises live.

The 2026 range: £7,500 to £18,000

For a typical single integral garage of 14 to 18m², converted to a habitable room, budget £7,500 to £18,000 in Belfast. That is VAT inclusive and it covers the work, a modest design fee and a contingency.

The bottom of that range is a dry, well-built garage from the last twenty years with a sound slab and cavity walls. The top is a 1970s single-skin block garage with a floor 150mm below the house, no damp-proof course worth the name, and a roof that needs replacing before anything else can happen.

You will not know which one you have until someone competent looks at it. That is the whole story of garage conversions.

Where the money goes

A representative breakdown for a 15m² integral garage:

Add a shower room and you are looking at another £3,500 to £7,000, plus drainage, which in a garage on the wrong side of the house can be the most expensive part of the whole job.

The three things that decide the price

1. The floor

Garage slabs are usually thinner than a house floor, laid to a fall towards the door, sitting lower than the internal floor level, and laid with no insulation and often no damp-proof membrane.

To make it habitable you need a damp-proof membrane, insulation and a new floor deck or screed, all built up to meet the house floor level at the connecting door. On a good slab that is a straightforward build-up. On a slab that is cracked, too thin, or falling the wrong way, it means breaking out and recasting, and that is the difference between £1,300 and £3,000 on its own.

Measure the step down from the hall into the garage before you do anything else. It tells you most of what you need to know.

2. Single-skin walls

A great many garages in Belfast and across Northern Ireland — particularly detached and semi-detached garages from the 1960s to the 1980s — are built in single-skin blockwork. One leaf of block, no cavity, no insulation, and no resistance to driving rain in a climate that supplies plenty of it.

You cannot line a single-skin wall with plasterboard and call it a room. The options are an internal insulated stud or an insulated board system with a proper cavity or drainage detail behind it, or in bad cases rebuilding the outer leaf. Either way it costs more, and it eats into the floor area you are converting.

An integral garage inside the main envelope of the house is usually cavity-built and far more straightforward. That is why integral conversions sit at the cheaper end.

3. Foundations

Garage foundations are frequently shallower than those required under a habitable room. Building control will want to be satisfied about them, particularly where the garage door opening is being infilled with a new wall that has to carry load.

Sometimes that means a trial hole and a nod. Occasionally it means underpinning, which changes the economics of the job entirely. Ask the question early.

The garage door opening

Infilling the opening properly means a foundation for the new wall, a cavity wall built off it, a lintel over the new window, a cavity closer and a damp-proof course tied into what is already there. Done well it is invisible from the street. Done badly it is a permanently damp patch under the window and an obvious rectangle of slightly different render.

If you want the room to look like it was always a room, this is where to spend the money. Match the render or the brick, keep the window proportions consistent with the rest of the elevation, and do not leave the concrete apron running up to a wall.

Damp, ventilation and the Northern Ireland climate

Garages breathe. They are draughty by design, which is why they rarely feel damp even though they are wet. Seal one up, insulate it and put a person in it, and the moisture that used to blow through now condenses on the coldest surface it can find.

The fix is proper insulation with the right detailing, a continuous damp-proof membrane and background ventilation. This is exactly the sort of thing building control is for. It is also why an internally insulated wall needs to be designed rather than improvised — the same physics that governs loft insulation applies to a wall, and getting the layers in the wrong order creates a problem you cannot see until the wallpaper lifts.

Planning permission: usually not, with one big exception

Converting a garage is normally internal work plus an alteration to an elevation, and in most cases it falls within permitted development. Replacing a garage door with a window and a panel of wall is an alteration, not an extension.

The exception is a planning condition. A great many housing developments in Northern Ireland were approved on the basis of a specified number of off-street parking spaces, and carry a condition requiring the garage to be retained for parking. If your house has one of those conditions, converting the garage without permission is a breach of planning control, whatever the permitted development rules say.

Check the original planning approval for the estate before you commit. Conservation areas, areas of townscape character, listed buildings and Article 4 directions also cut back permitted development rights — our guide to planning permission in Northern Ireland sets out where those lines fall.

Building control: always

Converting a garage into a habitable room is a change of use and it needs building control approval from your district council, without exception. The officer will be looking at:

• Floor, wall and roof build-ups meeting the required thermal performance
• Damp-proofing and ventilation
• Structural adequacy of the new opening infill and the existing foundations
• Means of escape, particularly if the room is to be used as a bedroom
• Electrical work and alarm coverage

You will get a completion certificate at the end, and you will want it — a converted garage with no certificate is a line in a solicitor's enquiries when you sell. Our guide to building control in Northern Ireland explains the process, the notices and why the council is the only route here.

Is it worth it?

Two honest caveats.

You lose the parking and the storage. On a Belfast street where parking is contested, that is a real cost that does not appear in any table. And every garage in Northern Ireland is also a bike store, a freezer room and a place to put the lawnmower. Have a plan for all of it before the plasterer arrives.

It rarely adds as much value as it costs on paper — but it usually adds more usable space per pound than anything else. As a home office, a downstairs bedroom, a utility room or a playroom, £12,000 for 15m² is £800 per square metre. The same 15m² as a new extension in Belfast is £2,000 to £2,600 per square metre all-in. Even a loft conversion at £1,600 per square metre is double the price.

If you have a garage and you need a room, convert the garage. Price your own with the garage conversion cost calculator, then get three quotes against the same written specification.

Figures reviewed August 2026. Indicative estimates for Belfast, VAT included.