Loft Conversion Costs in Northern Ireland - 2026 Price Guide

A loft conversion is usually the cheapest way to add a proper bedroom to a Northern Ireland house, because you are buying a floor, some insulation and a staircase rather than foundations, walls and a roof. It is also the project most likely to be quoted by someone who has not been in the roof space, which is how people end up with a price that doubles in week three.

Here is what it costs here in 2026, and what decides whether your particular roof is a straightforward job or an expensive one.

The 2026 range: £25,500 to £63,750

For Belfast and the wider Northern Ireland market, a loft conversion runs £25,500 to £63,750 all-in, including professional fees and contingency. Northern Ireland sits roughly 15 per cent below the UK average for this kind of work, and almost all of that difference is labour.

That is a wide band because "loft conversion" covers four quite different jobs. Break it down by type and the numbers get useful.

What each type costs

Rooflight conversion

The cheapest and least disruptive. The roof structure stays as it is, you get a floor, insulation, a staircase, plasterboard and two or three rooflights. It only works if the existing roof already has the height and the pitch — no amount of money makes a shallow 1980s roof usable without changing its shape.

Rear dormer

The default for most Northern Ireland semis and terraces. A flat-roofed box off the rear slope turns a triangular attic into a room with walls. Ugly from the back garden if it is done badly, invisible from the street if it is done well. This is where most people land.

Hip to gable

If your house has a hipped end — the sloped end wall you see on countless 1950s and 1960s semis around Belfast — squaring it off to a vertical gable adds a surprising amount of floor area. It usually gets paired with a rear dormer, and it means proper scaffolding, a rebuilt end wall and matching the existing render or brick.

Mansard

Rare on domestic work here, mostly seen on older terraces and where planning constraints push the design that way. It is effectively a new roof, and it is priced like one.

Will your loft convert at all?

Three things decide it, and you can check two of them yourself this afternoon.

Head height

Stand under the ridge and measure to the top of the existing ceiling joists. As a working rule you want 2.4 metres or more before any work starts. The finished floor will come up 150 to 250mm once new joists or steels and insulation go in, and the ceiling will drop where insulation goes between the rafters.

The building regulations do not set a minimum ceiling height for a loft room in the way people imagine, but they do require headroom over the staircase, and a room you cannot stand up in is not a room anyone wants. If you measure under 2.2 metres, you are looking at a dormer or a mansard, not a rooflight conversion.

The roof structure

This is the big one in Northern Ireland, because so much of our housing stock is post-1965.

• Cut roofs — individually cut rafters and purlins, typical of pre-1960s houses, the Victorian and Edwardian terraces of south and east Belfast, and older rural properties. The middle of the loft is usually open and the conversion is comparatively straightforward.
• Trussed rafters — the W-shaped prefabricated trusses used on almost everything built from the mid 1960s onwards. The web of timbers filling the loft is structural. You cannot simply cut it out. The conversion needs steel beams to pick up the roof and the new floor, and that typically adds £3,000 to £7,000 to the job before you have gained a square metre.

If you can walk from one end of your loft to the other, you probably have a cut roof. If you have to climb through a lattice of timbers, you have trusses.

Where the stairs go

The staircase is the constraint that sinks more loft conversions than head height does. It has to land somewhere sensible on the floor below, with proper headroom over it, without eating the landing or a bedroom. On narrow terraces the honest answer is sometimes that it cannot be done without losing a room, at which point the sums change completely.

What is in the price

A typical dormer conversion price should cover:

• Structural steels, new floor joists and the floor deck
• Dormer construction, roof covering, cladding and rainwater goods
• Insulation to current standards, plasterboard and skim
• A staircase, balustrade and fire doors to the new escape route
• Rewiring the loft, lighting, sockets, smoke and heat alarms
• Radiators and pipework extended from the existing system
• Two or three rooflights, decoration and floor covering

What usually is not

That last one is worth thinking about. If the roof is 40 years old, the marginal cost of recovering it while the scaffolding is already there is much less than doing it as a separate job in five years.

Building control: the part that is not optional

Every loft conversion in Northern Ireland needs building control approval from your district council. There is no private approved inspector route here — the council does it. The rules that shape the design are:

• Fire and escape. Turning a two-storey house into three storeys changes the escape strategy. You will normally need a protected stairway running to a final exit, fire doors to the rooms off it, and mains-powered interlinked alarms. Where a protected route genuinely cannot be formed, other measures — including sprinklers — sometimes come into it. Your building control officer decides which route applies to your house, so involve them early rather than after the design is fixed.
• Structure. Steels, their bearings and the new floor need to be designed. Budget for a structural engineer.
• Insulation and ventilation. The roof becomes a warm element of the building fabric and has to perform. Getting the insulation right also means keeping the ventilation right — a badly detailed warm roof in our damp climate will show you condensation within a winter.

There is more on how the system works, and on commencement and completion notices, in our guide to building control in Northern Ireland.

Do you need planning permission?

Often not. Many loft conversions fall within permitted development, provided the roof addition stays within the volume allowance, does not extend beyond the plane of the roof slope on the elevation fronting a road, and uses materials similar in appearance to the existing house. Terraced houses get a smaller volume allowance than detached and semi-detached ones.

The exceptions matter: conservation areas, areas of townscape character, listed buildings, flats, and any property with an Article 4 direction or a restrictive planning condition. Our guide to planning permission in Northern Ireland covers where permitted development stops and who to ask.

Loft or extension?

Per square metre, a loft conversion is usually the cheaper of the two, because the shell already exists. A 25m² dormer conversion at £40,000 works out around £1,600 per square metre. The same 25m² as a ground-floor extension in Belfast is £2,000 to £2,600 per square metre all-in.

The loft also keeps your garden, which on a small urban plot can be worth more than the money. Against that, the extension gives you living space rather than a bedroom, and it does not cost you a landing.

If neither works, look at a garage conversion — it is the cheapest floor area you will ever add.

Timescale

Six to ten weeks on site for a straightforward dormer, longer for hip-to-gable work where the end wall has to be rebuilt and rendered to match. Add the design and approval period in front of that: drawings, engineer's calculations and the building control application will realistically take another six to eight weeks before anyone is on the roof.

Get a price for your own house

Type your dimensions and postcode into the loft conversion cost calculator for an indicative range priced for your area, with the breakdown behind it. Then take that to three local builders and ask them to price the same specification — our twelve questions for choosing a builder is a useful thing to have in your hand when they arrive.

Figures reviewed August 2026. Indicative estimates for budgeting, not quotes.