The short answer
Most garage roofs can take a rooflight, but the way it is fitted depends on the covering. A flat roof takes a kerbed rooflight or a flat glass unit, a tiled pitch takes a roof window, and a sheet roof takes a translucent panel. Part L sets a limit of 2.2 W/m²K for rooflights, and a cement-sheet roof must never be cut without proper advice.
Three kinds of garage roof, three kinds of rooflight
A flat garage roof takes what the trade calls a rooflight: a pane of glass or polycarbonate set in a kerb, an upstand of timber that lifts the unit above the waterproof covering. The covering is dressed up the kerb, so the water has no reason to enter at the joint. Some units are fixed, others open for ventilation, and flat glass types sit almost level with the surface.
A pitched garage with tiles or slates takes a roof window, set into the slope like those on a loft. The window sits between rafters, with a flashing kit around it so the tiles meet the frame neatly. Our page on pitched garage roofs explains how those roofs are built, which helps you judge how much of the structure has to move.
A profiled sheet roof, whether steel or fibre cement, can take translucent sheets of the same profile in place of one or two normal sheets. These let in diffused light and cost little to fit, but they are a sheet-for-sheet swap and the neighbouring sheets have to be sound.
The cement-sheet warning
This is the point where a simple job can go wrong. If your garage roof is made of corrugated cement sheets, it may contain asbestos. HSE's guidance for anything built or refurbished before 2000 is to presume asbestos until a test shows otherwise. Cutting, drilling or breaking a cement sheet to make an opening releases fibres and is not a task for a ladder and a jigsaw.
Under HSE guidance, lifting cement sheets off whole is non-licensed work, but once they are badly broken the job becomes notifiable. So the correct route for a cement-sheet garage is usually to test, then remove whole sheets with care and fit new ones, or replace the roof. We do not cut a rooflight into an unidentified cement sheet.
If you are weighing up a sale, the same issue comes up with a buyer's survey, and our page on selling a house with an asbestos garage roof covers what buyers ask. A roof that is already compromised is a poor place for a new opening.
Light, heat and what the regulations ask
Where a garage is used only for storage, a rooflight is a convenience. Where it is a workshop, gym or studio, thermal performance and overheating start to matter. Approved Document L, 2021 edition incorporating 2023 amendments, sets limits for new or replacement elements in existing dwellings. Roof windows are held to 1.4 W/m²K, with Band B on the Window Energy Rating scale accepted instead. Rooflights are held to 2.2 W/m²K. Where a kerb or upstand is built on site, it should have a maximum U-value of 0.35 W/m²K.
These figures apply to dwellings, and whether a particular garage counts depends on how it is attached and used. Do not guess. Ask your building control body, which may be Swindon Borough Council's own team, and for planning questions, check with Swindon Borough Council's planning team. Turning a garage into a living room is a different project, and our page on garage conversion roofs explains what changes for the roof.
South-facing glass in a small flat-roofed space can make the room hot in summer. A tinted or solar-control pane or an opening vent reduces that, and a rooflight above a workbench is often better placed on the north side.
What fitting a garage rooflight costs
National guides give a feel for the numbers rather than a quote. MyBuilder's roof window guide, updated 21 August 2026, puts installation at £350 to £600 for an ordinary job, with the fitter's time included, with a standard centre-pivot window at £305 and an electric one £420 to £590. It adds around £500 for scaffolding where access needs it. Those figures are for roof windows in a pitched roof, not flat rooflights or sheet panels.
What moves the price on a garage is mostly the roof. A flat roof usually needs the covering opened up, a kerb built and the whole area re-dressed, so a rooflight is often best fitted when the covering is being renewed. A tiled slope needs tiles lifted and a flashing kit, and a sheet roof needs the correct replacement panel and fixings.
The window itself is one cost; the structure, finish inside and any electrics are the others. We give one written total after the survey, so before you compare prices, find out if scaffold and VAT sit inside each total.
Getting it right, and where else rooflights help
Most problems come from the joint, not the glass. A rooflight fitted into an old felt roof with a smear of mastic will often leak within a season or two, because the covering below is on borrowed time. The best moment to fit one is with a new covering, when the kerb, deck and membrane can be built together. Our note on garage guttering covers the other part of the water path, since a rooflight with no way to shed rain neatly makes a mess at the wall below.
The same idea applies to open structures. A polycarbonate sheet over a carport lets light through to the car and the path, but it only lasts about 10 to 15 years in conservatory use and fades or yellows over time. Our carport roof page sets out the choices.
If you want a rooflight in your garage, start with the survey. We examine the covering and the deck, decide whether cutting is safe, and send survey photographs from your garage with one written quote. See our garage roof replacement page for how that works.