Garage rooflights
Can you add rooflights to a garage roof?
The short answer
Yes, most garage roofs can take rooflights, and a flat roof or a low-pitched one usually takes them more easily than a tiled roof. The type matters. A glazed unit on a kerb suits a flat deck, while a pitched garage takes a roof window set flush into the slope. If the garage becomes a habitable room, thermal limits and Building Regulations apply.
Which kind of rooflight suits a garage, what has to happen to the roof around it, and the checks to make before cutting a hole.
Two kinds of opening, two kinds of garage roof
Part L of the Building Regulations separates two products. A rooflight is raised on a little upstand of its own. A roof window is fitted level with the slope. For a garage, that means a flat roof takes a rooflight on a raised kerb, and a pitched roof takes a roof window set between the rafters, much as a house would.
A flat-roof rooflight can be a fixed pane, an opening one, or a pyramid or lantern shape. Pitched garages use a smaller standard-sized window, flashed into the tiles or sheets. Our page on flat roof skylights compares the shapes. Before choosing, work out what the opening is for: daylight over a workbench, fresh air for a hobby room, or a brighter store. The answer narrows the choice quickly. The wider garage roof replacement page shows where a rooflight fits into a larger re-roofing job.
What changes in the roof around the new opening
Cutting a hole in a garage roof is never just a hole. The opening interrupts the rafters or joists, and the load they carried has to go round it. On a timber deck we frame the opening with trimmers, which are short timbers fixed between the main members, and a kerb is built up from that frame. On a sheet roof, the corrugated profile has to be cut and the cut edge sealed so water cannot track along the ribs.
On a pitched roof, the roof window needs a flashing kit that fits the covering you have. Rain needs a clear channel past the frame, and a rushed flashing is a classic cause of leaks around windows. On a felt or membrane roof, the upturn at the kerb is lapped and sealed so water sheds over the top. When the covering is already tired, the sensible moment to fit a rooflight is during the re-roof, so the new joints and the new covering belong to one piece of work and one set of dry weather days.
Thermal limits and Building Regulations
For a heated, lived-in room, Approved Document L (2021) Table 4.2 sets two ceilings: 2.2 W/m²K applies to a rooflight, while a roof window must meet either 1.4 W/m²K or a rating in Window Energy Rating Band B. The 2026 edition takes effect on 24 March 2027 and repeats those values in Table 3.2. An upstand built on site should reach 0.35 W/m²K. A building control officer will look for these figures if the garage is being converted, so the supplier's data sheet should state them.
A plain, unheated garage is a different question. Which Building Regulations apply depends on its size, its use and whether it is attached to the house. Ask your registered building control approver, or the council's building control team, before ordering anything. Our page on garage roof Building Regulations sets out the questions to ask. If your job turns out to be notifiable, the paperwork is something we take on for you.
Planning, glass and fragile surfaces
Planning rules for rooflights depend on the type of building and its setting, and the rules for a house roof are not automatically the rules for a garage. A garage in a conservation area, in the National Park or within the grounds of a listed property deserves a question to the planning team at your local council before you commit to an order. Our page on garage roof planning lays out what to ask. Getting an answer in writing costs nothing and saves arguments later with a neighbour or a buyer's solicitor.
Safety matters too. HSE lists rooflights among fragile roof surfaces, and a new glazed unit is fragile until the surround is finished. Nobody should step on a plastic or glass panel, and nobody should stand on old cement sheets either. We work from boards and guard the opening while it is open. For the glass itself, ask for toughened or laminated glazing on the underside, since a hit from a ball or a ladder is far more likely in a garage than in a living room.
Condensation, heat and the real cost
A cold garage with a new glazed opening can drip. Warm, damp air from a car or a drying line meets cold glass and condenses on it. A rooflight with a well-sealed frame and a thermally broken edge shrugs that off better, but the cure for dampness is ventilation as much as glazing. Our page on garage roof condensation goes through the cause and the fix.
The cost depends on the type of unit, the roof it goes into and the work to frame and flash it. A pitched tile roof, a felt flat roof and a sheet roof are three different jobs, so a number only means something after a survey of your garage. Our written quote then gives a single figure for the whole piece of work, covering the lining made good on the inside and the waste taken away. When you read any quote for this job, look for VAT and any access equipment in the total, because a tall garage can need a platform or tower.
Related questions
Garage rooflight questions
Is a rooflight the same as a roof window?
Not in the regulations. A roof window lies level with a pitched slope, while a rooflight is built up on its own kerb. Approved Document L gives each its own thermal limit, which is why a supplier will ask which one you want.
Can I fit one myself and have the roof finished afterwards?
It is better to treat the opening and the roof covering as one job. The flashing has to be built into the covering, and a window installed first often has to be lifted again. We can fit the unit as part of re-roofing the garage, or as a stand-alone job on a sound roof.