Can rooflights be fitted to a garage roof?

The condition question first

Garage roofs are often the least maintained part of a property. A covering that was adequate over a car may not be sound enough to cut a new opening into and expect a durable joint.

Part of the survey is deciding whether the roof takes a new opening or wants recovering. On an old felt or GRP roof near the end of its life, the honest answer is often the latter.

If it is being converted

This is the moment. Converting a garage to habitable space triggers Building Regulations, and the roof has to meet the thermal standard for a habitable room. That usually means the roof is being opened and upgraded anyway.

Adding the rooflight then costs a fraction of adding it afterwards, and converting a cold deck to a warm roof at the same time makes the kerb detailing simpler and more robust.

If it stays a garage

Different calculation. There is no thermal requirement, so a simpler and cheaper unit is entirely reasonable. This is one of the few places we would say a polycarbonate dome is a sensible choice: cheap, light, sheds water by shape on a poorly drained roof, and nobody is looking at it.

How many

Garages are long and narrow. One unit in the middle lights the middle; two spaced along the length light the space. Position them clear of the party wall with the house and clear of any valley where the garage roof meets the main roof.

Head height

Worth checking early in a conversion. Garage ceilings are often low, and adding insulation above the deck reduces it further. A splayed reveal around the rooflight gains a little back.

Yes, and it is usually a straightforward job

A garage is one of the easier places to fit a rooflight. It is single storey, so access is a tower rather than scaffold. Making good matters less than in a habitable room. And there is rarely a heritage question unless the garage is part of a listed curtilage.

Whether it is a pitched or flat roof decides the product.

Pitched garage roofs

Usually trussed rafters on anything modern, frequently at 600mm centres, so a unit sized to sit between two trusses needs no structural work at all.

The covering is often profiled concrete tile, which needs a deep flashing kit rather than the flat kit used on slate. Some older garages have corrugated cement sheet, which is a different matter: sheets of that age may contain asbestos and are not disturbed without testing.

Flat garage roofs

Felt or single ply in most cases, and the same rules apply as any flat roof: a kerb of at least 150mm, the deck falling away from it, and the covering dressed up the kerb and terminated properly before the unit sits on it.

Garage flat roofs are frequently older and were laid with minimal fall, so correcting the fall locally around the kerb is more likely here than on a recent extension.

Specification for a garage

Non fragile, which matters more here than almost anywhere. Garage roofs get walked on for gutter clearance and to retrieve things, and old polycarbonate domes are the classic fragile hazard.

Security, because a garage is a target and it is frequently the least overlooked part of a property. A laminated inner pane and mechanical fixing to the kerb are worth specifying.

Ventilation, if the garage is used as a workshop. An opening unit at the highest point clears fumes and moisture far better than a door left ajar.

Thermal performance, which matters less in an unheated garage. Where it is heated or being converted, specify as you would for a habitable room.

Regulations

An unheated detached garage is exempt from most of Part L, so the thermal requirement that applies to a dwelling does not bite in the same way. Structural work still engages Part A.

Where the garage is attached to the house, or is being converted to habitable use, the full requirements apply and it is notifiable.

What the roof usually is

Most domestic garage roofs are either a shallow pitch with a light covering or a flat roof with felt or a single ply membrane, and both are built to a lower structural specification than a house roof because they carry nothing and no one.

That matters for two reasons. The structure may need strengthening around the opening, and the existing covering may be near the end of its life, in which case fitting a rooflight into it is spending money on a roof that is about to be replaced.

Checking the covering condition first is the single most useful thing to do before pricing a garage rooflight.

Where a garage becomes a room

The most common reason for this question is a garage conversion, and that changes the answer considerably.

Once it is habitable space, Building Regulations apply. The roof needs insulating to current standards, which usually means a warm roof build up, and the rooflight has to meet the thermal requirements for a new element.

The condensation risk changes too. An unheated garage does not care about a cold bridge. A converted room does, and the kerb insulation and vapour control detailing that were irrelevant before become essential.

Security, which matters more here

Garages hold tools and bicycles and are frequently unoccupied. A rooflight is a potential access point, and laminated glass rather than toughened is worth specifying, because laminated glass holds together when attacked rather than clearing the opening.