The short answer
No, but most ordinary pitched roofs can. A roof window needs a pitch within the maker's range, enough clear room between rafters or a structure that can be trimmed, a covering that can be cut and flashed, and a room beneath that benefits from the light. Flat roofs take rooflights, not roof windows. Thatch, heavy stone slate and some metal roofs need specialist treatment, and listed buildings and flats have extra rules.
Pitch comes first
Every roof window is designed for a range of pitches, and the maker publishes a minimum and a maximum. On a shallow roof, water drains slowly and can be driven back under the flashing, so below the minimum a standard window will leak. At the other extreme, a very steep roof can make the window awkward to operate. Most houses fall well within the range, but low-pitched roofs on 1960s and 1970s estates, porches and some extensions may be marginal. How low is too low is worked through in our pitch answer.
If the roof is too shallow for a roof window, a low-pitch flashing system or a flat rooflight may be the solution. We measure the pitch on site with a level rather than estimating it.
Structure and space
The next question is the timber. Rafters run in rows, often a few hundred millimetres apart, and a window that fits between two of them needs little structural change. A wider one needs a rafter cut and a trimmer, as in the page on moving or enlarging a roof window. Roofs built with engineered trusses, common after the 1970s, are a special case. The web members and joints in a truss carry loads in a set pattern, and cutting one can weaken the whole roof. Trussed roofs usually need an engineer's advice before a window is cut in.
Purlins, ridge beams, chimneys and valleys also get in the way. A window set too near a chimney or hip may be impractical. In a loft room, the sill should sit at a height that lets someone see out, which means thinking about the floor level and ceiling slope together.
The roof covering
Roof windows suit tile and slate best, with a flashing kit designed for the profile. Plain tiles, interlocking concrete tiles and natural slate each need a matching kit. Our answer on fitting a roof window in a slate roof covers that case. Other coverings need more thought. Standing seam metal, profiled sheets and shingle-style coverings can take windows, but with different flashing details. Thatch needs a specialist and a different detail altogether. Heavy stone slate on a period house is fragile and expensive to cut and relay.
Flat roofs
A flat or very low roof does not take a roof window, which needs a slope to shed water. The answer there is a rooflight: a fixed or opening unit on a raised kerb, sometimes with a glass dome, lantern or flat glass panel. The choices are explained in the guide to flat roof rooflights. Where the choice is between a lantern and a flat rooflight, see the answer on roof lantern or flat rooflight.
Rules that apply to the house
Even where a roof can take a window, the house may have restrictions. Flats, listed buildings, conservation areas and Article 4 areas limit what can be done without consent, and a loft room needs escape and thermal compliance. We cover the details in the guides on roof windows and building regulations and planning, and your council can confirm for your address. New roof windows are notifiable under the Building Regulations in any case.
The room beneath matters
A roof window is only worth fitting if it improves the room below. A cupboard or a landing with no floor space beneath the opening can take a sun tunnel instead, which brings light down a tube. A loft that is only used for storage may not justify the cost of a window at all. In a habitable loft, think about where the bed, the desk and the stairs go before choosing the window position, because the roof slope limits where a person can stand and the sill must be reachable. Our answer on roof windows for loft conversions covers escape, size and placement.
Existing insulation, wiring and pipework run through the roof space too. A cable or a water pipe in the path of the opening can be rerouted, and a tank or flue near the position can rule it out. These are found on the loft inspection, not from the ground.
What we check on a survey
We measure the pitch, look at the rafters or trusses from the loft, identify the covering and any chimney or valley nearby, and consider the view and light in the room beneath. We photograph the roof and the structure so you can see why a position works or does not. If a roof window will not suit, we suggest the nearest alternative, such as a rooflight or a sun tunnel. The price we give you afterwards is fixed and in writing.
For the full range of work, see our roof windows and skylights page.
Every roof is different. A free survey with photos settles it for yours.
Get a free survey