Where is the best place for a roof window?

A south-facing slope gives the brightest, warmest room, and in summer it can give too much. A north slope gives even, cool daylight that suits a studio or an office. East catches the morning, west takes the evening sun, which is when a loft bedroom is hottest. None of these is wrong; they just fit different rooms.

Think about what is outside as well. A neighbour's gable, a tall tree or a chimney stack can shade a slope for much of the day. Stand in the loft at different times and see where the light actually falls before you choose a position. Photos taken during the survey help, and we take them from the roof side as well as the room side, so you can compare the light in each position before any timber is cut.

If overheating worries you, a window on a shaded slope or one fitted with an external blind is easier to live with than a large south-facing pane with nothing to control it. Our guide to fitting a roof window covers what the work involves once a position is agreed.

A roof window sits at an angle, so the same unit gives a different view depending on how high it is in the slope. Too low and you see only the guttering; too high and you look at sky and cannot see out while seated. A common aim is a sill at about waist height, which lets you look out standing and still gives light deep into the room.

Headroom matters just as much. In a loft with a sloping ceiling, a window placed where you must duck beneath it is annoying every day. Mark the floor where you can comfortably stand and aim to place the opening above that usable floor, not over the dead space at the eaves.

Escape and the 4.5 metre rule

If the window is to serve as an emergency exit from a loft room, Approved Document B limits that to windows within 4.5 metres of the ground. The opening needs a minimum area of 0.33 m², at least 450 mm in height and in width, and the bottom of the openable area should be no more than 1100 mm above the floor. That rule can fix the height of the sill before views come into it.

Every roof has rafters, the sloping timbers beneath the covering, and a window larger than the gap between two of them means cutting one or more. When a rafter is cut, the load it carried is moved onto trimmers, short timbers fixed across the opening, and onto the neighbouring rafters. That is perfectly normal work, but it costs more than fitting a window into an existing bay.

So position matters for cost. A window sized to the bay between rafters needs only a header and a sill trimmer. One that straddles a rafter needs the timber cut and supported, and a very wide opening may call for a structural engineer's calculation. Our survey measures the rafters from inside the loft and notes whether the roof is cut or trussed. If a trussed roof is involved, the webbing and bracing are not cut without checking, and we explain the options on the quote. Our guide to roof window sizes shows how the standard widths relate to common rafter spacings.

Roof windows face up and out, so overlooking is less of a problem than with a wall window, but it is not zero. A window in a rear slope facing a neighbour's bedroom is worth a second thought, as is a front slope that looks onto a street. If the window is angled low, the person standing inside can see into other gardens and rooms.

One planning rule affects placement directly. Class C.2 of the GPDO covers any slope forming a side elevation of the house. Frosted or patterned obscure glass is required on such a slope whatever height you choose, while the sash itself may only open where its openable parts sit higher than 1.7 metres above the room floor; below that it stays fixed. A window on the side slope of a hipped or end-of-terrace roof therefore needs a decision: move it to the rear slope, or accept obscure glass and either a fixed pane or an opening part set more than 1.7 metres above the floor. Our answer on alternatives to a skylight covers options if neither slope suits.

Our visit covers the roof outside and the loft inside, and we compare the two. We record the covering, the angle of the slope, the rafter centres, the position of any chimney, water tank or ductwork, and where the ceiling line falls. A window placed too close to a chimney needs extra flashing and sometimes a lead gutter; one placed under a valley is hard to make watertight.

MyBuilder's 2026 roof window guide puts installation at £350 to £600 for standard jobs, with scaffold at about £500, which is national typical pricing, not ours. The written quote we send after the survey covers the window, scaffold, structural timbers and making good, and the photographs we take explain why one position costs more than another.

Our skylight and roof window page gives the wider picture, and the work carries a 10-year workmanship guarantee in writing.