A roof window is a glazed unit designed to sit within the plane of a pitched roof covering, weathered by a flashing kit made to suit that covering’s profile. It opens in most cases, it relies on the pitch of the roof to shed water past it, and it is not the same product as a flat roof rooflight.
What makes it a roof window
Two things: it sits in the covering, and it is weathered by a kit rather than an upstand.
The frame is set so the covering laps over its flanges at the head and sides and under it at the foot, with soakers interleaved between the tiles or slates.
The pitch of the roof does the rest, carrying water down and around it.
The parts of one
A frame, a sash carrying the glazing, and the flashing kit around it.
The frame is fixed to the rafters or to timbers trimmed between them. The sash opens within it. The kit is a separate order and it is what keeps water out.
How it opens
Centre pivot or top hung, and the choice affects the room more than the roof.
A centre pivot sash rotates about the middle of the frame, which is simple and reverses for cleaning. A top hung sash swings outward from the top, which gives a clear opening and an uninterrupted view.
Which suits a room depends on where somebody stands and how high the window sits.
Fixed versions
Available, cheaper, and appropriate where ventilation is not wanted.
A fixed unit has no sash, no ironmongery and nothing to maintain, and it cannot serve as an escape window or provide purge ventilation.
What it is made of
A timber or a plastic clad timber frame in most domestic ranges, with an aluminium or plastic external cladding.
The timber is the structure and the cladding is the weathering. Fully plastic frames exist and suit bathrooms and other humid rooms.
Against a conservation rooflight
A different family for a different purpose.
A conservation unit is slimmer, sits lower in the covering, is dark and generally carries a bar, and it is what a designated slope wants.
A standard roof window is bulkier, projects more, and is what almost every undesignated roof has.
Against a flat roof rooflight
Not interchangeable, and the distinction matters.
A flat roof unit sits on a kerb above a deck. A roof window sits in a pitched covering. Putting one where the other belongs fails.
The comparison is on the difference between a roof window and a rooflight.
The flashing kit
The component that does the weatherproofing, and it is chosen by the covering rather than the window.
Flat coverings take one kit, profiled tiles another, and the wrong one leaves a void under every roll.
What it is is on what is a flashing kit.
Minimum and maximum pitch
Both exist, and the minimum rules more jobs out than the maximum.
Below a stated pitch the manufacturer will not warrant the unit, because water does not clear it reliably.
The figures are on the minimum pitch for a roof window.
What structure it needs
An opening trimmed between rafters, sized to the unit.
On a cut roof a rafter can be trimmed with a designed detail. On a trussed roof the members are not cut and the unit fits between them.
What that allows is on can a roof window be fitted between trusses.
How much light it gives
Considerably more than a wall window of the same area.
Glazing facing the sky sees the whole hemisphere rather than a slice of it, so a modest roof window transforms a room a larger window would only improve.
The comparison is on how much light does a roof window give.
Escape windows
A specific duty some roof windows are designed to perform.
Where a loft room is a habitable bedroom, one window may have to serve as means of escape, with a clear opening dimension and a sill height set by regulation.
Which units satisfy it is on can a roof window be an escape window.
Blinds and accessories
Made to fit the frame rather than bought generically.
Manufacturer blinds run in channels designed into the frame, which makes them neat and specific to that unit. A generic blind rarely sits as well and can foul the sash.
Manual and electric
Both available, and the cable is the decision.
A powered unit needs a supply at the opening, which is minutes while a ceiling is open and a separate job afterwards. Solar powered versions avoid the cable entirely.
Where they go
Almost anywhere with a pitched roof over the room.
Loft conversions, rooms already in a roof, stairwells, landings and bathrooms. A stairwell is the position that does most work, because light falls the full height of the stair.
What decides whether one can be fitted
Four things, in order.
Whether the room has a pitched roof over it. Whether the pitch is within range. What the structure is. And whether the covering has a kit made for it.
How long they last
Decades on a well installed unit, and the components age at different rates.
The frame and the cladding outlast everything. The sealed unit has a finite life and can generally be replaced in a sound frame. Ironmongery wears and is a serviceable part.
Which means a roof window is rarely replaced whole because one thing has failed.
Maintenance
Modest, and it is mostly cleaning.
Glass when it is dirty, the seal kept clean so it compresses evenly, and hinges and stays checked occasionally. A centre pivot sash reverses so the outside can be cleaned from within the room.
What we settle first on a pitched roof
We establish the covering, the pitch and the structure before choosing a product, because those three decide which units are actually available on a given roof.
The whole picture is on the roof window installation page.
Thinking about this job? We survey across Worthing, West Sussex and the South Downs and give you a fixed price before any work starts, with a 10-year workmanship guarantee.