A roof window is a window installed in the sloping plane of a pitched roof, intended to add daylight, fresh air and sometimes a view to the loft or top floor of a house. Unlike a dormer window, a roof window follows the pitch of the roof without forming its own structure above the roof line.
Components of a roof window
A modern roof window consists of:
- Fixed frame — a timber or plastic frame fitted between the rafters
- Operable sash — usually fitted with double or triple low-E insulating glass
- Flashing kit — a prefabricated assembly that creates a watertight connection to the roof covering
- Operation — at the top or bottom, manual or electric with a rain sensor
Types of roof windows
- Centre-pivot window — pivots around a horizontal axis in the middle, suitable for lower sill heights
- Top-hung window — opens fully outward, with hinges at the top and unobstructed view
- Combination window — combines both pivot and top-hung operation
- Egress / access roof window — opens fully and can serve as an emergency exit
- Roof window band — multiple roof windows coupled side by side or vertically
Installation and connection
A roof window is fitted between two rafters; if the window is wider than the rafter spacing, a trimmer assembly is created. The connection to the roof surface is made with a flashing kit that catches water from above and channels it to either side. With tiles, the flashing apron is dressed around the tiles; with slate or bitumen a special flashing is used.
Application
A roof window is a light and relatively inexpensive way to make a loft or top floor habitable. It provides more daylight per square metre than a dormer but less head height and less view. Building regulations require minimum daylight and ventilation areas per habitable room; separate rules apply if the window is to act as an emergency egress.
Related terms
- Dormer window
- Skylight
- Roof light
- Rafter
- Roof sheathing
Want to learn more about construction terms? Visit our knowledge base at fredsdiyplans.com.