What is a trapezoid window?
A trapezoid window is a window in the shape of a trapezoid (UK: trapezium): a four-sided figure with two parallel sides. The other two sides are not parallel. In practice, a window with two right angles and one sloping edge is also called a trapezoid window. It belongs to the family of shaped or special-shape windows.
Where you find it
- Gable ends: under a pitched roof the top of the window follows the roof slope, so the glazing can run right up to the ridge.
- Lofts and galleries: in the gable or under the roof slope, for extra daylight.
- Modern architecture: as a deliberate design feature in a facade with sloping lines.
- Historic: trapezoid openings are very old. Well-known examples are the trapezoidal niches, doorways and gates in Inca buildings in Peru, where the opening narrows towards the top.
Points to watch
- Fixed or opening: shaped windows are often fixed lights. An opening sash in a trapezoid shape is more complex and expensive, so a rectangular opening window is often placed below a fixed trapezoid section.
- Bespoke glass: the glazing is made to an exact template. Measure carefully (every side plus the slope or angle) or let the supplier survey.
- Blinds and curtains: standard roller blinds do not fit a sloping edge. Made-to-measure pleated or shaped blinds exist but cost more.
- Weathertightness: the sloping head sits right under the verge. Pay attention to flashings, membranes and the verge detail to avoid leaks.
- Permission: a new or larger window in a front elevation or a listed building may need planning permission. Check with your local authority first.
Related terms
- Gable end
- Oculus
- Diocletian window
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