A flap window is a window that pivots on a horizontal axis and swings open as a whole. Unlike a casement (vertical axis) or a pivot window (axis through the middle), the hinge line here runs along the top or the bottom of the sash. The Dutch term is klapraam.
There are two main forms:
| Form | Hinge line | Opens |
|---|---|---|
| Awning / top-hung | Top | Outward |
| Bottom-hung falling sash | Bottom | Inward |
It is worth distinguishing this from a tilt window, which is bottom-hung and tilts inward at a narrow gap only, while a falling sash swings inward as a whole leaf.
Where it is used
- Fanlights and ventilation lights — a flap window over a door or a fixed light is a classic ventilation arrangement
- Ventilating in the rain — an outward-opening awning sash acts like a canopy: the opening sits under the sash, so rain is less likely to blow in
- Basement and loft windows — an inward-falling sash takes little space and lets air in over the top
- Historic buildings — flap windows are common in older frames, often with a casement stay with set positions
Points to watch
- Limit the opening mechanism — the sash has to be secured when open with a stay or scissor hinge; wind with a free run will bend the ironmongery or pull the sash out of the frame
- Water shedding on an inward-falling sash — an inward-opening leaf needs a sound junction with the bottom sill; the drip sill, the rebate and the seals matter here
- Fall protection — a low-set inward-opening sash needs the fall protection resolved; check the requirements that apply to the situation
- Escape route — a flap window is usually not suitable as an escape opening: the clear opening is limited and the sash is in the way
- Maintenance — grease the hinge and the stay outside regularly; on timber sashes keep the top edge well painted, as that is where water stands
Related terms
- Tilt window
- Tilt and turn window
- Rooflight
- Window frame
- Bottom sill
- Window restrictor
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