Definition
A window hinged on one vertical side that swings outward (or inward) like a door, operated by a crank mechanism, offering excellent ventilation and a tight seal when closed.
A casement window is hinged on its left or right side and opens by swinging outward — or in some European designs, inward — operated by a hand crank at the bottom of the frame. When closed, the sash presses firmly against a continuous perimeter seal, making casements among the most airtight window types available.
How Casement Windows Work
The crank turns a worm-gear operator that extends or retracts an arm attached to the bottom of the sash. This mechanism allows the sash to swing open to nearly 90°, providing excellent cross-ventilation — the open sash acts as a scoop that directs breezes into the room. Modern casements include multi-point locking hardware that engages locks at several points around the perimeter for a weather-tight seal.
Casement vs. Double-Hung
- Air infiltration — casements are significantly more airtight (lower air leakage rate)
- Ventilation — casement opens fully; double-hung opens 50% maximum
- Cleaning — casement sash swings out for easy exterior cleaning from inside
- Screen placement — casement screens are on the interior; can be awkward to remove
- Egress — wide casements meet egress code requirements; double-hung sashes sometimes do not
Common Casement Window Problems
- Failed crank operator — the most common repair; gear strip or broken arm. Replacement operators cost $15–$40; easy DIY.
- Stiff or seized crank — lubricate the operator mechanism with silicone spray; avoid petroleum-based lubricants.
- Sash won’t fully close — warped sash or misaligned hinge. Hinge adjustment or replacement solves most cases.
- Failed IGU seal — fogging between panes; requires IGU replacement same as any double-pane window.
- Broken multi-point lock — lock keepers wear out; replacement hardware available from most window manufacturers.
