What is a casement window?
A casement window is a window that can be swung open (outward or inward), as opposed to a fixed window that does not move. The moving part of the window is called the sash or leaf, and it is attached to the frame by hinges. Casement windows are used for ventilation and are available in various opening mechanisms.
Types of casement window
| Type | Opening direction | Characteristic |
|---|---|---|
| Side-hung casement | Swings around vertical axis (left or right) | Classic, can be fully opened |
| Top-hung (tilt window) | Tilts inward from the bottom | Safe ventilation, difficult to fall through |
| Tilt-and-turn | Combination of tilting and turning | Flexible — most popular choice |
| Fanlight / transom light | Small upper section that can be opened | Ventilation in combination with fixed lower section |
| Sliding sash | Slides horizontally | Minimal protrusion, modern look |
Tilt-and-turn window — the modern standard
The tilt-and-turn window is the most widely sold window type in Continental Europe:
- Tilt position: window tilts inward at the top around the lower hinge — ventilation without a security risk
- Turn position: window swings fully open — maximum opening and cleaning from inside
- Closed: fully sealed
Frame material
| Material | Advantages | Disadvantages |
|---|---|---|
| uPVC | Affordable, low maintenance, good insulation | Fewer design options, not repairable |
| Timber | Attractive, good insulation, repairable | Regular maintenance required |
| Aluminium | Slim profile, durable, many colours | Poorer thermal insulation (without thermal break) |
| Timber-aluminium | Timber inside, aluminium outside | More expensive, but low maintenance |
Thermal performance
For modern casement windows:
- Minimum standard: double glazing (Ug ≤ 1.1 W/m²K)
- Passive house: triple glazing (Ug ≤ 0.6 W/m²K)
- Always check the Uf-value (frame insulation value) — not just the Ug-value (glass insulation value)
Replacing a casement window — DIY feasibility?
- Replace the sash with the same frame: yes, if the size matches
- Replace the complete window including frame: demanding but achievable
- Enlarge the opening: check or renew the lintel — specialist recommended
Related terms
- Fixed window
- Roof window (skylight)
- Glazing
- Window frame
- Tilt-and-turn hardware
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