What is a French casement window (stolpraam)?
A French casement window is a pair of side-hung sashes in a single frame with no fixed mullion between them: one sash closes against the other. It works like a French door in window form. In Dutch joinery this is called a stolpraam, and the door version a stolpdeur. The joint between the sashes is usually covered by a bead on one sash, known in Dutch as a stolpnaald, that fits a matching rebate in the other.
With both sashes open you get one wide, unobstructed opening, useful for ventilation and for passing large items through. The trade-off is that the sashes do not work independently. One is the primary sash and the other the secondary: the secondary is fastened first, typically with bolts or an espagnolette engaging the head and sill, and the primary closes over it. Some modern versions use a “flying” mullion fixed to one sash instead, which still swings clear when opened.
Recognising it
Close the window and look at the centre. Ordinary paired casements close against a fixed post. A French casement shows only a narrow strip over the joint. A Dutch stolpdeur often has no handle outside, because it can only be opened from within.
Application
- Open in the right order. Open the primary sash first. Forcing the secondary sash can split the bead or strain the hardware.
- Plan for small-scale ventilation. Opening a whole sash just to air a room is not always practical; a top light or vent above helps.
- Pay attention to security. The meeting joint is a weak point. When replacing, ask for multipoint locking such as espagnolettes engaging the frame on both sashes.
- Keep old ones working. Old timber pairs often bind because of built-up paint in the joint. Sand back paint rather than planing away timber.
- Respect historic façades. On older Dutch and other European buildings this type is often original; replacing it with mullioned windows changes the elevation.
Common mistake: expecting a French casement to behave like two separate windows. The sashes depend on each other, so the opening sequence matters.
Related terms
- Meeting stile bead
- Casement window
- Espagnolette
- French-door mullion
- Double door
- Rebate
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