A frame stile is the vertical structural member of a door or window frame, running from top to bottom on either side of the opening. It forms the upright portion of the frame assembly and carries the weight of the head (top piece) while anchoring the frame to the surrounding wall structure.
In Dutch construction terminology, the word “boom” is used to describe this element. Interestingly, the same Dutch term also refers to a crane boom or jib — the long arm of a construction crane used for lifting materials. Context determines which meaning applies.
Application
Frame stiles serve several critical functions in building construction:
- Structural support: They bear the vertical load transferred from the frame head and distribute it to the threshold or substructure below.
- Hinge attachment: On a door frame, the hanging stile is the vertical member to which hinges are fixed, supporting the weight of the door leaf.
- Lock housing: The striking stile (opposite the hinge side) houses the strike plate and latch mechanism for the door lock.
- Weatherproofing: In window frames, stiles provide mounting points for seals and weather strips that prevent water and air infiltration.
- Dimensional stability: Made from kiln-dried hardwood or engineered timber, stiles resist warping and twisting over time.
Frame stiles are typically mortise-and-tenon jointed into the head and sill of the frame. In modern construction, they may also be connected using mechanical fasteners or finger joints in engineered timber profiles. The cross-sectional dimensions of a stile depend on the size and weight of the door or window it supports, with standard interior door frame stiles measuring approximately 30 x 90 mm in cross-section.
Related terms
- Frame head
- Threshold
- Mullion
- Transom
- Jamb
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