jamb

Jamb refers to the vertical side member of a doorway or window frame. It defines the opening and provides a mounting surface for hardware such as hinges, locks, and trim. Most doors are framed by two jambs—one on each side—along with a head (top) and a sill or threshold at the bottom. The jambs help preserve the opening’s dimensions and support the weight of the door and its hardware.

Etymology and usage: The term jamb derives from Old French jambe, meaning leg, reflecting the post-like role of the vertical frame members. In everyday use, people distinguish between doorjambs and window jambs, though the underlying concept is the same. Jambs can be integrated into wood framing, or formed within masonry openings by setting a wooden or metal frame against brick or stone. In windows, jambs provide the mounting for the sash and the means to seal against weather.

Construction and finish: Jambs are commonly made of wood, but metal or PVC jambs are used in some applications. They are surfaced to accept trim and enable weather sealing. In timber or frame construction, the jamb is often rabbeted to accept the door stop and the edge of the door. In masonry openings, the jambs must align with the rough opening and may be reinforced with backing or metal components to handle loads and hardware.