jamb
Either of the vertical components that form the side of an opening in a wall, such as that of a door frame, window frame, or fireplace.
jamb: the vertical frame piece that bears the door weight
A jamb is the vertical member on either side of a door, window, or fireplace opening that supports the header and carries structural load. In a typical door frame, you have two jambs (left and right) that hold the hinges or pivot hardware and resist the lateral forces from the door swing. The jambs are typically made from solid wood, engineered lumber, or steel depending on the building type and load requirements.
Door jambs in residential construction are usually 1.375 inches thick (a nominal 1.5-inch board), while commercial steel jambs range from 16 to 20 gauge depending on the opening width and traffic load. The jamb must be plumb (truly vertical) during installation or doors will bind and latches will not strike properly. Most jambs have a rabbet or stop routed along their inner edge to hold the door or window sash against closure.
Jamb failure and adjustment
The most common problem is racking, where settlement or structural movement pushes the top or bottom of the opening out of square. When this happens, doors begin to drag on the floor or catch at the top, and hinges carry shear stress they were not designed for. Shimming behind the hinges or adjusting strike plates provides only temporary relief if the jamb itself is out of plumb.
In masonry or concrete construction, jambs may be formed steel channels or angles that are set during pour, or they may be fastened to the finished opening. Exterior door jambs must be sealed against weather; the junction between jamb, threshold, and sill is a critical detail for water management. Interior jambs in wet areas (kitchens, bathrooms) are often made from plastic-clad or vinyl-wrapped jamb stock to resist moisture absorption and rot.
The term jamb comes from Old French, related to jambe (leg), because the jamb stands as a leg on either side of the opening. In timber framing and masonry alike, the quality of jamb installation directly affects how well a door or window performs. Precise measurement and plumbing during frame installation is far cheaper than repair work after drywall, paint, and hardware are in place.