Jamb
The vertical sides and head of a door or window frame.
Quick Answer
A jamb is one of the pieces that line a door or window opening: two side jambs and a head jamb, which together form the frame. The door hangs from one side jamb and closes against a stop. Estimators usually count the whole frame as one unit from the door schedule, or take loose jamb stock in linear feet.
The Full Picture
The jamb is the lining of an opening. A door frame has a head jamb across the top and a side jamb on each side, and the door is hinged from one side jamb and closes against a stop. Windows have a head, sill and side jambs. Jamb width is set by the thickness of the wall, so the jamb is sized to the wall assembly rather than the door. In a 2x4 wall with 1/2 in board on each face a common jamb width is 4-9/16 in, though the actual dimension depends on the wall type, and the door schedule or the frame types in the drawings give the requirement.
In most takeoffs the jamb is not measured on its own. A door schedule lists each opening with size, material, frame type, hardware set and fire rating, and a hollow metal or wood frame is counted as one each, with the jamb part of it. Estimators check the frame elevations and the specification section for doors and frames, and keep the frame separate from the door leaf and the hardware. Pre-hung units combine the jamb, door and casing, so check which items the supplier is including to avoid double counting.
When the jamb is loose lumber, as in site-built wood frames or window returns, it is counted in linear feet: two sides plus the head, and a sill for windows. Extension jambs on windows are a separate item that is easy to miss when walls are thicker than standard. Wood jambs for rated doors need to match the rating of the assembly, so confirm the frame type and rating before pricing.
The jamb is also where accessibility is checked. The U.S. Access Board states that the clear width is measured from the stop, with a 32 inch minimum clear width, so the frame and the stop set the usable opening and the estimator should confirm the door width on the schedule.
Real Examples
Common Misconceptions
People assume: The jamb and the casing are the same thing.
Actually: The jamb lines the inside of the opening. The casing is the trim on the face of the wall that covers the gap between the jamb and the wall. They are priced separately.
People assume: Jamb width is the same for every door.
Actually: It follows the wall thickness, including the board on both faces, so different wall types in the same building need different jamb widths.
Does MeltPlan Solve This?
Partially — adjacentJambs and frames are counted from the door and window schedules and the plan sheets, and MeltPlan's takeoff service covers that counting: AI pulls quantities from plans and US-based experienced estimators review and adjust them. Frame types, ratings and what a supplier includes stay with the estimator.
Get door and window frame counts pulled from your plans →Frequently Asked Questions
What is the difference between a door jamb and a door frame?
The jamb is one piece of the frame. The frame is the full assembly of two side jambs and a head jamb, sometimes with a stop and a threshold. People often use the words interchangeably.
How do you count door jambs in a takeoff?
Most estimators count the frame each from the door schedule. When the jamb is loose wood, they take two sides and a head in linear feet and add the width and a cutting allowance.
What is a head jamb?
It is the horizontal piece across the top of the opening, between the side jambs. Windows also have a sill at the bottom.
Does the jamb affect the clear opening of a door?
Yes, through the stop. The U.S. Access Board guide measures clear width from the stop to the face of the door open 90 degrees, so the frame detail and door width control the clear opening.