A jamb is the side surface of a wall opening — the inside face of the masonry or wall that becomes visible when you look at a window, door or shutter from the side. The jamb runs from the outer face of the facade to the frame and determines the depth and finish of the opening.
Jamb, reveal and rebate
| Term | Description |
|---|---|
| **Jamb** | The full side surface of the wall opening |
| **Reveal** | The narrow strip between the frame and the wall edge (part of the jamb) |
| **Rebate** | The recess in the frame into which the window or door sits |
Why is the jamb important?
- Insulation — an unfinished jamb is a cold bridge; PU foam or insulation board prevents heat loss
- Sealing — the junction between jamb and frame must be wind and watertight
- Aesthetics — a neatly finished jamb gives a professional result
Finishing a jamb — options
| Material | Application | Suitable for |
|---|---|---|
| **Plaster / render** | Traditional, smooth surface | Existing buildings, masonry |
| **Plasterboard** | Quick interior finish | Timber frame, renovation |
| **HPL / plastic board** | Low maintenance, moisture resistant | External jamb, bathroom |
| **Timber jamb lining** | Classic appearance | Listed buildings, timber frames |
Insulating the jamb during frame replacement
- Remove the old frame and clean the jamb
- Apply PU foam or insulation strip along the jamb
- Install the new frame level and plumb
- Fill the remaining space with PU foam
- Finish the jamb with plaster, board or a trim profile
Related terms
- Frame
- Reveal
- Rebate dimension
- Sill
- Tolerance dimension
- Blind window