What is fitting clearance?
Fitting clearance (stelmaat) is the gap between a window or door frame and the wall (the reveal) needed to align the frame plumb and level. This gap is filled with PU foam after alignment and sealed with caulk on the outside. Without fitting clearance, you cannot align a frame in a wall that is not perfectly straight.
How much fitting clearance?
The standard fitting clearance is 5-10 mm per side. This means the frame is 5-10 mm smaller on all sides than the structural opening.
| Situation | Fitting clearance |
|---|---|
| New build (neat brickwork) | 5-7 mm |
| Renovation (older walls) | 7-10 mm |
| Timber frame construction | 5 mm |
Fitting a frame
- Place the frame in the opening — On plastic packing shims
- Check level — Horizontally and vertically
- Check plumb — With a spirit level against the jambs
- Adjust with shims and wedges — Until the frame is perfectly positioned
- Secure — With frame screws or plugs
- PU foam — Fill the clearance gap (not too much, foam expands)
- Seal — Caulk the outside for weather tightness
Related terms
- Structural opening
- Rebate size
- Frame