A nosing batten is the strip fitted beneath the nosing of a stair tread, closing the joint between tread and riser. The same name is used for the batten fixed under the external cill of a timber window, which throws rainwater clear of the wall. Both do the same job: a neat finish at a place that would otherwise stay open.
On a staircase
Beneath the projecting nosing, a joint remains visible between tread and riser. The nosing batten covers it and softens the transition. It is glued to the underside of the nosing and pinned, usually with a small moulding or rounded arris. A loose nosing batten is a classic cause of rattling on a timber stair: glue and pin it back and the noise goes.
On a window
Under the external cill of a timber window there is often a nosing batten, preferably in hardwood. It projects at least about 5 mm beyond the edge of the cill so that rainwater drips clear instead of tracking back underneath.
Here lies a detail that regularly goes wrong: the gap under the nosing batten must stay open. If that joint is sealed with mastic or expanding foam — with the best of intentions, against draughts — moist air from the construction can no longer escape. The moisture condenses under the cill, and the result is wet rot in exactly the place you set out to protect.
Points to watch
- Never seal the underside of a nosing batten. A deliberately open joint is not sloppy work; it is ventilation and drainage
- Use hardwood or durably treated timber outside; softwood in this position has a short life
- Give it enough projection. Less than 5 mm and water creeps back along the wall face
- Paint the underside too. The soffit of a nosing batten is the most forgotten and most vulnerable surface of a window
- When you find rot around a cill, check first whether the nosing batten is still there and whether the gap beneath it is clear; otherwise the rot simply returns after the repair
Related terms
- Nosing
- Drip sill
- Window sill upstand
- Stair string housing
- Stair tread
- Hydrophobizing
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