Nail sealing tape is a self-adhesive, usually closed-cell foam tape applied to a roofing underlay beneath the counter batten, so that the holes made by nails or screws are sealed again. Without it, every fixing is a puncture in the roof’s second line of defence — and on a single roof slope there are easily several hundred of them.
Why it is needed
Beneath the tiles or slates lies a breather membrane whose job is to carry away any water that gets past the covering. The counter batten is fixed through that membrane, and the tiling battens run across it. Every nail pierces the membrane. On a steep roof this is usually tolerable, but the shallower the pitch, the longer water stands on the membrane and the more readily it wicks down the nail shank. Underlay manufacturers therefore specify nail sealing tape at lower pitches and wherever performance requirements are raised. The tape also stops the membrane flapping against the sharp batten edge and tearing in the wind.
Applications
- Pitched roofs — under every counter batten, from eaves to ridge
- Walls — under the battens of a ventilated cladding fixed over a breather membrane
- Low pitches — wherever the manufacturer sets enhanced requirements
- Dormers and abutments — at the points where water concentrates
Installation
- Apply the tape in one continuous strip exactly where the counter batten will sit
- Choose a width that leaves the tape visible on both sides of the batten; 50 to 60 mm is common for battens of 25 to 38 mm
- Work on a clean, dry, dust-free membrane; the adhesive will not bond to a wet or dirty surface
- Fix the counter batten through the centre of the tape so the foam is compressed around each nail
- Observe the application temperature the manufacturer states; hot-melt adhesives bond poorly in frost
Points to watch
- Nail sealing tape cannot be added afterwards — it has to be in place before the counter battens go on
- It does not replace proper detailing at ridge, eaves, valleys and penetrations
- Check that the tape and the membrane are compatible; not every combination is approved
- Membrane laps are still required; the tape only seals the perforations
Related terms
- Counter batten
- Breather membrane
- Tiling batten
- Underlay
- Sealing tape
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