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Breathable roof membrane underlay at 120GSM is a vapour-permeable felt designed for use beneath tiled or slated pitched roofs. This 1m x 50m roll allows moisture vapour to escape while blocking water ingress, making separate eaves ventilation unnecessary in most applications.
| Material | Polypropylene non-woven fabric |
|---|---|
| Grade | 120GSM |
| Nominal Size | 1m x 50m per roll |
| Coverage | 50 square metres per roll |
| Use Class | Pitched roofs, tiled or slated, warm or cold roof construction |
Lay the membrane horizontally across the rafters with a minimum 150mm overlap at horizontal laps and 100mm at vertical joints, working from eaves to ridge. Fix using clout nails or a staple gun at each rafter, ensuring the membrane is taut but not over-tensioned, as some drape between rafters aids drainage. Store rolls upright in a dry location away from prolonged UV exposure before installation.
Does a 120GSM breathable membrane remove the need for roof ventilation?
In most cases, yes. A vapour-permeable underlay at 120GSM allows moisture vapour to pass through the membrane and dissipate, so a separate ventilation gap between the underlay and insulation is not required. Always check current building regulations and the tile manufacturer's guidance for your specific roof build-up.
How many rolls do I need for my roof?
Each roll covers 50 square metres at 1 metre wide. Measure the total rafter slope area of your roof, then add approximately 15% to allow for overlaps at horizontal and vertical laps. For a straightforward calculation on site, divide the total slope area by 50 and round up to the nearest whole roll.
Can this membrane be used on a cold roof as well as a warm roof?
Yes. The BreatheShield 120GSM membrane is suitable for both warm roof and cold roof construction, ventilated or non-ventilated, whether laid fully supported over sarking boards or unsupported directly over open rafters.
Nottage Timber Merchants supply breathable roof membrane alongside a wide range of sheet materials including OSB boards, available to trade and retail customers across Bridgend and South Wales, with next-day delivery options to the local area. Call or order online to confirm stock and quantities.
