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Breathable Roof Membrane Underlay 120GSM | 1m x 50m Roll
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.
Specifications
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
What it's used for
Underlaying concrete, clay or natural slate roof tiles on pitched domestic and commercial roofs
Warm roof and cold roof construction where vapour permeability removes the need for a separate ventilation gap
Full supported or unsupported installation over rafters or sarking boards
Refurbishment and re-roofing projects where the existing sarking felt is being replaced
Fitting and handling
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.
FAQ
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.
