Permavent Apex Air/ Vapour Permeable Roofing Underlay - Air Open Vapour Open Membrane

A three‑layer breather membrane for pitched‑roof underlay, Permavent APEX combines vapour and air permeability with outstanding water‑resistance and condensation control. It forms a reliable secondary barrier against water ingress and removes the need for dedicated low‑ or high‑level ventilation in most standard roof builds.

Available in three formats

• Taped 50 – 1 m × 50 m roll with integrated double‑sided tape
• Untaped 50 – 1 m × 50 m roll, ready for use with site‑chosen tapes or sealants
• Untaped 75 – 1.5 m × 50 m roll for wider coverage when desired

All three meet the same rigorous performance standards and are fully compliant with BS 5534:2014 + A2 2018, suitable for installation across every UK wind zone.

Key Features & Benefits

• BBA‑certified for cold non‑ventilated, cold ventilated and warm non‑ventilated pitched roofs (up to 70° pitch)
• Air & vapour permeable (180 g/m²) to help manage moisture vapour inside the roof build
• Highly water resistant (W1 rating to EN 13589), keeping out wind‑driven rain
• UV‑stable for up to three months, allowing flexibility on site
• Taped version
  • Built‑in double tape speeds up laps and seals, reducing overall membrane usage by up to 25%
  • Ideal where labour or tape compatibility is a concern
• Untaped versions
  • Maximum flexibility to pair with your preferred tape or adhesive detailers
  • 75 cm width variant (Untaped 75) covers more area per run, cutting down installation time on wider spans

Whether you choose the convenience of integrated tape or the adaptability of untaped rolls (in either 1 m or 1.5 m widths), Permavent APEX delivers the same high‑performance breather membrane you can trust.