When it comes to selecting a premium roofing underlay, not all breathable membranes are created equal. Cromar Vent 3 Pro Breathable Membrane stands out as the go‑to choice for roofing contractors and DIY enthusiasts across the UK. Engineered for superior performance in both warm and cold roof systems, Vent 3 Pro delivers exceptional protection against moisture, wind‑driven rain, and dust—while allowing trapped water vapour to escape.

What Is a Breathable Roofing Membrane?

A breathable roofing membrane (also called a breather membrane) is a water‑resistant underlay that permits water vapour from inside the roof structure to pass through, preventing condensation build‑up, but blocks external moisture and wind‑driven rain. This dual function helps maintain the integrity of insulation, rafters, and interior finishes—prolonging the lifespan of your roof.

Key Features of Cromar Vent 3 Pro

• 3‑Layer Micro‑Porous Construction
  Vent 3 Pro comprises a micro‑porous polypropylene film sandwiched between two layers of tough fabric, ensuring both breathability and waterproofing in one high‑performance roof underlay.

• High Vapour Permeability (Sd 0.02)
  With a water vapour transmission value (Sd) of just 0.02 m, moisture generated inside your home escapes quickly and efficiently, reducing risks of mould and rot.

• Waterproof Protection (Class W1)
  Tested in accordance with BS EN 13859‑1, Cromar Vent 3 Pro achieves a Class W1 rating for resistance to water penetration, defending your roof against wind‑driven rain and snow.

• Outstanding Strength & Tear Resistance
  Tensile strength of MD 320 N/50 mm and TD 270 N/50 mm, plus nail tear values of MD 290 N and TD 270 N, give Vent 3 Pro the durability to withstand site handling and challenging weather during installation.

• UV Stability (3‑Month Exposure)
  The membrane’s light‑green upper surface is UV‑stable for up to three months, allowing ample time to complete roof works without compromising performance.

• BS 5534 Compliant
  Proven suitable for all batten gauge configurations—345 mm, 245 mm, taped laps, and integral tapes—Vent 3 Pro meets the requirements of BS 5534 2014 Annex A for all UK roof zones.

Benefits in Warm and Cold Roof Applications

Cromar Vent 3 Pro excels in both warm and cold roof designs. In cold roofs, it sits directly under tiles or slates to protect the structure from external moisture while keeping loft spaces ventilated. For warm roofs, it can be draped over rafters or laid over insulation boards, ensuring continuous protection and vapour control 

• Either way, you get:

  • Reduced condensation and mould risk

  • Improved energy efficiency by safeguarding insulation

  • Extended roof deck longevity

  • Versatility across tiled, slated, and metal roofs.