Cromar Vent 3 Pro Green is a 165g triple-layer breather membrane for tiled, slated and metal roofs. Suitable for warm and cold roof applications, supported or unsupported, with no additional ventilation required.
Size
QTY
Price
QTY
1.5m x 50m
20
£1,100.00£1,320.00
1.5m x 50m
54
£2,754.00£3,304.80
1m x 50m
20
£760.00£912.00
1m x 50m
54
£1,836.00£2,203.20
The Cromar Vent 3 Pro Green roofing membrane is a 165g triple-layer breather membrane built from high tensile spun bonded polypropylene outer layers with a micro-porous polypropylene film sandwiched between them. That construction is what gives it genuine waterproofing in one direction and genuine vapour permeability in the other. It is not a compromise between the two. It does both, properly.
This is a membrane roofers reach for when they need something that will perform across a range of roof types without having to second-guess the specification. Fully supported over insulation or draped unsupported across rafters, the Cromar Vent 3 Pro handles both without fuss. Tiled roofs, slated roofs, metal roofing systems — it is designed to work across all of them, whether you are building warm roof or cold roof.
What Makes the Cromar Vent 3 Green Worth Specifying
The membrane allows water vapour to escape from within the roof structure while blocking wind-driven rain, snow ingress and dust that works its way past the primary weathering layer. That balance is critical in the UK, where you need resistance against horizontal rain on a bad November afternoon and enough breathability to stop condensation rotting out the timbers beneath. Get either wrong and someone is back on that roof inside a decade.
Tensile and tear strength are genuinely good here. Lightweight and flexible enough to handle easily on site, it does not behave like a stiff board in cold weather, which matters when you are trying to lap and fix at height in January. The dark green printed upper face and white under-face also make orientation obvious at a glance, which sounds minor until you have watched someone install a membrane upside down.
UV stability is rated to four months’ exposure, so if a project stalls or the battening gets delayed, the membrane is not going to degrade sitting uncovered on a roof over the winter. No additional ventilation is required when this product is correctly installed, which simplifies the overall roof build and can save meaningful time on larger jobs.
Pro Tip: When lapping rolls, ensure a minimum 150mm side lap and 300mm end lap, and always fix through the laps into the rafter to stop wind uplift getting under the membrane before the battens go on.
Cromar Vent 3 Pro Green is used on pitched roofs across new build, refurbishment and re-roofing projects. It sits beneath tiles, slates and metal roof systems as a second line of defence against water ingress while allowing the roof structure to breathe. Roofers use it on both warm roof builds, laid directly over insulation, and cold roof configurations draped over rafters.
It is equally at home on domestic extensions and larger commercial or agricultural roofing projects where a reliable, code-compliant breather membrane is needed at scale. The 50m roll length and two available widths mean it suits a range of rafter and batten layouts without excessive off-cutting.
Best For
Pitched tiled roofs
Slated roof systems
Metal roof systems
Warm roof applications
Cold roof applications
New build and re-roofing
Compatible With
Fully supported installations over insulation
Unsupported installation over rafters
Timber rafter roof structures
Standard roofing batten and counter-batten systems
Key Properties
165g triple-layer construction
Micro-porous polypropylene film core
High tensile and tear strength
Waterproof and vapour permeable
UV stable up to 4 months
No additional ventilation required
Dark green upper face, white under-face
Available in 1m x 50m and 1.5m x 50m
Not suitable for: Not suitable for flat roof applications. Not intended as a primary waterproofing layer on any roof system.
Roll out the membrane horizontally across the roof, starting at the eaves and working upward. Keep the dark green face uppermost. Lap each course over the one below by a minimum of 150mm at side laps and 300mm at end laps. Fix through the laps into the rafters using clout nails or a suitable staple gun before the laps are covered by battens.
On unsupported installations, take care not to over-tension the membrane between rafters. A slight drape allows any water that does penetrate the tile or slate layer to run down and away rather than pond. Batten immediately after laying to secure the membrane and protect it from wind uplift. Where the membrane is exposed, bear in mind the four-month UV limit and batten promptly on longer projects.
Check roof structure is sound, clean and free from sharp projections before laying
Fix a continuous eaves protector or eaves course to support the membrane at the overhang
Start the first roll at the eaves with the green face uppermost, allowing a slight drape between rafters on unsupported installations
Fix the membrane temporarily with clout nails or staples through the top edge into the rafter
Roll out subsequent courses working up the roof, overlapping each by a minimum of 150mm at side laps
Maintain a minimum 300mm overlap at all end laps, staggering joints between courses where possible
Fix through laps into the rafters before covering with battens to prevent wind uplift
Install counter battens and tiling battens immediately after laying to secure the membrane fully
Seal all penetrations such as pipe outlets and dormer cheeks with compatible self-adhesive flashing tape
Does Cromar Vent 3 Pro Green require additional roof ventilation?
No. When correctly installed, Vent 3 Pro Green provides sufficient vapour permeability to manage moisture within the roof structure without the need for additional ventilation products such as ridge or soffit vents. This is one of the practical advantages over lower-spec membranes that still require a ventilated air gap.
Can this membrane be left exposed on the roof before battening?
Yes, for up to four months. The membrane carries a UV stability rating of four months, which covers most reasonable delays between roofing stages. Beyond that, degradation of the outer layer could affect performance, so battening sooner is always better practice.
Which width should I order for my project?
The 1m wide roll suits tighter rafter spacings or jobs where handling a wider roll is awkward, such as steeper pitches or confined loft conversions. The 1.5m wide roll covers more area per course and is generally faster to lay on straightforward open roof areas, reducing lap frequency and speeding up the job.
Cromar Vent 3 Pro Green is a 165g per square metre triple-layer membrane comprising two outer layers of high tensile spun bonded polypropylene with a micro-porous polypropylene film core. The micro-porous film is the functional layer, controlling vapour transmission while acting as a barrier to liquid water. The polypropylene construction provides long-term durability and resistance to biological degradation within the roof environment.
Weight
165g per m²
Construction
Triple-layer spun bonded polypropylene with micro-porous polypropylene film core
Roll Size (Option 1)
1m x 50m
Roll Size (Option 2)
1.5m x 50m
Upper Face Colour
Dark green (printed)
Under Face Colour
White
UV Stability
4 months exposure
Application Type
Warm and cold roof, supported and unsupported
Additional Ventilation Required
No
Suitable Roof Types
Tiled, slated, metal
Size
1.5m x 50m, 1m x 50m
Box Quantity
20, 54
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