- Product Description
- BBA certified
- Cold & warm roof application
- 3 layer spunbonded membrane
- Clean & easy to use
- Lightweight & flexible
- Excellent tensile strength
- Light grey surface prohibits glare
- UV stable for up to 3 months
- Requires no ventilation
Cromar Vent 3 Light Breathable Roof Underlay Felt 95gsm 50mtr x 1mtr / 50mtr x 1.5mtr
An economy breathable roof underlay for cold and warm roof applications which give major benefits over traditional roof underlays.
Cromar Vent 3 Light is a triple layer fabric, high performance breather membrane, made from high tensile spun bonded polypropylene layers, around a microporous polypropylene film.
Designed for use in a fully supported or unsupported tiled, slated or metal roof system.
The high vapour permeability and waterproof nature of the membrane, combined with excellent tensile/tear strength and high wind uplift resistance make Vent3 Light the professionals choice.
It is equally suitable whether draped unsupported over rafters or laid directly over insulation.
The outer layer forms the functional waterproof surface, the middle layer is the breathable waterproof membrane, and the inner layer protects the membrane from abrasion and damage,& also giving additional strength.
This enables the fabric to allow moisture vapour to pass through, whilst remaining fully waterproof.
The upper surface is Dark Grey, printed with the trade name and head lap lines.
Available in 1.0m and 1.5m widths as standard to conform easily to any typical roof configuration or the individual working practices of the installer.
- Weight: 95 g/m2
- Roll Size: 50m x 1.5m = 75 square metres / 50m x 1.0m = 50 square metres
- Roof Pitch:12.5 degrees - 14 degrees = Lap: 150mm
- Roof Pitch: 15 degrees - 34 degrees = Lap: 100mm
- Roof Pitch: 35 degrees+ = 75mm
- Vent3 Light must be installed in accordance with the relevant sections of BS 5534:2003 and the manufacturers fixing instructions
- Vent3 Light is designed as a secondary barrier to wind driven rain and snow, it should not be considered a primary waterproofing layer
- Whilst the product is UV stable for up to 4 months exposure, good roofing practice dictates that the primary waterproofing finish (e.g. tiles, slates etc.) be applied as soon as practically possible
- Under slating membranes should not be considered as temporary weatherproof protection for occupied buildings or where internal fitting out is taking place. Additional protection should be afforded in these circumstances.Vent3 Light should be unrolled across the roof, starting at the eaves and working up the roof, it is usually laid Dark Grey (printed) side up
- With normal slates and tiles the Vent3 Light membrane can be installed draped 10mm to 15mm into the void between the rafters, it can then be secured with the tiling battens
- This will leave sufficient space between the Vent3 Light and the tiles/slates for drainage and ventilation
- Vent3 Light when installed as a fully supported system, is laid over the support and secured with counter battens, alternatively the membrane can be installed over counter battens and fixed at 200mm centres using corrosion resistant straps or galvanised clout nails
- Tiling battens are fixed to the counter battens leaving a minimum airspace of 25mm between the roof sheet underlay and the tiles for drainage and ventilation
- In unventilated roof systems vapour control measures are required below the insulation layer to restrict the flow of moist air from within the inhabited building into the roof space
- Additionally, the building below should be ventilated in accordance with the Building Regulations with water tanks sealed
- Abutment flashing should be wedged into a mortar joint 25mm deep and at least 150mm above the level of the slates or tiles
- Vent3 Light underlay should be turned up behind the flashing at least 100mm to prevent rain and snow being blown into the roofspace
- 600mm reinforcing strips should be fixed at hips, ridges and valleys
- At the eaves felt support tray should be installed to prevent ponding behind the fascia
- The Vent3 Light should be laid over the support tray stopping short of the roof tile tails to prevent UV degradation of the underlay
- Notes: As with all breather membranes of this type, contact with solvents or wet timber & preservatives can cause localised water penetration to occur, prior to the main weatherproofing being installed
- In accordance with BS 5534: 2003 Section 22.214.171.124 (c), where a roof underlay or breather membrane is to be laid over open rafters, a drape of between 10mm to 15mm between the rafters is desirable to guide any rainwater penetrating the main roof finish away from the rafters to the drainage point. (The membrane must not be pulled tight against the underside of the tiling battens.)