The Cromar 3H Vent Base Layer 34kg 20m is a high-performance breathable roofing underlay designed to provide reliable secondary weather protection beneath tiled or slated pitched roofs. Manufactured from durable, lightweight materials, this vented base layer allows moisture vapour to escape from the roof space while helping to prevent water ingress from external elements such as wind-driven rain and dust. Supplied in a 34 kg roll with a coverage length of 20 m, it offers strong tear resistance and good handling characteristics, making installation quicker and more efficient for roofing professionals. The membrane helps improve roof ventilation and contributes to the long-term durability and performance of the roof structure.
Cromar 3H Vent Base Layer 34kg 20m
£79.12 inc. VAT
£65.93 ex. VAT
- Brand: cromar
- Manufactuer: cromar
The Cromar 3H Vent Base Layer 34kg 20m is a high-performance roofing underlay designed for use as a breathable base layer beneath roof coverings such as tiles or slates. It is typically installed on pitched roofs to provide a protective barrier against wind-driven rain, dust, and moisture while allowing trapped water vapour from inside the building to escape, helping to reduce condensation within the roof structure. The 20-metre roll and 34 kg weight provide durable coverage suitable for both new build and roof refurbishment projects, and the material is designed to improve roof ventilation while supporting the overall weatherproofing and longevity of the roofing system.
The Cromar 3H Vent Base Layer (34 kg, 20 m) is a perforated bitumen roofing felt designed for use as the ventilating base layer in multi-layer built-up roofing systems. It is typically installed as the first layer on flat roofs before additional underlay and cap sheets are applied, allowing trapped moisture vapour within the roof structure to disperse and helping prevent blistering or delamination of the upper waterproofing layers. The membrane generally consists of a glass-fibre reinforced core coated in oxidised bitumen with a sanded finish, providing good flexibility, adhesion, and durability during installation. It can be used on a range of substrates such as concrete, timber, and metal deck roofs when applied as part of a traditional pour-and-roll felt system. However, it is not intended to act as the final waterproofing layer and must always be overlaid with suitable roofing felts or cap sheets. Its performance also depends on correct installation in accordance with roofing standards and manufacturer guidance; improper detailing, insufficient bonding, or exposure without protective layers may lead to reduced effectiveness and potential moisture ingress.
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| Elementlength | |||||||
| up to 1,5 m |
up to 2,5 m |
up to 3,5 m |
up to 4,5 m |
up to 2,5 m |
up to 3,5 m |
up to 4,5 m |
|
| Type of window frame material |
Minimum witdth of joints for a butled mounting b in mm |
Minimum witdth of joints for a inner mounting b in mm |
|||||
| Hard PVC (white) | 10 | 15 | 20 | 25 | 10 | 10 | 15 |
| Hard PVC and PMMA (dark) (colour extruded) |
15 | 20 | 25 | 30 | 10 | 15 | 20 |
| Hard PUR integral foam | 10 | 10 | 15 | 20 | 10 | 10 | 15 |
| Wood-aluminium-window | 10 | 10 | 15 | 20 | 10 | 10 | 15 |
| Aluminium-plastic sandwich frame (bright) |
10 | 10 | 15 | 20 | 10 | 10 | 15 |
| Aluminium-plastic sandwich frame (dark) |
10 | 15 | 20 | 25 | 10 | 10 | 15 |
| Wooden window frame | 10 | 10 | 10 | 10 | 10 | 10 | 10 |
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