Chesterfelt 3B - Torch-On Felt Underlay - 20m x 1m

Chesterfelt 3B - Torch-On Felt Underlay - 20m x 1m is a underlay felt for felt / bituminous flat roof system applications, helping create reliable waterproof protection on flat roofs.

This underlay felt is used as part of a built-up felt roof system to create layered waterproof protection. It is commonly used on garages, extensions, dormers, porches and outbuildings, either over new OSB/plywood decking or suitable existing felt overlays where the full system allows.

Best for

• Built-up felt flat roof systems
• New boards or compatible existing felt overlays

Key features

• Brand: Chesterfelt
• Glass reinforced
• Sanded finish
• Roll weight: 40kg
• System type: Felt / bituminous flat roof system
• Designed for long-lasting waterproof protection when installed as part of the correct system
• Commonly used as an underlay beneath felt shingles
• Roll size: 20m x 1m

Application / installation

• Recommended for competent DIY or trade installation depending on the roof system and project size
• Install in dry, suitable conditions unless the specific product states damp-weather application is allowed
• Surface must be clean, sound and prepared before application
• Allow for laps, overlaps and correct layer sequencing in the felt system

System components / used with

• Torch-on cap sheets, underlays and venting/base layers
• Bitumen primer, felt adhesive or mastic where specified
• OSB/plywood decks or compatible existing felt overlays
• Gas torch equipment and suitable PPE for hot works

Coverage

• Roll coverage: approx. 20m² before laps, overlaps and waste

Technical details

• It is recommended that an underlay such as 3B underlay, is applied on roofs with a pitch between 15 degrees and 45 degrees. Above 45 degrees the underlay is not required unless the building is in an exposed location.

Chesterfelt technical information

• Chesterfelt high-performance membranes are manufactured to ISO 9001 quality standards and are CE marked and UKCA to EN 13707:2004+A2:2009.

Things to consider before buying

• Coverage is approximate; allow extra for laps, overlaps, detailing and waste
• Check substrate compatibility before ordering: OSB, plywood, concrete and existing felt overlays may need different preparation
• Install in dry conditions and avoid unsuitable cold temperatures unless the product data allows otherwise
• The surface must be clean, dry and free from loose material before application