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Chesterbreathe Breathable Membranes -
Guide to Fixing

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Chesterbreathe should be laid parallel to the eaves and draped over the rafters (Diagram 1 - unsupported construction) or laid directly over rigid insulation boards (Diagram 2 - fully supported) where the use of counter battens would be recommended.

When using Chesterbreathe without full eaves and ridge ventilation, attention should be paid to limit the amount of water vapour transfer into the loft space from the dwelling below. This would include sealing all loft hatches and penetrations into the roof space. The dwelling below the roof space must be ventilated in accordance with National Building Regulations, extractor fans should be used in areas of high humidity, i.e. bathrooms and kitchens, all water tanks and pipes in the loft should be lagged. To limit the amount of vapour transfer through the insulation (fitted at ceiling or rafters level), the use of a suitable vapour control layer is recommended. With a vapour resistance at least seven times greater than that of the breathable membrane. The use of vapour check plasterboards may also be considered where appropriate. The air tightness of the slate/tile assembly should also be assessed when considering the total ventilation requirements.

Minimum Overlap
Roof Pitch
Horizontal Lap (mm)
Vertical Lap (mm)

12.5° - 14°

225

100

15° - 34°

150

100

35° +

100

100

The rolls must be attached using galvanised clout nails or corrosion resistant staples with any exposed fixing sealed or covered, vertical overlaps must lie on the rafters. Ensure the surface is clean, to avoid mechanical damage to the membrane for which the manufacturer accepts no liability. Any damage must be rectified immediately, care and other attention must be taken during and after installation to avoid unnecessary damage to the integrity of the membrane which may not be visible. Keep cuts for roof penetration (extraction pipes, windows, flues) as small as possible and then completely seal.

All overlaps may be sealed with suitable tapes if required to form a sealed roof system.

A special eaves protector is recommended in the vulnerable gutter area such as Chesterflex BS747 type 5U eaves sheet

Diagram 1 (unsupported) - The following specification is a typical cold roof application

Diagram 2 (fully supported) - The following specification is a typical Warm roof application

 

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