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.