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Products
Where a vapour control layer has been shown by calculation to be necessary, this could consist of a polyethylene membrane (such as Sarnafil EcoVap or SarnaVap) or reinforced bitumen sheet.
In either case, the inclusion of metal foil laminate greatly increases the water vapour resistance of the product.
Independently certified test data for the product should verify that is has adequate performance against the following criteria:
- Resistance to heat ageing
- Resistance to UV (during construction and storage)
- Tear resistance
- Consistent vapour resistance
- Tensile strength
Regardless of the material type used, the vapour control layer should be carried up at least as high as the upper edge of the insulation layer, at perimeters and at all upstands and penetrations. Where there is a risk of high internal vapour drive (e.g. swimming pools, laundries, etc.) care should be taken to minimise potential risk of reduced vapour control layer performance, caused by fastener penetration.
Bitumen Sheet Vapour Control Layer
Bituminous sheet vapour control layers are generally bonded in hot bitumen, cold bitumen bonding compound, synthetic adhesive or can be self adhesive. Occasionally they are nailed when the substrate is timber. They can be either fully or partially bonded, with head and side laps sealed with suitable adhesive during the laying process. Correct installation processes are described in BS 6229: 1982: Section 4: Clause 26.3.
Where possible, all penetrations of the vapour control layer should be sealed as appropriate to the use of the system. If the VCL membrane may come into contact with an incompatible single ply material, detail work should be finished as recommended by the membrane manufacturer. The VCL should be turned up to all vertical surfaces by the thickness of the insulation. Where applicable, sufficient additional material should be retained at the perimeter, to enable it to be sealed to a suitable surface of the perimeter to form an air and moisture vapour seal.
Polyethylene Vapour Control Layers
Polyethylene sheet vapour control layers are not currently covered by a relevant British Standard. They are generally loose laid under mechanically fastened or ballasted systems and should be loose laid with all side and head laps fully lapped and sealed with an appropriate non-setting adhesive tape, in accordance with the manufacturers specification.
Where possible, all penetrations of the vapour control layer should be sealed as appropriate to the use of the system. The VCL should be turned up to all vertical surfaces by the thickness of the insulation. Where applicable, sufficient additional material should be retained at the perimeter, to enable it to be sealed to a suitable surface of the perimeter to form an air and moisture vapour seal.
© 2006 Sarnafil Ltd. Legal Disclaimer
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