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Control of Condensation
Satisfactory performance in respect of the control of condensation, both on the surface of and within the roof system, is essential if thermal and durability targets are to be realised.
All designs should be checked in terms of condensation risk for the intended building function (and any future change of use). The Building Regulations Approved Documents F (F-1, Means of ventilation and F-2 Condensation in roofs) sets mandatory requirements in respect of the control of condensation.
Air Leakage
Approved Document L of the Building Regulations has introduced the requirement that the roof and those elements, which penetrate it, should be suitably airtight. It is anticipated that with effect from October 2003, the roof of a building with a gross floor area in excess of 1000m2 will comply with the requirement, if the permeability to air of the roof is tested to the procedures defined in CIBSE TM23. It should achieve permeability to air not exceeding 10m3/h/m2, at a reference pressure of 50Pa.
Buildings of less than 1000m2 gross floor area require a certificate of conformity, indicating that appropriate design details and building techniques have been used.
Control of Air Leakage
In a single ply roofing system, effective sealing against air leakage is achieved by either:
- A sealed deck (concrete or steel, with appropriate sealing at perimeters and penetrations and by incorporating sealant in the side and head stitching of the steel decks), or (more commonly and easily),
- A vapour control layer which, if properly sealed to the building perimeter and all penetrations, should provide a satisfactory seal. It is anticipated that mechanical fasteners driven through the vapour control layer will not affect permeability significantly, because the insulation is compressed onto the vapour control layer at each fastening point.
It is anticipated that whilst the current requirement is not onerous and is easy to achieve, it will become steadily more onerous with each revision of the Building Regulations.
Compatibility of Components
The selection of components within the roofing system should be discussed in detail with the manufacturer of the membrane, to ensure complete compatibility between components. Incorrect specification of incompatible components will lead to premature failure of the roofing system.
The correct choice of insulation (where applicable) is important when adhering the waterproofing, especially when solvent based adhesives are being used. The membrane and insulation manufacturer should always be consulted when selecting the insulation.
© 2006 Sarnafil Ltd. Legal Disclaimer
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