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IMPLICATIONS OF THE NEW NHBC ROOF VENTILATION DIRECTIVE
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The NHBC'S newly published ventilation requirements apply to all home starts from 1st January 2011. Klober examines the implications….
The issue of how best to control condensation in roof spaces has been debated ever since vapour permeable underlays (VPUs) were introduced. Recent cold winters, however, have put the performance of some VPUs in the spotlight following an increasing number of calls concerning roof condensation to the NHBC.
The risk of condensation in new homes is at its greatest during the drying out period. Until now, 'unventilated' roofs have been considered acceptable for VPUs supported by BBA or similar certification. However, by stating that supporting ridge or high level ventilation equivalent to a continuous opening of 5mm must now be provided, the NHBC has decided that such certification can no longer be considered adequate.
It is important to highlight, however, that this is only relevant when seeking the NHBC warranty, and applies only to VPUs and not to air-open underlays. Unlike VPUs, however, there are currently only two proprietary air-open membranes available, the best performing being Klober Permo Air.
Klober's portfolio of products uniquely covers all 3 ventilation options.
- An air-open membrane with no ventilation (Klober's product is Permo Air)
- Vapour open membrane with high level ventilation (Klober products are Permo Forte/Light/Ecovent with Roll Fix Ridge, or Vent Tiles)
- Vapour closed membrane with eaves and ridge ventilation (Klober products are Sepa Forte/Light with components)
A comprehensive range of air barriers, vapour control layers, tapes, sealants and sealing collars also provides scope for airtight construction for the most complex roofing specifications as we move towards zero carbon house building.
Klober MD David Arendell added “Ventilation best practice is of course no less relevant to refurbishments, particularly in situations such as public sector housing upgrades. Airtightness may not yet be a requirement and ceilings are less likely to be well sealed in cold roof design. However, it should be considered in order to limit condensation risk within the roof void. In terms of ventilation of the roof space it is ironic that by seeking to reduce long-term maintenance costs, the widespread use of ventilated dry ridges and hips by housing associations has reduced the likelihood of problems with VPUs.”
