Structural Elements
Condensing the right approach to roofing
Alun Price and Jenny Deacon, of Glidevale, look at roofing issues in modern build techniques
roofing ventilation is even more important. Even a building needs to breathe, and if you create a sealed box, it can’t! Logically, as insulation levels increase, so does
A
s we increase levels of insulation, and build increasingly airtight homes, the need for adequate and appropriate
the temperature difference between warm, occu- pied areas and cold, unoccupied areas, thereby increasing the potential for moisture in the inter- nal air to condense unless controlled, bespoke air passages exist for that moisture to escape to the outside atmosphere. The key is to construct the roof in such a way
Building Regulations require roof space ventilation of equivalent to a 10mm continuous gap at low level or 10,000mm2/m
that heat retention is optimised but any mois- ture can be effectively removed, in an efficient and cost-effective way, that minimises snagging and remedials: a ‘fix and forget’ solution. But, as with any aspect of building, the efficiency of the techniques is dependant on the quality of workmanship in the first place. Indeed, a new document published by CITB-Construction Skills, emphasises the need to check materials are properly installed, so they do not adversely impact on either their performance, of the performance of related materials – for example, insulation should not be laid so it covers/ obstructs roof space ventilation. Building component suppliers are bringing to
market products that utilise latest technology, such as low resistance (vapour permeable) and high resistance (non-vapour permeable) under- lays, and ventilators for eaves, roof and ridge. Many help the builder by reducing or removing the requirement for a high level of skill – for example, dry fix and mechanical fix. ‘Multi- tasking’ continuous aluminium dry fix ridge ventilation systems, for example, will last the lifetime of the building, while ventilating the ridge at high level in accordance with both BS5250 and the latest NHBC requirements, and overcoming the need for skilled mix and applica- tion of mortar. Firstly, however, the builder needs to decide
his construction process, and achieve it in such a way that it optimises airtightness while comply- ing with Regulations, yet still allows moisture to escape in a controlled manner. BS5250 is the main means of compliance with
regulatory requirements throughout the UK. In Scotland, Northern Ireland and Eire, BS5250 has
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