Each build is unique and we’ll work with you to shape the best possible solution for your green roof. Flat roofs Flat roofs have always been a very cost-effective and convenient form of roof- construction, but even the development of better roofing technologies has not prevented flat roofing from continuing to be prone to traditional defects such as leakage, component decay and, in the more extreme cases, structural failure. Millions of pounds a year are spent on the refurbishment of flat roofing – from simply patching, re-coating / re-covering through to the more comprehensive stripping off and replacement of the entire roof. Prevention of condensation Along with leakage, flat roof and in particular domestic scale timber roofs, are notoriously subject to the effects of condensation. Understanding the why this is the case, the links between thermal performance, air leakage and condensation, is critical to the successful design of a flat roof. Condensation occurs where warm, moisture-laden air comes into contact with a cold surface. In the case of a flat roof, moist warm air rises from the room below through the coverings and plaster into the roofing fabric where it risks condensing on the underside of the roof decking/ water-proof membrane. Cold roof Part of the successful design of a flat roof is in preventing such a condition from occurring. The choice of construction theoretically rests on two different methods of handling moist air. In traditional flat roof construction, it is prevented from penetrating the roof fabric from the building below through the use of a vapour control layer at ceiling level. Any residual water vapour entering the roof dispersed through cross-ventilation provided by eaves vents or proprietary ‘mushroom’ vents projecting through the roof: a ‘cold roof’ Warm roof More recent design practice is to inhibit the moist air from condensing by keeping the roof deck at near room temperature through insulation and preventing water vapour from penetrating further by provision of a vapour control layer (VCL) above the deck – a ‘warm roof’. Condensation might still occur under a thin deck, particular in the case of an ‘inverted’ warm roof where rain run-off can lead to rapid cooling, but can be averted by internal temperatures and / or the use of a deck material with a high thermal capacity. In practice, because of the loss of heat and relative difficulty of providing adequate ventilation, ‘cold’ roof construction has largely been discontinued and in Scotland, banned.