What is a Warm Roof?
Warm roofs are generally considered as very effective for energy use reduction and building performance as large slabs of high performance thermal insulation can be installed easily, and accredited details such as Sika’s Sarnafil BRE approved details minimise air leakage and thermal bridging.
In a warm flat roof construction, the Sika single ply membranes, liquid applied membrane or bitumen membrane waterproofing layer is installed directly over the thermal insulation layer with the air and vapour control layer (AVCL) sitting under the thermal insulation (warm side). This will prevent warm vapour from rising though the construction and condensating on the underside of the waterproofing where it could cause damage to the structure or fixings. In this type of roof design the structural deck (concrete), supporting structure and ceiling treatments are all kept at an ambient temperature close to that of the building’s interior.
Design Considerations
In a warm roof construction, there is no need to create ventilation paths, but the thermal insulation used needs to be sufficient grade and depth to maintain the vapour barrier above dew point temperature. To comply with BS 6229 and BS 5250, the building humidity classification needs to be established to ensure that the most appropriate grade of vapour barrier is selected for the project to avoid interstitial condensation issues. Sika carry out thermal and condensation risk analysis for every project inclusive of Sikatherm insulation to assist specifiers in this respect.
