By moving the insulation to the outside of the structure, the roof deck is effectively brought inside, which results in a 'warm deck' (hence the name), this removes the the possibility of condensation forming on the underside of the deck and eliminates damp. Because this design works by conserving heat, no ventilation is required. Modern polyisocyanurate (PIR) foam rigid insulation with reflective foil to both sides provides more than double thermal efficiency compared to mineral wool, and unlike the cold roof method the insulation thickness is not limited by the depth of the timber rafters/joists. A vapour barrier or vapour control layer is an essential component of any warm roof.

constructing a flat roof, giving the best thermal performance and vapour control, whilst maximising flexibility of design by reducing the need for natural ventilation. In general, any high risk condensation areas should have a Warm Roof construction. General advice for Warm Roof constructions can be found in BS 5250 : 2002. Care should be taken to ensure the chosen insulation can withstand the loads likely to be applied to the roof, particularly in balcony and walkway applications. We recommend when fixing to joist or metal deck, that a layer of plywood is incorporated prior to fixing the insulation, to act as a spreadsheet and avoid point loading. Standard Calculations based on British Standard BS.6229, exist for checking the thermal characteristics and condensation risk for a roof construction. It is recommended that whenever a warm roof is specified, and particularly over a humid environment, that these calculations are carried out. The majority of insulation manufacturers such as Kingspan provide a calculation service and our own technical department can provide standard calculations, if supplied with full construction and environmental details.