Warm Roof
/worm roof/
Also known as: warm deck roof, warm flat roof, above-deck insulation, inverted roof
Definition
A flat roof construction in which the insulation layer is placed above the structural deck, keeping the deck and structure within the warm conditioned envelope of the building. This avoids interstitial condensation risk and is now the dominant approach for flat roofs.
In Practice
In a warm roof the build-up from bottom to top is: structural deck, vapour control layer, insulation (PIR or XPS boards), waterproof membrane. The alternative - a cold roof with insulation between joists - requires cross-ventilation above the insulation and is prone to condensation problems. Warm roofs are strongly preferred under current Building Regulations Part L.
UK Building Regulations
Approved Document L - Conservation of Fuel and Power
BS 6229 covers flat roof design and construction. A warm roof construction is strongly preferred as it avoids the condensation risk inherent in cold roof designs. Part L sets the maximum U-value for flat roofs at 0.18 W/m2K.
See Also