Cold Roof
/kohld roof/
Also known as: cold deck roof, cold flat roof, ventilated roof, cold loft, cold roof construction
Definition
A roof construction in which the insulation is placed at ceiling level between and over the joists rather than above the structural deck. The roof void above the insulation remains cold and must be cross-ventilated to prevent interstitial condensation. The opposite of a warm roof.
In Practice
Cold roofs were the standard flat roof construction until the 1990s but are now largely superseded by warm roof design. Problems arise when ventilation is inadequate - moisture-laden air enters the cold void and condenses on the underside of the deck, causing rot and mould. BS 6229 still permits cold roofs but requires a minimum 50mm ventilated airspace above the insulation with cross-ventilation openings of at least 0.4% of roof area on two opposing sides.
UK Building Regulations
Approved Document L - Conservation of Fuel and Power
Cold roof construction for flat roofs is permitted but warm roof design is strongly preferred as it avoids the ventilation requirements and condensation risk inherent in cold roof construction.
See Also