U-value

The rate at which a material conducts heat. Polymers and cellular foams have low conductivity and act as insulators, while metals conduct readily, a contrast that matters in roof build-ups, battery enclosures and mould tooling.

Localised paths of increased heat flow through an insulated construction where a more conductive element, such as a metal fixing, rafter or parapet junction, bypasses the insulation. Thermal bridges increase heat loss and can produce cold internal surfaces that lead to condensation and mould growth.

Rigid insulation boards manufactured or cut to a wedge profile and laid to a designed scheme to create drainage falls on a flat roof, avoiding the need for screeds or firrings. Schemes combine tapered and flat boards to achieve both the required fall and the target U-value.

A roof construction in which the thermal insulation is placed above the structural deck, keeping the deck and supporting structure at close to internal temperature. A vapour control layer is normally installed on the warm side of the insulation to limit the risk of interstitial condensation.