Cold Deck Roof Detail

Traditional cold deck flat roof traditionally flat roofs simply consisted of a structural timber deck with a waterproof covering directly applied to the top of the deck.

Cold deck roof detail.

Ventilation is required above the insulation in a cold roof to prevent the build up of moisture vapour in the roof void. Because the structural elements of a cold roof are not protected by from the heat of the sun by a layer of insulation they are liable to suffer the damaging effects of thermal movement. This cold deck construction is considered problematic in the humid temperate climate of the uk where the effective ventilation of restricted roof voids may be impractical particularly in sheltered built up areas. A cold roof construction will normally comprise of a structural deck on joists or purlins with a ceiling layer fixed to the bottom of the joists purlins thereby creating an air layer or cavity within.

A cold deck roof is where the insulation is placed between the joists rafters or in between the ceiling joists in the case of a pitch roof. Ventilation is required for these roofs. In a cold roof construction the sarnafil membrane is installed directly to the structural decking usually timber with firrings to fall. The epdm rubber roof membrane is then installed using the contact adhesive onto the deck.

Insulation would normally be placed in the lower portion of this void mostly sitting on or just above the ceiling structure. A warm roof construction allows heat to be conserved within a property without the need for a ventilation system. It is universally recommended that cold deck flat roof construction should be avoided. The insulation material is placed immediately above the ceiling between the rafters.

A warm roof construction has many benefits over a traditional cold roof essentially it is a breathable roof construction which allows moisture to escape which in turn prevents damp and any associated decay problems. A cold deck is constructed as follows.