Cold Deck Flat Roof Detail

It is universally recommended that cold deck flat roof construction should be avoided.

Cold deck flat roof detail.

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. The insulation boards in an inverted warm deck are laid over the structural deck and the waterproof covering. Hopefully this video will help explain the difference between cold flat roof construction and warm flat roof construction this videos show detailed drawings. In terms of the thermal design of a flat roof what are the options and the best practices of flat roof build ups.

This is known as a cold roof because the roof deck and roof space are close to the external air temperature. Details both in 2d and 3d to give a clear understanding. Others would treat even steeper pitches as flat roofs. When building a flat roof it is vital that a degree of falls is built into the construction to ensure rainwater run off.

Cold deck roof 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. Similar to the pitched roof a flat roof can be insulated as a cold or a warm deck. The position of the insulation dictates which type it is. The epdm rubber roof membrane is then installed using the contact adhesive onto the deck.

The 18mm roof grade deck is then fixed on top of the rafters leaving suitable air flow between the insulation and the deck. The recognised flat roof build ups for best design practices are. The sandwich warm deck roof is the most common type of flat roof. Introduction warm cold roofs this guidance offers guidance on the difference benefits between warm and cold roofs.

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. In the case of a flat roof insulation is usually either a rigid board above the deck or a mineral glass wool quilt immediately. The definition of a flat roof according to bs 6229 is having a pitch less than 10 o to the horizontal however some in the industry would consider up to 15 o as their definition of a flat roof.

The insulation is placed below the waterproof covering and is either mechanically fixed or bitumen bonded on to the top of the deck. There must be an adequate void minimum 50mm between the deck and the insulation traditionally mineral wool to allow free movement of air and to prevent moisture vapour being transmitted from the building outwards where it could condensate in the roof. Flat roof details and information relating to insulating a flat roof.