Cold Deck Flat Roof Detail

The recognised flat roof build ups for best design practices are.

Cold deck flat roof detail.

Similar to the pitched roof a flat roof can be insulated as a cold or a warm deck. The insulation boards in an inverted warm deck are laid over the structural deck and the waterproof covering. In the case of a flat roof insulation is usually either a rigid board above the deck or a mineral glass wool quilt immediately. This is known as a cold roof because the roof deck and roof space are close to the external air temperature.

When building a flat roof it is vital that a degree of falls is built into the construction to ensure rainwater run off. Introduction warm cold roofs this guidance offers guidance on the difference benefits between warm and cold roofs. 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. It is universally recommended that cold deck flat roof construction should be avoided.

Hopefully this video will help explain the difference between cold flat roof construction and warm flat roof construction this videos show detailed drawings. The position of the insulation dictates which type it is. Others would treat even steeper pitches as flat roofs. In terms of the thermal design of a flat roof what are the options and the best practices of flat roof build ups.

Inverted warm deck roof. 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. 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. Details both in 2d and 3d to give a clear understanding.

The insulation is placed below the waterproof covering and is either mechanically fixed or bitumen bonded on to the top of the deck. 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. Ventilation is required for these roofs. Flat roof details and information relating to insulating a flat roof.

The 18mm roof grade deck is then fixed on top of the rafters leaving suitable air flow between the insulation and the deck. The epdm rubber roof membrane is then installed using the contact adhesive onto the deck. The sandwich warm deck roof is the most common type of flat roof.