Cold Deck Flat Roof Design

Warm cold and inverted.

Cold deck flat roof design.

Traditionally flat roofs simply consisted of a structural timber deck with a waterproof covering directly applied to the top of the deck. This temperature criteria can be reduced to 40 f which corresponds to interior average conditions of 70 f 35 rh where high interior moisture loads due to spas indoor swimming pools and excessive humidification are. There are two basic categories of roof design. If insulation is installed below the flat roof deck this is called a cold roof.

There are three recognised designs of flat roof construction. A cold roof has the insulation placed below the structural deck which thus remains cold. A cold roof is an easy option when creating a flat roof simply placing insulating between the rafters. The insulation boards in an inverted warm deck are laid over the structural deck and the waterproof covering.

The sandwich warm deck roof is the most common type of flat roof. The insulation in a warm deck roof is installed immediately below the roof membrane on top of the roof deck usually with a vapour control layer underneath the insulation. In cold and very cold climates selecting a roof deck condensing surface temperature criteria of 45 f is very conservative. Where a cold flat roof does incorporate insulation this is in the form of mineral wool.

A warm roof has the insulation above the structural deck which is thus kept warm. The recognised flat roof build ups for best design practices are. The insulation is placed below the waterproof covering and is either mechanically fixed or bitumen bonded on to the top of the deck. This design dates back many years and flat roof insulation was somewhat of an afterthought with this type of roof.

Inverted warm deck roof. Consider geography budget and use for the roof to determine the best option. The requirement for roof void ventilation in cold roofing designs means it is generally not recommended as a design for new build flat roofs. A note to consider before construction.

From there the flat roof system you choose will determine the materials you apply. Flat roof design guide. Cold roofing designs can be extremely tricky for existing. In the case of a flat roof insulation is usually either a rigid board above the deck or a mineral glass wool quilt immediately above the underdrawn ceiling depending on the type of roof design and construction.

Hopefully this video will help explain the difference between cold flat roof construction and warm flat roof construction this videos show detailed drawings.