A warm roof has the insulation above the structural deck which is thus kept warm.
Cold deck flat roof design.
A cold roof has the insulation placed below the structural deck which thus remains cold.
The insulation is placed below the waterproof covering and is either mechanically fixed or bitumen bonded on to the top of the deck.
This therefore leaves the roof and timbers cold requiring a breathable membrane between the insulation and roof.
Where a cold flat roof does incorporate insulation this is in the form of mineral wool.
Which makes sense as this space is otherwise empty and so it s a simple low impact way to insulate a roof.
In the case of a flat roof insulation is usually in the form of either a rigid board above the deck or a fibrous quilt immediately above the ceiling depending on the type of roof construction.
Warm cold and inverted.
Contrasted with the cold deck roof this construction has a much lower risk of condensation as the void will be of a comparable temperature to the roof.
Cold flat roof designs.
Inverted warm deck roof.
The waterproof layer is above the insulation and a vapour control layer is placed below the insulation.
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.
The insulation boards in an inverted warm deck are laid over the structural deck and the waterproof covering.
A cold roof design usually leaves a 50mm gap between the top of the insulation and the roof deck above.
Flat roof design guide.
The sandwich warm deck roof is the most common type of flat roof.
Hopefully this video will help explain the difference between cold flat roof construction and warm flat roof construction this videos show detailed drawings.
There are two basic categories of roof design.
The alternative roofing insulation design places the insulation layer between or under the timber rafters level with the ceiling joist.
Well a cold roof is created by laying insulation between the rafters.
Traditionally flat roofs simply consisted of a structural timber deck with a waterproof covering directly applied to the top of the deck.
So what exactly is a cold roof.
The recognised flat roof build ups for best design practices are.
In cold and very cold climates selecting a roof deck condensing surface temperature criteria of 45 f is very conservative.
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 three recognised designs of flat roof construction.
Can be slightly more difficult to install than a cold roof design.
