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