Warm Flat Roof Insulation Thickness

There are two basic categories of roof design.

Warm flat roof insulation thickness.

The chosen insulation laid on top of this should be able to take the weight of anything put above it on the roof without compression or protected from compression by further sheeting. However if we do not include removal of old roofing you are looking at about 7 50 to 9 00 per foot of roofing plus about 2 50 to 3 00 per foot of 5 thick insulation say about 10 12 per square foot. There are two types of flat roof. Inverted roofs are a type of warm flat roof where the insulation is above the waterproofing layer.

The typical u value of an existing uninsulated flat roof is 1 5w m2k. Thickness varies according to the manufacturer s specifications. These are can be supplied with rebated edges which interlock reducing the risk of uplift. Achieving a u value of 0 20w m meaning your roof will be better insulated than your walls will need 120mm thickness of rigid foam or 200mm of mineral wool or natural insulation.

Cold flat roofs are typically avoided as you d need to install ventilation which can prove problematic for many reasons relating to space labour costs etc. Cold roofs and warm roofs. In this case ventilation is required and the roof can still become wet with condensation which may cause materials to decay. Warm flat roofs do not need to be ventilated as the insulation is.

A flat roof where the insulation sits below the waterproof membrane and above the structural deck is a warm roof deck. A warm roof has the insulation above the structural deck which is thus kept warm. The waterproof layer is above the insulation and a vapour control layer is placed below the insulation. The insulation material for a warm flat roof should.

Ventilation is required for these roofs. A cold roof has the insulation placed below the structural deck which thus remains cold. Flat roof insulation thickness. Cold deck this is where the insulation is placed between the joists rafters or in between the ceiling joists in the case of a pitch roof.

Insulation in a warm roof. The insulation for a warm roof will usually be boards of extruded polystyrene or rigid compressed boards of glass fibre or rock fibre. This is placed over the roof joists and a board normally external ply is laid on top. Cold roofs have the waterproof layer placed directly onto the roof deck and the insulation inside the roof just above the ceiling.

This means that the insulation should be highly resistant to water absorption for example an extruded polystyrene based product which will not be affected by water or repeated freeze thaw cycles. With a flat roof this issue does not arise but the u value constraint and the amount of insulation needed is just the same.