Warm Flat Roof Insulation Thickness

The insulation for a warm roof will usually be boards of extruded polystyrene or rigid compressed boards of glass fibre or rock fibre.

Warm flat roof insulation thickness.

Inverted roofs are a type of warm flat roof where the insulation is above the waterproofing layer. Saint gobain insulation uk manufacture and supply glass mineral wool slabs and rolls along with rigid polyisocyanurate pir boards that can be considered suitable for a wide range of applications across flat roofs whether you re looking to insulate at joist level or above the roof deck in your flat roof construction. Thickness varies according to the manufacturer s specifications. Cold roofs have the waterproof layer placed directly onto the roof deck and the insulation inside the roof just above the ceiling.

In this case ventilation is required and the roof can still become wet with condensation which may cause materials to decay. With a flat roof this issue does not arise but the u value constraint and the amount of insulation needed is just the same. There are two types of flat roof. Insulation in a warm roof.

Flat roof u value 0 18 w m2k 2 warm deck flat roof the type of insulation for this is usually of a rigid type and the thickness will vary depending on the manufacturer s specifications. 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. These are can be supplied with rebated edges which interlock reducing the risk of uplift.

Warm deck the type of insulation for this is usually of a rigid type and the thickness will vary depending on the manufacturer s specifications. 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. Flat roof insulation thickness. It should be of the maximum available thickness.

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. The typical u value of an existing uninsulated flat roof is 1 5w m2k. Cold roofs and warm roofs. 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.

Warm flat roofs do not need to be ventilated as the insulation is. This is placed over the roof joists and a board normally external ply is laid on top. 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.