With a flat roof this issue does not arise but the u value constraint and the amount of insulation needed is just the same.
Warm flat roof insulation thickness.
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.
A flat roof where the insulation sits below the waterproof membrane and above the structural deck is a warm roof deck.
The insulation for a warm roof will usually be boards of extruded polystyrene or rigid compressed boards of glass fibre or rock fibre.
Cold roofs have the waterproof layer placed directly onto the roof deck and the insulation inside the roof just above the ceiling.
Insulation in a warm roof.
It should be of the maximum available 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.
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.
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.
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.
This is placed over the roof joists and a board normally external ply is laid on top.
Inverted roofs are a type of warm flat roof where the insulation is above the waterproofing layer.
In this case ventilation is required and the roof can still become wet with condensation which may cause materials to decay.
Flat roof insulation thickness.
These are can be supplied with rebated edges which interlock reducing the risk of uplift.
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.
Ventilation is required for these roofs.
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.
There are two types of flat roof.
The typical u value of an existing uninsulated flat roof is 1 5w m2k.
The insulation material for a warm flat roof should.
