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.
Warm deck flat roof insulation thickness.
There are two basic categories of roof design.
A flat roof where the insulation sits below the waterproof membrane and above the structural deck is a warm roof deck.
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.
Warm flat roofs do not need to be ventilated as the insulation is.
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.
A cold roof has the insulation placed below the structural deck which thus remains cold.
The definition of a flat roof according to bs 6229 is having a pitch less than 10 o to the horizontal however some in the industry would consider up to 15 o as their definition of a flat roof.
To calculate u values and insulation thickness specific to your project use our free online u value calculator.
To use epdm for a warm deck flat roof construction solid closed cell roof insulation such as kingspan or celotex should be placed on top of the roof deck rather than in between the rafters.
Others would treat even steeper pitches as flat roofs.
Warm deck flat roof insulation is now the standard way to insulate a flat roof click to enlarge flat roofs for example on extensions bathrooms and dormer windows are not the best of ideas.
Warm deck flat roofs can be constructed on most modern construction material types such as concrete timber and timber based sheets.
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.
They lose loads of heat and are prone to leaking causing the materials to deteriorate.
The joist size depends on your span but assuming you are going out say 3m or so your joists would be about 150 deep.
Min 125 thickness of insulation board then finish on top.
The below u value table shows the required insulation thickness based on the typical warm flat roof construction outlined.
The required thickness of quinn therm flat roof insulation will depend on the desired u values.
A warm roof has the insulation above the structural deck which is thus kept warm.
Add to this the firring pieces for slope say 75 max.
The waterproof layer is above the insulation and a vapour control layer is placed below the insulation.
