The below u value table shows the required insulation thickness based on the typical warm flat roof construction outlined.
Warm deck flat roof insulation thickness.
Cncd 053 v1 5 7 2019 0 cold deck flat roof the thickness of insulation required will vary depending on the material you decide to use and the manufacturer s specification.
The required thickness of quinn therm flat roof insulation will depend on the desired u values.
18 thickness of deck.
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 waterproof layer is above the insulation and a vapour control layer is placed below the insulation.
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.
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.
Ventilation is required for these roofs.
There are two basic categories of roof design.
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.
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.
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.
Warm deck flat roofs can be constructed on most modern construction material types such as concrete timber and timber based sheets.
They lose loads of heat and are prone to leaking causing the materials to deteriorate.
A cold roof has the insulation placed below the structural deck which thus remains cold.
Add to this the firring pieces for slope say 75 max.
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.
To calculate u values and insulation thickness specific to your project use our free online u value calculator.
A warm roof has the insulation above the structural deck which is thus kept warm.
Others would treat even steeper pitches as flat roofs.
When building a flat roof it is vital that a degree of falls is built into the construction to ensure rainwater run off.
