What is a warm roof?

  • In a warm roof the thermal insulation is immediately below the membrane finish
  • The structural deck, any voids and the ceiling are at a temperature close to that of the building’s interior
  • Condensation control is achieved by using a vapour control layer (VCL) on the warm side of the insulation
  • The amount of insulation should be enough to maintain the VCL above dewpoint temperature
  • Warm roof voids are not ventilated
  • Condensation can be calculated to BS 6229 and BS 5250

In a warm roof construction the Sarnafil membrane and SarnaTherm thermal insulation is installed above the structural decking. In principle this keeps the structural deck (usually trapezoidal steel or timber) at more or less the same temperature as the inside of the building A vapour control layer is required underneath the insulation in to prevent moisture vapour being transmitted from the building outwards where it could condensate in the roof construction  (interstitial condensation).

Warm roofs are generally considered as very effective for energy use reduction and building performance.


However the thermal insulation type and thickness is critical.   

Sarnafil carry out thermal and condensation risk analysis for every project inclusive of SarnaTherm insulation. Furthermore a bespoke designed system eliminates any performance and design issues.

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