This post describes the specific type of thermal bridge found on flat roofs and how this can be prevented by the use of insulation upstands.
For flat roofs, we suggest the use of insulation upstands to prevent thermal bridging. These are small sections of insulation which are positioned vertically around the edges of some constructions of flat roofs. This is similar to the upstands used in concrete floor insulation.
The main reason for using these when insulating a roof is to prevent thermal bridging at the junction between the roof and the exterior walls. A thermal bridge occurs where there is a gap in the insulation, which may lead to condensation forming as this will be hotter than the main part of the roof. It is important to minimise this wherever possible. This can be done by using insulation upstands. The waterproofing layer also has to be taken up the parapet to prevent water from entering at the edge of the roof.
Guidance
Generally we recommend that there should be a minimum distance of 300 mm maintained between the top of the insulation upstand and the bottom of the horizontal roof insulation. A 25 mm thick Kingspan Therma TR27 upstand should be used around the perimeter of the roof on the internal façade of parapets. If there is a cavity insulation board in the parapet, this should be taken up as high as the flat roof insulation upstand to prevent thermal bridging through this.