Why are insulation upstands used in flat roofing?
Following on from our earlier post on linear thermal bridges we are going to talk about a specific type of thermal bridge found on flat roofs and how this can be prevented by the use of insulation upstands.
The Accredited Construction Details (ACDs) include process sequences providing guidance on how to achieve good thermal continuity and air tightness. These are a standardised set of construction details, developed over a decade ago, to assist the construction industry in achieving the performance standards required to demonstrate compliance with the energy efficiency requirements of the Building Regulations / Standards, via a non-prescriptive route. They facilitate the ‘designing out’ of thermal bridges, while enabling the energy assessor to apply an approved psi value to each junction within the building at both the design and as-built stages.
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 which we’ve discussed previously.
The main reason for using these when insulating a roof is to prevent cold bridging at the junction between the roof and the exterior walls. A cold bridge occurs where there is a gap in the insulation, which may lead to condensation forming as this will be colder 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 entering at the edge of the roof.
Generally we recommend that there should be a minimum distance of 300mm maintained between the top of the insulation upstand and the bottom of the horizontal roof insulation. A 25mm thick Kingspan Thermaroof TR27 LPC/FM upstand should be used around the perimeter of the roof on the internal façade of parapets. The only exception is Styrozone flat roofs where we recommend using Purlcrete as the upstand. It there is a cavity insulation board in the parapet, this should be taken up as high as the flat roof insulation upstand to prevent cold bridging through this.
If you want more information our Roofing quick guide goes into more details about installing flat roof insulation.
Share this blog post with your friends and colleagues by clicking on the social media icons below.