Why are insulation upstands used in flat roofing?

inverted roof

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.

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Kingspan Insulation is a market leading manufacturer of optimum, premium and high performance rigid insulation products and insulated systems for building fabric and building services applications.

0 comments on “Why are insulation upstands used in flat roofing?
  1. Hi,
    We are building a thin (1.3M x 8M) single storey ground floor extension on to the front of our house. This will have a flat roof and hopefully contain skylights and an up-stand to give the extension a flat front with a stone capping. this extension will also in part, run alongside another flat roof which is constructed as a balcony.
    I have spoke to your helpline about your OPTIM-R insulation in an attempt to reduce some of the thickness of the insulation.
    Are there any alternative methods or products that may help reduce the height of the up-stand and deal with the thermal bridging of the perimeter cavity wall?
    Thanks,
    Wayne Frost

    • Hi Wayne

      Kingspan OPTIM-R will ultimately be the thinnest solution for a warm roof application. You could also consider a hybrid flat roof, where a small amount if insulation is underneath the roof deck and the rest is over the top of the roof deck – this will need to be discussed with our technical department as we will need to run a project specific condensation risk analysis. A third option is to construct a cold flat roof. This is a roof where all of the insulation is installed underneath the rood deck, with a 50 mm fully ventilated air space running between the underside of the roof deck and the top of the insulation. The ventilated airspace stops condensation build-up on the underside of the roof deck.

      In any case, we recommend you continue liaising with our technical department on 01544 387 382. They will help you find the best option for your application.

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