Kingspan Guest Blog – Minimising Heat Loss through Flat Roofing

A warm flat roof is the easiest way to minimise heat loss

A warm flat roof is where all the insulation is applied above the deck, with the waterproofing layer installed on top. This method ensures the entire roof is wrapped in insulation, offering the best thermal performance for the least amount of product.

This is the opposite of a cold flat roof, where all the insulation sits either within or below the roof deck. This causes a high rate of heat loss, leaving the deck at the same temperature as its surroundings.

Choosing the best product for a warm flat roof

Kingspan Thermaroof TR26 LPC/FM and Kingspan Thermaroof TR27 LPC/FM are both suitable for a warm flat roof.

Thermaroof TR26 is designed for flat roofs with a waterproofing layer that needs to be mechanically fixed. Faced on both sides with a low emissivity foil facing, it offers a better thermal conductivity than Thermaroof TR27, but you will need to ensure use of telescopic tube fasteners, rather than any standard fasteners, in order for it to perform its best.

Thermaroof TR26 is particularly suitable for windy areas, where the insulation must be mechanically fixed through the insulation into the deck to avoid wind uplift. However there are situations where this method of fixing is not suitable. This is where Thermaroof TR27 can be used.

Thermaroof TR27 is faced on both sides with a coated glass tissue facing. It is suitable for a range of waterproofing systems including; fully adhered single-ply, partially bonded built-up felt, mastic asphalt or cold liquid membranes.

The importance of good workmanship

When using either Thermaroof TR26 or Thermaroof TR27, the product must be correctly installed in order to limit heat loss. This is where the junction detailing between the roof and other elements becomes important.

For example, any parapets should have the wall insulation taken up past the roof deck insulation. This should result in far less heat loss than a standard flat roof junction. Combine this with an upstand of either Thermaroof TR26 or Thermaroof TR27 (to match the product you’ve used over the deck itself), and you will retain more heat than you would with a standard flat roof.CCF can supply both of these products and accompanying products alongside know-how and friendly service at your local branch. For further information please use the branch finder to contact your local depot.

Further advice on how to minimise heat loss can be found within the Kingspan Thermaroof TR26 LPC/FM and Kingspan Thermaroof TR27 LPC/FM product literature. The Kingspan U-Value Calculator will also come in handy when determining what thickness of insulation you need for your project.


Without a parapet this junction would achieve a psi-value of between 0.24 and 0.31W/m.K, depending on the block work.

Junction without parapet   Junction without parapet

With a parapet, and its insulation taken up above the flat roof insulation, this junction would
achieve a psi-value of between 0.06 and 0.20 W/m.K – again depending on the block work.

Junction with parapet 2  Junction with parapet 2

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