How to reduce the weight of a flat roof construction

4 June 2021 Kingspan Insulation UK
Graph showing benefits of tapered insulation

Weight is an important consideration for any roofing project. By using lighter materials, it is not only simpler to get the roof up and installed, but also means structural requirements are reduced. This is especially important when refurbishing an existing warm deck flat roof construction where the cost of introducing extra structural supports may make the work impractical.   

Two commonly used ways of providing a fall on a flat roof are to either lay a cement: sand screed mix to a fall or to fit a tapered roof insulation system such as Kingspan Thermataper. The latter features tapered, hip and valley and flat insulation boards and are supported with a specialist design service to ensure they deliver the expected fall and thermal performance.

Learn more about tapered roofing and our tapered design service.

Currie & Brown have carried out research looking at how the use of these two approaches might affect the above deck weight of a warm deck flat roof construction. To do this, they selected four new build case study buildings with concrete roof decks. The buildings include 3 offices and a healthcare facility and feature roofs in a range of sizes and complexities. 

To ensure a fair comparison, the two build-ups are designed to achieve the same U-value of 0.16 W/m2K. The screed laid to falls option is insulated with Kingspan Thermaroof TR27, whilst the tapered insulation solution is Kingspan Thermataper TT47.

The approximate above deck weight for the two options across the different case studies is shown below.
Case study Roof Area (m2) Screed laid to falls build-up approx. weight (kg) Tapered insulation build-up approx. weight (kg)
1 192 42,000 1,000
2 338 73,000 2,000
3 3,073 1,005,000 23,000
4 1,512 389,000 11,000

The results show that by fitting a tapered roof insulation system, it is possible to make significant reductions in the overall weight of the above deck construction. This could help to avoid the need for additional structural or foundation work, saving costs. Further research has also shown that, in addition to these savings, the expected material and installation costs for tapered roof insulation is also as much as 30% lower than screed to fall approaches

Learn more about how tapered insulation systems can help to reduce costs.

From a practical perspective, the lightweight solution also makes it possible for the insulation layer to be fitted directly above the existing roof surface on certain refurbishment projects (where the existing waterproofing is in good condition).  This helps to cut down on installation time and, as it is fitted with a dry installation, no time is wasted waiting for the surface to dry. By comparison, screed to fall systems can take 200 days or more to dry in some cases. 

Learn more about how tapered insulation systems can speed up installations. 

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