High performance XPS

For over 30 years the design of flat roof systems in new construction has been driven by the availability of low Lambda value, high thermal performance Polyurethane (PUR) and later Polyisocyanurate (PIR) insulation boards. The reason is simple; they offer a roof construction that is thin to achieve a given U-value.  As U-values have got ever higher (but numerically lower) achieving the desired design thermal performance has resulted in PIR insulation thicknesses over tripling (from a typical 50mm on the 1980’s to 150mm in the 2000’s).

This low Lambda per 10mm thickness has helped the warm roof become the default design for many architects, enabling them to minimise the thickness of the roof zone and maintain internal ceiling heights, even with the 0.15 Wm2/k U-value target or better.

Whilst this drive has undoubtedly been positive for the roofing industry, the thermal performance of buildings and the energy bills of building owners, there are applications where a warm roof construction is not the ideal scenario from either a construction or use perspective. Applications such as podiums, terraces, high traffic areas or plant areas with high loads are not best suited to a warm roof installation using a PIR insulation board.  

In these applications an inverted roof can provide a build-up more suited to the construction and use phases of the building, but this has always been at the penalty of a thicker roof zone build-up which will not always fit within the architectural intent (let’s not discuss ‘architectural intent’ and the real-world conflict!).

High performance Extruded Polystyrene (XPS) offers an insulation solution that comes closer to the thickness of PIR insulation boards without the cost penalty of a Vacuum Insulated Panel (VIP); and the good news is that RAVAGO Building Solutions Ravatherm XPS X ULTRA 300 SL is back in production after a brief pause due to non-availability of the unique blowing agent used to make the insulation.

What’s so special about Ravatherm XPS X ULTRA 300 SL I hear you ask? How does a Design Lambda value over 25% lower than the most common XPS Declared value sound?  Translate that into thickness for a target U-value and for a 0.18 W/m2K the ‘ULTRA’ will be 145mm vs 190mm. For 0.10 W/m2K the ‘ULTRA’ will be 260mm vs 360mm, but will also achieve that in two board thickness versus three for the common XPS (some need four board). The cost savings in terms of installation, transport, cranage and carbon emissions are significant. Oh, and it’s BBA Certified too.

At QI we welcome the return of an innovative and market leading product that helps the Roofing Industry deliver better solutions for its clients.

Next month: UKCA marking, what is it and do we need it?