Lack of need for air gap makes revolutionary new Actis insulation ideal for headroom-critical projects

A revolutionary new insulation product designed to transform the loft and barn conversion sector can be used in roofs with shallow or uneven rafters and still deliver an excellent thermal performance - in part because its unique configuration means it doesn't require the usual 25mm air gap to avoid condensation for most locations throughout the UK.

The two-in-one reflective insulation and vapour barrier Actis Eolis HC, launched this month, combined with the 25mm gained through not needing the air gap, means it can be transformative.

The practice of not leaving an air gap is something of a radical move - with the standard requirement, under BS 5250, requiring such a gap where high resistance underlays such as sarking felt are used.

But the make-up of the Eolis HC and the configuration of the elements in the recommended build-up in a pitched roof means no such gap is required for most locations throughout the UK - and with every millimetre making a difference in a low headroom dwelling that could clinch the viability of a project.

Architect and Actis UK and Ireland technical director Thomas Wiedmer explained: "High resistance (HR) underlays usually require a 25mm ventilation gap on their warm side to avoid the risk of interstitial condensation, in accordance with BS 5250. Where ventilation of the air space is reduced, then a condensation risk analysis in line with EN 15026, such as a WUFI assessment, needs to be carried out.

"This dynamic simulation tool analyses the way heat and moisture move through a construction and can be used to assess the risk of moisture accumulation within any part of a roof build-up.

"The Fraunhofer Institute for Building Physics IBP carried out an assessment using its WUFI software, based on parameters deemed worst case scenario for UK applications.

"The assessment using WUFI software on the build-up in the illustration shown here concludes that over the simulation period of 30 years, there is no moisture accumulation in the assembly and that the water content of components is not critical from a building physics point of view, even without a ventilated air cavity between Eolis HC and HR underlay."

The results of the WUFI assessment, which takes into account all elements of the build-up along with weather data to generate its results, will demonstrate compliance in most locations within the UK.

Eolis HC will be especially transformative for loft and barn converters dealing with shallow rafters where headroom is at a premium. It removes the need to cut insulation between each rafter, with all the tricky and dusty cutting that entails if using PIR board, thanks to the fact that while it is thin enough to be used in low headspace zones it also offers excellent thermal performance.

Instead, they can just lay the product, like a blanket, across the rafters on the inside (warm side) of the building, sealing each section to the next with the self-adhesive lap feature of the product.

The Triplex technology on which Eolis HC is based is created from a number of layers of reflective films, each separated by a thin layer of fibre, trapping air between each section, thus boosting thermal performance.

Time trials show that when insulating a roof, installation time using Eolis HC is at least twice as quick as insulating between rafters with PIR board. The time difference is even more dramatically in favour of Eolis HC when taking into account the time taken handling materials on site and clearing up afterwards.

You can watch our step by step how to video here. And view our timed installation video demonstrating how quick and easy it is to install Eolis HC here.