Tests at the BRE’s Garston laboratories have proved that Klober’s Permo Extreme roofing underlay can withstand the rigours of the UK’s weather without the need for support boards beneath it. This will mean that roofing contractors can make significant savings in time and materials.
Graham Copson, Klober’s Technical Manager, estimates that removing the need for plywood or OSB boards and counter battens will save at least £8 per m2. It will also save on labour costs, and remove the safety risks associated with lifting and laying boards.
“The way Permo Extreme performed in the tests underlines what a premium product this is,” says Graham. “There was no leakage, even at the most extreme conditions”.
Permo Extreme is a tear-resistant underlay, designed for use on low pitched roofs. It can be used at 12.5o or more for profile tiles, 15 o for slates and 22.5 o for plain tiles. Introduced in the UK in January 2013, it is made from robust PES (polyethersulphone) fleece which allows vapour to escape, while keeping rain water out.
In the BRE tests, Permo Extreme was laid at 12.50 with no slates or tiles on top of it and a 10-to-15mm deep drape – or sag – between rafters, in line with the latest update to BS 5534, the code of practice for slating and tiling for pitched roofs and vertical cladding. The underlay was fastened to the rafters with tacks and 50mm Butylon tape fixed down the rafters to seal around any nail penetrations. Battens were installed with fixing nails through the Butylon tape and the next layer of Permo Extreme laid with a 100mm headlap so adhesive strips meet.
The first test was a rain deluge test designed to create one-in-fifty-year conditions. The second combined wind, driving rain and suction from underneath, with all three elements increasing every five minutes over a 55-minute period, again mimicking one-in-fifty-year conditions.
The Permo Extreme was tested at over 110 Pascals, which is an impressive achievement according to Graham. “To give an idea of what that means, most interlocking tiles start to leak at between 25 and 30 Pascals, so it performs far better than interlocking tiles”, he explains.
Klober has updated its data sheets and installation instructions to reflect the results of the latest tests. Says Graham: “It’s good news for everyone: building owners, contractors and hopefully us too.”
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