Permo® extreme RS SK² from Klober – Europe’s leading manufacturer of high-performance roofing membranes, ventilation and accessories – is a waterproof, tear-resistant underlay, designed for use on low pitched roofs.
Suitable for profile tiles pitched at 12.5o or more, 15o for slates and 22.5o for plain tiles; it is manufactured from a bondable two-layered underlay with a shrink-resistant TPU coating on a robust PES (polyethersulphone) fleece which allows vapour to escape, while keeping rain water out. This high performing underlay is now available in a smaller roll size of 37.5m².
Double self-adhesive edge strips provide a permanent seal and immediate weatherproofing against wind, rain and snow; while the PES fleece also incorporates a capillary stop to control the formation of condensation. This means that, unlike traditional vapour permeable underlays which provide limited weather protection if left, Permo® extreme can provide a temporary weatherproofing layer if required.
With a high-temperature stability that peaks at 100°C and due to the fact that it is very UV-resistant, it also means that Permo® extreme is highly suitable for installation under in-roof system solar panels.
Another benefit of Permo® extreme is that it dispenses with the need for plywood or OSB support boards and counter battens – which the company estimates saves at least £8 per m2 in materials at least, not to mention time and labour costs.
This ability to self-support was established through in-depth testing at the Building Research Establishment (BRE). In the BRE tests, Permo® extreme RS SK2 was laid at 12.5o with no slates or tiles on top of it and a 10-to-15mm deep drape between rafters, in line with the current version of BS 5534. The underlay was fastened with tacks and 50mm Butylon® tape fixed down the rafters to seal any penetrations. Battens were installed with fixing nails through the tape and the next layer of Permo® extreme laid with a 100mm headlap so adhesive strips met.
The first test was a rain deluge designed to create a one-in-fifty-year condition. The second combined wind, rain and suction from underneath, with all three elements increasing every five minutes over a 55-minute period, again mimicking a one-in-fifty-year condition.
For context, most interlocking tiles start to leak at between 25 and 30 Pascals, while Permo® extreme was tested at over 110 Pascals – without any water ingress at all.
It’s also the ideal choice for those seeking a bondable underlay for a rainproof sub-roof. Not only is it tear-resistant, highly weatherproof and avoids the need for sarking boards, it also – when laid as a key primary barrier with its associated accessories – comes with a 10-year guarantee providing that it has been installed in accordance with Klober’s installation instructions.
Permo® extreme RS SK2 is complemented by a range of accessories such as Permo® extreme sealant which allows connection to rising structural components and eave flashings; an EPDM sealing collar suitable for the sealing of pipe penetrations; and Butylon® tape, which is ideal for creating seals around nail penetrations.
Permo® extreme RS SK² is available in sizes 50 x 1.5m (75m²) 18kg, and 25 x 1.5m (37.5m²) 9kg.