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A big problem when designing an extension is what to do where the roof pitch is limited by existing windows or pipework. Using a matching natural slate or clay / concrete plain tile has always been out of the question but Klober’s new underlay, Permo® extreme RS SK2 can be used at 12.5° with profiled tiles or 15° with flat tiles and slates.
This provides complete flexibility with tile selection and avoids the need to use unsightly, large format concrete tiles which just weren’t designed for small roofs. Permo extreme is tear-resistant and has double, self-adhesive strips which provide a permanent seal of laps. It provides immediate weather protection, water driven to the top of tiles being carried between the counter battens to the gutter. This is a job that standard vapour permeable underlay are not designed to do.
Permo extreme is best laid onto 12mm ply board or OSB sarking board. This makes sealing laps easy and avoids the need for care when determining drape between rafters. Standard counter battening is employed with ventilation at or near the ridge with cold roof construction. Klober Butylon tape must also be used beneath counter battens to seal around any nail penetrations.