Wind Uplift Performance

The British Standard for Slating and Tiling, BS 5534, provides the construction industry with a primary source of guidance and recommendations relating to significant aspects of the design and installation of pitched roofing. BS 5534 advises on the design, performance and installation of pitched roofs and vertical cladding using slates, tiles, shingles and shakes and their associated components. It includes recommendations and guidance relating to the pitches, laps and details associated with different slating

and tiling systems; the selection and sizing of battens and counter battens; the methods of securing and fixing tiles and slates; and includes design recommendations for dealing with the critical structural loadings experienced by pitched roofing including recommendations and a proposed test method for assessing wind loading/uplift.

As a proactive manufacturer and supplier of a wide range of vapour permeable and high vapour resistance roofing and cladding underlays, Don & Low have undertaken a detailed testing and development programme to establish the implications of recent changes to BS 5534 on the installation and marketing of our underlay products. In particular, a comprehensive testing programme of underlays was undertaken following the method of testing and classification of roof underlays for wind uplift resistance (balloon test) given in BS 5534. All Don & Low products are fully compliant regarding the required product insert and third-party certification.

Wind uplift performance information is detailed on the product roll inserts. Roll inserts and installation instructions for specific products are also available for download.

Installing unsupported vapour permeable roofing underlays

Don & Low offer two installation options for their product range, providing designers and specifiers with a range of performance options to suit location and exposure. The options are as follows:

Un-taped overlaps: the underlay is laid across the rafters and fixed following the installation instructions; the overlapping joints remain un-taped.
Taped overlaps: the underlay is laid across the rafters and fixed following installation instructions; the overlapping joints of the underlay are taped using the membrane’s integral tape.

Taping overlaps provides additional resistance to wind uplift by reducing the risk of the underlay sliding below mechanical fastening, typically battens. RoofTX® CONSEAL underlays come with an integral tape. Complete installation instructions and performance information are provided within the appropriate Don & Low product inserts.

Additional performance information in other roof configurations

Counter Battens: There is no need to tape joints where counter battens are used. Where softwood boarding or timber sheeting is used below the underlay, counter battens are typically required to provide effective drainage below the battens. Where timber battens are positioned above the underlay, there is no need to tape overlaps to resist wind uplift. Independent testing has established that where counter battens are used, the wind uplift performance of the underlay (with untaped laps) exceeds the requirements of all UK wind zones.
Battens exceeding 25 mm: There is no need to tape joints where 38 mm battens are used. BS 5534 (Table 3) recommends minimum batten sizes for different applications, typically 25 mm deep. However, the structural designer may require deeper (38 mm) battens. Independent testing has established that, where deeper 38mm battens are used, the wind uplift performance of the underlay (with untaped laps) exceeds the requirements of all UK wind zones.
Slates Nailed Directly onto Sarking: There is no need to tape joints where natural slate is nailed directly into timber sarking. It is common practice in Scotland, and some rural areas of England, to nail natural slates directly to sarking or underlay boarding without battens/counter battens. Independent testing has established that where slates are fixed directly into timber sarking, the wind uplift performance of the underlay (with untaped laps) exceeds the requirements of all UK wind zones.

Information relating to the specific performance of each product in the above roofing configurations is present, along with the wind uplift zonal map, on the roll insert.

Accessories

Don & Low can supply a suitable double-sided overlap tape if required. Taping of overlaps should be undertaken following the installation instructions on the roll insert.