At the end of August the British Standard for Slating and Tiling (BS 5534) was updated to incorporate a range of changes with the aim of improving the overall security of the roof structure. The purpose of the revision has been to bring the UK in line with European standards (Eurocodes) and also to ensure that the future roofscape is better prepared for increasingly hostile weather.
Representing the most significant change to roofing standards for over a generation, it is vitally important that all in the roofing industry, including specifiers, merchants and contractors alike, are fully up to speed on what the key changes are and what they will mean for their business.
The three main areas of change focus on:
- Mechanical fixing for mortar bedding
- Tile fixing
Mechanical fixing for mortar bedding
Whilst mortar bedding has traditionally been a popular means of securing verge tiles and other roof fittings, the revised British Standard now states that this method is no longer sufficient on its own. Importantly, mortar bedding is still permitted, but must now be accompanied by a mechanical fixing. There are also new guidelines to ensure the formation of a suitable roofing mortar, using the correct sand and cement mix. This has been included to help resist problems traditionally associated with mortar, such as cracking caused by shrinkage and building movement.
In the long term, it is expected that this change will further drive the industry towards using dry-fix systems, which not only provide a mortar free means of mechanically fixing, but in the case of some dry ridge and hip systems, can also assist with ventilation towards the requirements of BS 5250 (control of condensation).
Manufacturer’s fixing specifications have traditionally taken into account a number of factors when calculating the bespoke fixing requirement for a roof. The basis of these fixing specifications come from calculations within the British Standard that combine factors such as wind uplift in conjunction with tile weight and resistance from fixings.
Previously, fixing specifications have ranged from perimeters nailed in sheltered areas through to every tile clipped in areas of high exposure. However, changes to the calculations in the new standard will mean that, at a minimum, all single lap tiles will have to be mechanically fixed with either nails or clips and the proportion of each will vary dependent on factors including location, pitch and product.
The issue of underlay “ballooning”, and its consequences for the roof has become an increasing occurrence over recent years, specifically with the introduction of new lighter weight products. Wind deflection within the roof space can, under the right conditions, cause the underlay to lift up, and place a load on the underside of the roof covering, and in some cases dislodge it. The new standard has attempted to address this issue by introducing new fixing requirements for underlays with measures including the securing of laps with a naturally occurring batten course.
In addition, the standard also introduces a new test that measures the ability of an underlay to resist stretching when exposed to wind pressure. These test results are then used to establish which types of underlay are suitable for the various regions around the UK.
These changes are a significant step forward from what has been the baseline standard for roofing practice in the UK. As a result all tile manufacturers are revising their technical advice in line with the new Code of Practice, please see RTA members’ individual websites for product-specific information.