By John Mercer, Technical Manager at Sandtoft, a Wienerberger brand
BS 5534: 2014; the revised British Standard for slating and tiling was published in August this year. This represents some of the most wide-ranging and fundamental changes to UK roofing practice that we have seen in a long time. In future, every ridge and hip tile on every roof will require mechanical fixing and more fixings will be required for the general tiles and slates. At long last the long-standing problems of mortared ridges and roof tiles generally being under-fixed should now become a thing of the past and the industry will have clear guidance on the use of suitable underlays.
Sandtoft will be offering training courses to the industry on the changes to the roofing Standard.
The pitched roofing industry has six months to make the necessary changes in products, specifications and working practices to comply with the new requirements.
John Mercer reports:
Firstly, I will reiterate what the three main changes to the Standard are: -
1. Until this point, underlay has, to a large extent, been unregulated in the UK, meaning that even the thinnest, lightest material could potentially be used, unsupported, on pitched roofs. Now, there is a test method to ascertain the wind uplift resistance of the underlay, bearing in mind that the underlay carries a major proportion of the wind load on a tiled or slated roof. The Standard also gives guidance on restrictions on the use of underlays, such as maximum batten gauges and country zonal areas.
2. Mortar bedding will no longer be relied on as a fixing. Mortar can still be used, but it must be supplemented with mechanical fixings such as nails, screws or clips etc. In practice, this means that mortar bedded ridge and hip tiles must all be mechanically fixed.
3. Theoretical wind loadings on the roof have increased. This means that stronger and more fixings are required to secure the roof tiles and slates. In practice, it is unlikely that any roof tiles on a roof would not require fixings.
So what implications do these changes have for the roofing contractor?
With regards to the underlay, the supplier will print a zonal classification table on the underlay wrapping label. This will provide the user with information on geographical zone suitability and maximum recommended batten spacings. So, for example, an underlay with a measured wind uplift resistance of not less than 1900 N/m2 can be used in all UK zones at batten gauges up to 345mm. This can be reduced to 1600 N/m2 in buildings that have well-sealed ceilings. There are limiting factors within these recommendations; for example, the ridge height must not be greater than 15 metres, or the site altitude must not be greater than 100 metres and the site topography is not classed as ‘significant’. Where a site is outside these conditions, a calculation is required to determine the required wind uplift resistance of an underlay. The roofer should request this from the underlay supplier.
To comply with the new requirement to mechanically fix ridge and hip tiles, the obvious solution is to use dry fix systems. These offer the installer many advantages that are well understood, such as speed and ease of installation, the ability to work without worrying about the imminence of frost or rainfall etc., as well advantages within a roof system, such as the provision of roofspace ventilation and the ability to cope with structural movement etc. However, there are circumstances where it is still appropriate to use mortar bedding; for example on heritage work and for roofing tiles such as traditional clay pantiles or handcrafted clay plain tiles. The easiest way to mechanically fix a ridge tile is to use ridges that are pre-holed by the manufacturer and use screws with sealing washers to secure each ridge tile to the ridge or hip batten. On trussed roofs, where there is no ridge tree, a timber ridge batten can be secured to the apex using suitable straps or brackets. Seek advice on suitable mechanically fixed mortared ridge and hip details from the roof tile manufacturer.
Perhaps the change that will have the greatest impact on the roofing contractor, though, will be the higher theoretical wind loads that will mean greater and more tile fixings. Because most, if not all, roof tiles will now require fixing, the roofer will need to find different ways of working to avoid foot traffic across laid roof tiles. Gone are the days when the roofer could push unfixed tiles up to expose the tile battens to walk on.
Roofing tiling will need to be treated more like slating, where the need to avoid walking on laid slates is well understood. Tiling should be planned so that as work progresses roofers can work off battens as much as possible. Where working over areas of laid tiles is unavoidable, the tiling should be protected using crawling boards etc, with suitable packing between the boards and the tiling. Tile manufacturers will provide method statements for replacing individual broken tiles, but this is only intended for the occasional damaged tile and not areas of tiles broken through foot traffic.
Look out for underlay with a geographical zonal table printed on the label and only use an underlay that is classed as suitable for the location and tile batten gauge.
Mechanically fix all ridge and hip tiles. Generally, this is most easily done using dry fix systems, but ask your roof tile manufacturer for an appropriate detail when mortar bedding.
In future all tiles will be mechanically fixed. Therefore, plan your work to accommodate the extra time needed and avoid or at least minimise foot traffic over laid areas of tiles. Where necessary protect the tiles using crawling boards or roof ladders.