Significant changes to BS8000-6
Many people in the roofing industry may be unaware that a revised version of BS8000-6, code of practice for slating and tiling of roofs and walls, was introduced at the end of September. This means that BS8000-6:1990 has now been superseded. Whilst this revised standard may not have attracted a great deal of attention, it does include some significant changes that roofing contractors need to be aware of.
The purpose of the code of practice is to encourage good workmanship and the recommendations apply to the laying and fixing of clay and concrete tiles, natural and fibre cement slates, and their associated fittings and accessories. Design aspects of slating and tiling are covered by BS5534:2003, which is itself under current revision and will be published in mid 2014, however the revisions to BS8000-6 reflect the future changes to BS5534, so the two standards can be used concurrently by designers and installers alike.
BS8000-6 was last published in 1990 and since then there have been some significant developments in the way that roof tiles are fixed, particularly as a high number of warranty claims has raised concerns about the performance issues of mortar. As a result, organisations such as the NFRC and NHBC have introduced new technical guidance on both the correct mix of mortar that should be used and the use of mechanical fixings with mortar bedded ridge and hip tiles. The new version of BS8000-6 now reflects this latest technical guidance as well as new health and safety legislation, so as a result there are some key areas that have been revised:
Health and safety
The revised BS8000-6 contains updated sitework practices to reflect new health and safety legislation, in particular the mechanical cutting of tiles and associated risk from silica dust.
The new code advises therefore that when cutting slates, tiles and fittings using a mechanical disc cutter, precautions should be taken to reduce the risk of dust by applying water during the cutting process, in accordance with the NFRC guidance sheet.
Preparation and application of mortar
Due to concerns about the performance and consistency of mortar, BS8000-6 now states that mortar for use in slating and tiling should be mixed in accordance with BS5534 and NFRC Technical Bulletin 27.
This means that roof mortar should be 1:3 cement: sand with plasticiser and the mix should be based on sharp sand with soft sand added to achieve workability with the proportion of sharp sand not be less than one-third of the total sand content.
The revised code of practice also emphasises that water should not be added to mortar which has become too dry to use, instead any leftover mortar should be discarded. The revised code of practice goes into more detail about the application of mortar and states that, wherever possible, the same colour and mix of mortar should be used for pointing as for the bedding and, when this isn’t possible, pointing should take place as soon as is practicable to ensure that the bedding and pointing mortar set as one piece.
It also states that the mortar bed should be of sufficient depth to compress when the slate or tile is fixed and firm enough to withstand the vibrations of nailing tiles, or the pressure applied as a result of mechanical fixings.
In line with current NHBC technical standards, the revised BS8000-6 introduces a new clause requiring contractors to mechanically fix all mortar bedded ridges, hips and verges, as well as tiles adjacent to valleys and abutments, in line with the future revisions to BS5534. This should be done either through a complete dry fix system or by using mortar bedding with additional mechanical fixings. It also recommends that all small tiles cuts should be mechanically fixed or bonded.
However, it does include an exception for historic or traditional roofing, where it states that ridge or hip mortar bedding may be specified without mechanical fixing.
The new version of BS8000-6 also includes updated clauses to reflect new recommendations for the use of roof underlays, the installation of roof slating and tiling battens and guidance on the installation of solar roof panels and accessories.
As with the previous version, the new BS8000-6 is a code of practice for good workmanship, not a legal requirement. However, we would urge all roofing contractors to adopt these new standards, as it will help them be prepared for the future fixing changes that are likely to be introduced in BS5534 next year. Although the detail is not clear at this stage, we know that this revised standard will involve changes aimed at improving the security of the roof structure, which could have significant implications for the fixing of roof tiles and slates, in particular concrete interlocking roof tiles.
The forthcoming revision to BS5534, which we know is closely allied to BS8000-6, is set to be in line with the Eurocode and is likely to result in more stringent roof tile fixing specifications nationally. This is primarily due to new wind loading calculations which take into account changing and future weather patterns. As a consequence, this is likely to impact on how the majority of pitched roofs are fixed in this country, as it is highly probable that all tiles would need to be mechanically fixed either with nails, clips or both.
The changes to BS8000-6 this September, along with those we will see next year in BS5534, are a clear indicator that with today’s extreme weather conditions, mortar bedding alone is no longer an acceptable method for fixing ridges, hips and verges. The increasingly stringent requirements to mechanically fix mortar bedded roof tiles mean that it is much simpler and just as cost effective to use a full dry fix system in the first place and we are likely to see a continuing shift towards these systems as fixing standards become tougher next year.