The revision to BS 5534 aims to improve roof security

The code of practice for slating and tiling (BS5534) is being revised later this year, incorporating a number of changes with the aim of improving the overall security of the roof and reducing the chance of damage in the face of increasingly extreme weather events. Gavin White, product manager at Marley Eternit, outlines the proposed changes and discusses how this will impact on the way pitched roofs are fixed in the UK.

Increasingly volatile and unpredictable weather conditions in the UK over the past few years have exposed the vulnerability of mortar as a method of securing roof tiles and fittings.  There are also questions about the adequacy of current fixings specifications for roof tiles as well as issues relating to lightweight underlays and their vulnerability to wind deflection.  Therefore, as experts predict that we are likely to experience more extreme weather events over the next 25 years, industry standards are being revised to increase the overall security of the roof.

What are the changes?

It is now widely agreed that ridge, hip and verge tiles bedded with mortar are more likely to become displaced due to strong winds, unless they are also mechanically fixed using screws, clips or nails.  The NHBC introduced its own regulations two years ago, which means that it now requires all homes that it guarantees to have mechanically fixed ridges and hips – either through a complete dry fix system or using mortar bedding with additional mechanical fixings.  Now BS5534, the code of practice for slating and tiling, is also being revised in line with the NHBC guidance.

When it comes to securing the roof structure, mortar will no longer be deemed as sufficient in strength to provide a sole means of securing ridge and hip tiles, or verges and valleys.   At the moment BS5534  already requires a degree of mechanical fixing, for example the two end ridge tiles and any other tile that ends a run of ridge tiles, e.g. around a chimney, must be mechanically fixed to protect against wind damage.  However, under the revised standard, it is likely that any mortar bedding will have to be accompanied by a mechanical fix, either through a complete dry fix system or using additional fixings with the mortar.

The revisions to BS5534 are also likely to lead to more stringent roof tile fixing specifications, which could impact on how the majority of pitched roofs are fixed in this country.  Although the details are not confirmed at this stage, we do know that the revised standard is set to be in line with the Eurocode and is likely to result in a number of changes.  BS5534 will use new wind loading calculations which take into account changing and future weather patterns.  This means that whether builders and roofers get fixing specifications via the Zonal method, or direct from the manufacturer, there will be a general increase in the amount of tiles that have to be nailed and / or clipped. 

In addition, there are also likely to be changes in the new revision in relation to the securing of underlays following  a number of issues with some of the new lighter weight products being subjected to wind deflection, causing  ‘tenting’ in the roof cavity.  This has often been made worse by excessively draped underlay which has lifted and in some instances actually dislodged the roof tiles or slates above. 

Originally we were expecting the new BS5534 to be introduced around April 2014, although there are some indications that this may be slightly delayed.  However, there are some changes that industry could be making now in preparation for the changes.

  • If you’re not already doing so, consider using complete dry fix systems for securing ridges, hips, verges and valleys.  These not only provide a mortar and maintenance free method of mechanical fix but in the case of dry ridge and hip systems, like those offered by Marley Eternit, also provide sufficient ventilation to meet the requirements of BS5250
  • If dry fix isn’t an option, make sure you use additional fixings for any mortar bedded tiles.  Not only will this get you ready for the changes but will also protect the quality of your own work. Mortar bedding ridges and hips, without any additional fastenings, could lead to claims against your own guarantees in the event of mortar failure 
  • Remember that there is a mechanical fixing kit available for mortar bedded systems that Marley Eternit launched last year which is accompanied by purpose made clips for securing small tile cuts
  • If you are using mechanical fixings with mortar, don’t forget to ensure there is adequate high level ventilation as unlike many dry fix systems, mechanically fixing mortar bedded ridges and hips does not provide the required ventilation at high level or in the roof void, which is required for the majority of pitched roof designs
  • If you need advice or further information, contact our technical team on 01283 722588

While the changes to the standard may seem like an inconvenience, it is important to realise that there has been a rising number of roof claims due to the failure of mortar and the revised BS5534 is trying to reduce the possibility of roof damage in the face of increasingly extreme weather events.  The fact that the standard is changing supports those builders and roofers who have been trying to encourage the use of mechanical fixing among their customers and enables them to offer a more secure option and add value to sales.  

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