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BS 5534: A ridge too far for listed buildings?

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Geoff Wilkinson looks at the revised British Standard for roofing

As approved inspectors, we often get asked how to balance the requirements of Building Regulations against the practical issues of real life. BS 5534 is a classic case in point, with many Building Control bodies applying the requirements of the British Standard as if they were mandatory, causing significant issues, especially on aesthetic grounds when dealing with extensions to historic and listed buildings.

For those unaware, British Standard Code of Practice BS 5534 – slating and tiling for pitched roofs and vertical cladding was revised in 2014 and the changes took effect in 2015. 

Why was BS 5534 revised?

BSI recognised that global warming has resulted in increased frequency of extreme weather events such as gale-force winds, driving rain and flooding and that roofs were failing as a result. 

What are the key changes?

  • Mortar alone cannot be used to fix a roof’s ridges and hips. So, even if mortar is used, the ridges and hips must also be mechanically fixed;
  • Fixing requirements for roof tiles have been beefed up. All single-lapped tiles on a roof now have to be mechanically fixed and perimeter tiles must have a minimum of two fixings;
  • Lightweight underlays (as opposed to traditional bitumen-coated felt) can ‘balloon’ in the roof space, placing a load on the underside of the roof covering, with the potential to dislodge it. As a result there is now a new test for wind uplift resistance of underlays. 

These changes have caused a number of issues, as the design of a particular tile or ridge may mean it is impossible to apply the BS 5534 wind loading calculation methods to the particular design. 

In other cases, while it is possible to determine a theoretical wind loading on a product, it may be difficult – if not impossible – to find a practical or acceptably aesthetic way to fix the tile mechanically. 

In such circumstances a bit of common sense needs to be applied, as you are trying to match a product that has survived many years without failure. In most cases traditional roof tiles were not mechanically fixed at all, and generally relied on their weight, interlocking design or mortar to keep them in place.

As I have often stated before, the Building Regulations do not require compliance with a particular code of practice and in fact only require what is reasonable. In the front of the Approved Documents it clearly says that there may well be alternative ways of achieving compliance with the requirements and that there is no obligation to adopt any particular solution if you prefer to meet the relevant requirement in some other way.

In the case of roofing, an argument can be presented that the very fact that a traditional roof method has withstood the test of time proves that traditional methods are capable of being robustly installed, even if the installation method does not conform to modern installation requirements.

So, while installing to the British Standard isn’t a requirement by law, most third-party warranty providers will only cover a building if it has been installed to the relevant British Standards. 

Care also needs to be taken if reference is made (often inadvertently) within a specification to the need to comply with a particular standard. In practice, manufacturers providing products for the roofing industry, such as Wienerberger, Marley and so on, have some innovative products to help ensure you can follow the standard as far as possible and any deviation can be agreed with Building Control and documented to prove its suitability.

It is therefore important to speak to the building inspector during (or better still, prior) to submitting material samples under planning to make sure that the proposed solution is acceptable to all parties.

Geoff Wilkinson is managing director of Wilkinson Construction Consultants www.thebuildinginspector.org

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