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July 17 2019 Brunton's Blog
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Brunton’s Blog – Working with BS6229:2018
17/07/2019
Working with BS6229:2018
There are many important documents and standards in the construction industry, but to most of us none are more relevant than the updated and revamped BS6229 (2018 version). This has been with us since the end of last year and brings better focus and clarity than the previous standard.
During discussions recently with members it seemed clear to me that a brief review in the form of a blog might be useful on this key working document and the changes that it delivers. The new standard was necessary to reflect the changes over the last 15 years in our industry.
Much has already been written regarding the differences from the previous edition in this new version, but it does no harm to highlight the salient changes again. Continued reference and discussion regarding the new BS6229:2018 can only assist in embedding the concepts and very relevant information it contains, improving understanding, allowing better design and installation of flat roofs.
The first pleasant surprise for me was that the new document was less weighty than the previous version. It appears that various sections concerning metal roofs; copper, lead and zinc have been removed and the metal roofing industry now has responsibility for associated guidance. This, in my opinion, delivers a sharper, more focussed user-friendly document that can only assist in getting the required information across.
Also noticeable are clear recommendations regarding documentation to accompany any flat roofing project so accurate information regarding the design specification, as built details, product and system certification, maintenance requirements as well as details of all involved in the process to be held on file.
Terminology has had an overhaul and better definition of some terms. Key changes in terminology are as follows;
AVCL – Air and vapour control layer. This layer is now recognised for the role it plays in controlling air as well as the passage of vapour in roof build ups.
WFRL – Water flow reducing layer (used in inverted and some green roofs). This layer, placed on top of the insulation, reduces the quantity of water that flows to the roof waterproofing layer before entering into the drainage system. This improves thermal efficiency by reducing the amount of warm water runoff. As always it is important that the WFRL is installed correctly
Zero Falls – This term is defined in the new standard as a roof with a fall between zero and 1:80. For a ‘zero falls’ finished roof, a design fall of 1:80 should be used and analysis of the structure relating to construction process, loading, resulting deflection and settlement etc to avoid any back fall should be made. Only specific flat roof waterproofing systems have third party certification for type of design.
(Please Note: Design of falls guidance for flat roofs, in general (apart from zero falls) is also made clear indicating that all flat roof surfaces including gutters, should be designed to a fall of 1:40 to ensure finished roof surface falls of minimum 1:80 are achieved after construction process, loading, resulting deflection and settlement etc. takes place. The design should take account of all factors that impede proper drainage of the flat roof thereby reducing the risk of ponding).
Blue roofs– are referred to in the new standard for the first time, drawing attention to the attenuation capabilities of such designs from a flat roofing perspective.
Recommendations concerning warm, cold and inverted roof types.
The new BS6229:2018 makes clear recommendations concerning different types of flat roofs;
Warm roofs and inverted roofs are recommended; cold roofs are not recommended.
If a cold roof design cannot be avoided due to available upstand height for example, then adequate cross ventilation is required. The new standard sets out the relevant physical requirements for cross ventilation and should be consulted.
BS5250 is the ‘Code of practice for the control of condensation in buildings’ and clearly is a related reference document. This standard provides detailed information on condensation control and is currently being reviewed.
Inverted roofs
The WFRL, mentioned earlier, can have a significant negative impact on thermal performance of inverted roofs if it is not designed and installed correctly. The new BS6229:2018 recognises that further research and evidence is needed to correctly assess this effect. In the meantime, and until the standard is subject to a future update it recommends, to increase the design thickness of the thermal insulation by a minimum of 10% to mitigate any negative impact.
Flat roof upstands
Upstand height for detailing is a question that is still asked from time to time. An upstand height of minimum 150mm from the finished roof surface level is recommended by the new standard and this has proved to be sound advice, in practice, over many years. The finished roof surface level is at the top of any covering, for example stone ballast or paving that may be the finishing roof layer. An exception is made concerning the recommendation for access door thresholds on terraces and balconies where upstand height may be reduced to a minimum of 75mm. The new standard gives good specific information on these points.
The above are some of the key points regarding the new standard. There is plenty of other important information in the document that is not discussed in this blog. Therefore, I would recommend that all involved in flat roofing take the time to read and understand the new document BS6229:2018 as it can only be to their benefit. At SPRA we would always recommend reading our own SPRA Design Guide in addition to this. As mentioned in a previous blog we will be updating the Design Guide in the next few months in time for 2020. We will ensure to update or add any items from the new standard in the SPRA Design Guide for 2020 at that time.
Dr Ronan Brunton B.Sc MBA GMICE, Technical Manager