What specification considerations relating to BS 5534
The revised British Standard for pitched roofing, BS5534, Slating and tiling for pitched roofs and vertical tiling – Code of practice, came into effect on the 31st August 2014 and will run alongside BS 5534:2003 + A.1:2010 until it is withdrawn at the end of February 2015. What are the changes to the standard and the impact of them?
The latest changes to BS5534 are more than a simple update; they reflect improvements to working practices and introduce some fundamental changes to product selection. The revisions also go some way to address the correct certification of products; this will continue to raise the standards within the industry.
The new BS5534 is intended to be read and used in conjunction with BS8000-6: 2013 Workmanship on Building Sites – Part 6: Code of practice for slating and tiling of roofs and walls, and BS5250 Code of practice for Control of condensation in buildings. These standards often cross reference with BS5534 being centred on design and BS8000 on workmanship. In some instances NFRC Technical Bulletins are referenced usually for information with the exception of TB34, Wooden Shingles and Shakes which is normative (i.e. must be complied with).
The changes to BS5534 address new methods of calculating wind loadings on buildings, as expressed in the relevant Eurocodes for the basis of structural design, resulting in an increase in the number of fixings required for some types of roof coverings. It also addresses vulnerable areas of the roof where there have been failures.
The main elements of change are:
- Fixing specifications: The new method of calculating wind speed has resulted in increased specifications. For example, all single lap tiles must be either full fixed, all nailed, nailed and clipped in some area or nailed and clipped. There are also changes to slates and plain tiles too.
- Underlays: new testing and issues concerning both drape and possible ballooning.
- Battens: must meet the requirements in the standard. That is, batten now must be graded to BS5534.
- Mortar: Mortar is now deemed to have no tensile strength so that areas where it is used, such as at hips, ridges, verges and valleys, all associated components must be mechanically fixed.
So that’s the theory… but how does it affect roofing specification and product selection?
We speak to John Dodd, roofing consultant and Chairman of the BSI committee B/542/1 that drafted the revised BS5534 standard, to find out how the changes impact specification:
Specifiers embarking on the design of pitched roofs and the specification of discontinuously laid roofing products – tiles, slates and shingles – will now have to consider the impact of a raft of changes as listed below:
- Harmonised technical specifications and a manufacturer’s declaration of performance as part of the European Construction Product Regulation rules (CE marking) or Third Party accreditation;
- More stringent fixing specifications for tiles and slates as a result of the adoption of Eurocodes for the calculation of wind loads;
- Grading of timber battens to meet enhanced levels of strength and durability;
- Classification of roof underlays related to their wind uplift resistance and scope of application;
- Revised and updated specifications for board and sheet sarking materials and roof decks;
- Headlap and sidelap calculations for double –lap slates to ensure effective weathertightness at minimum roof pitches in all exposure conditions;
- Mechanical fixing of mortar bedded roofing components as result of no longer being able to take account of any tensile bond strength of the mortar;
- Revised guidance on roof drainage and the application of flashings and weatherings;
- Increased importance of the durability factors that affect products and their fixings;
- Complementary recommendations for the design of roof details in terms of both design and workmanship (BS 8000-6) and the control of condensation (BS 5250).
The new standard has also been updated to reflect changes in product standardisation, the introduction of new and proprietary products, such as dry fix systems which eliminate the need to use mortar. The specifier of such products should still however seek assurance from the manufacturer that the product either has independent UKAS approved Third Party assessment or similar test evidence based on UK conditions of use. BS5534 makes specific reference to the marking of timber battens ‘BS5534’ which represents a manufacturer’s declaration of conformity and is not to be confused with a third party certification of conformity, which is independently assessed.
The latest revision to BS5534 also comes at a time when the specification process of construction products is undergoing a radical change with introduction of new technology and the adoption of BIM (Building Information Modelling). Some manufacturers have already reacted and have produced BIM data for their products, in addition to the introduction of new ‘on-line’ apps and specification tools which will calculate fixing specifications, produce NBS specifications and calculate quantities of materials.
During the first few months of its introduction, feedback from the roofing industry is that the new changes to BS5534 will inevitably increase costs, both in terms of labour and materials. However, with a recent track record of failing standards and performance in pitched roofs, the new changes will herald overall long- term cost savings by improving the performance of tiled and slated pitched roofs in the future.