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Wind Damage to Tiled Roofs by Chris Thomas

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During the recent periods of bad weather across the UK, high winds have caused damage to roofs. This has left some home owners feeling the need to form local pressure groups to persuade their Builders to not only repair their roofs, but to do so in such a manner as to ensure that roof damage does not happen again to their principle investment. They are citing in their defence that the roofs were not fixed correctly in the first instance. Picture 1
Since the introduction of BS 5534 the code of practice for slating and tiling in 1978 there has been a calculation method to determine the minimum-fixing requirement for every roof in the United Kingdom.
Compliance with the tile fixing requirements of BS5534 will automatically ensures compliance with BS8000 The code of practice for workmanship on building sites: part 6 Slating and Tiling, which in turn will comply with the requirements of regulation 7 of the Building Regulations.
The National House Builders Council (NHBC) provides recommendations for every aspect of house construction in its technical manual. Table 2 of Appendix 7.2-C of the NHBC technical manual gives minimum fixing recommendations for single-lap interlocking concrete tiles. Table 3 gives the minimum fixing for plain, double lap tiles with nibs.
Table 2 states that the end tile in each tile course at a verge, abutment, valley and hip must be nailed or clipped, also every tile in the first course at eaves and top edges (ridge) must be nailed or clipped. In many cases this table has been interpreted as the fixing recommendation for all houses within the NHBC scheme. Many builders miss the note underneath stating "Additional nails and clips may be required depending on pitch and degree of exposure. Following the manufacturer's recommendation. Evidence of calculations in compliance with Technical Requirement R5 may be required". This is often interpreted as being optional rather than a mandatory requirement. The statement also avoids any reference to compliance with BS5534 that is mentioned earlier in the NHBC technical manual. However by seeking a manufacturers recommendation, they should be in compliance with BS5534 fixing recommendations.
Table 3 is more definitive with regard to the fixing of tiles in the general area, a term not clearly explained. It states that up to 60 degree (rafter pitch) the tiles are to be fixed with 2 nails per tile every fifth course. Over 60 degrees the tiles are to be fixed with 2 nails per tile in every course. There is no additional note as with table two relating to further fixing, obtaining a manufacturers recommendation, or any reference to compliance BS 5534. Whilst the over 60 degree statement does agree with BS5534, below 60 degrees it only complies in low wind uplift situations.
Whilst the NHBC technical manual seeks to simplify the requirements of roof tile fixings, it would appear that for some roofs have passed the NHBC final inspection with roof tiles that are not adequately fixed to comply with Regulation 7 of the building Regulations.
During the recent period of bad weather that affected most of the UK, the estates of houses built by NHBC registered Builders, that have incurred damage to roofs have not experienced winds that have exceeded the wind speeds that could be expected to occur at least once in any 50 year period for that locality. The 50-year period is a standard period that is used in the fixing calculation method in BS5534. On an initial review of the problems, it would appear that all the affected roofs were not fixed using the manufacturer's recommendations and calculations may not have been done prior to the roof being tiled.
If this is the case, the long-term implications could mean that many more house owners have a strong claim against their NHBC backed guarantee. Having had the roof tile fixing issue brought to their attention, the NHBC may respond by increasing, or clarifying the tile fixing specification and inspection for all future roofs. The likely consequence of this discovery may be an increase in the cost of roof construction by an average of 300 per house. This would cover the extra roof fixings and any increase in the NHBC guarantee premium to pay for the claims that may result from tile fixing problem dating back over the last ten years.
The NHBC, and/or the house builders, may try to deflect blame for the problem back to the tile manufacturers. However, there is sufficient documentary evidence to show that during the hurricane force winds that occurred in 1987 across the South East (a once in 200 year event), in exposed locations in Cornwall, South Wales and the western isles of Scotland, tiled roofs fixed in accordance with BS 5534 have not sustained damage. However incorrectly fixed roofs have sustained damage.
The major roof tile manufacturers all provide a means of obtaining safe fixing specifications for their products. In most cases this service is free and the calculation is undertaken from the answers to approximately 20 questions related to the site and the building. There is no reason why any tiled roof should not be fixed correctly given the knowledge contained within the British Standards, the fixing specification calculation services provided by manufacturers and the notes contained in the NHBC technical manual.
The adoption of the recommendations contained within BS5534 and BS 8000 part 6, as promoted by the Government and Insurance industry initiative, the Roofing Hallmark Scheme, could reduce the long-term claims on the insurance industry, including the NHBC. Especially as scientists are informing us that periods of high winds will occur more frequently with the changes that are predicted in the global climate.
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