The fixing requirements for pitched tile or slate roofs have changed to recognise the increase in the incidences of extreme weather events. On 31st August 2014 the revised version was published of BS5534: The Code of Practice for Slating and Tiling.
The revised British Standard is designed to ensure that all UK roofs are more secure and that the materials used are suitable for purpose. There is a six month crossover period that means that from 1st March 2015 the new requirements will become mandatory.
There are three key areas to consider: the way in which tiles and slates are fixed; the end to using cement mortar alone as a means of fixing ridges and hip tiles and other fittings; and the requirement for testing and labelling of roofing underlays.
In the past when wind loading calculations have been used to determine the fixing specifications for tiles and slates the result on many roofs has been that only tiles in certain areas or perhaps in the 3rd, 4th, or even 5th course have needed to be fixed. In recent years the changes to theoretical wind loadings and the methodology used to work out fixing specifications has meant that increasingly the requirement has been for all tiles on many roofs to be fixed. The wind loading figures in the revised BS5534 will mean even more rigorous fixings are required.
All tiles and slates on virtually all roofs will now have to be mechanically fixed. Furthermore in most cases it will determined that clip fixings of a suitable strength material rather than nails will be required to secure the tiles. Additionally all tiles at roof perimeters, where there has always been a requirement for mechanical fixing, will now need a minimum of two fixings.
It is important for building owners, specifiers, and roofing contractors to understand these requirements and the impact they will have on costs, both in terms of additional materials and the time needed to fix the tiles or slates in order to comply with BS5534.
Ridge and Hip Tiles, and some other pitched roof fittings, have traditionally been bedded in cement mortar with the mortar alone relied upon as a means of fixing. This will need to change as the revised BS5534 states that cement mortar alone is no longer deemed sufficient to secure tiles and their associated fittings to the roof.
All Ridge and Hip tiles must now be mechanically fixed. Cement Mortar of the required mix can still be used but not as the sole means of fixing. The natural consequence of this will be the increased use of Dry Fix Systems which will ensure mechanical fixings and have the added benefit of being virtually maintenance-free. There will again be an additional material cost although in practice a part of this is offset against the increased speed of installation and the fact that they can be fixed even when frost or wet weather is expected.
There will of course be roofs, such as on heritage buildings, where dry fix products are not considered suitable. In these cases it will still be necessary to mechanically fix the ridge and hip tiles. This can be done by use screws with seals to fix them directly to the ridge or hip tree or supplementary timber batten. Most manufacturers should be able to supply pre-holed ridge and hip tiles for this purpose.
The increase in the use of lightweight roofing underlays in recent years has resulted in incidents of “ballooning” caused by wind deflection. This is where wind uplift on the underlay causes it to impose a load on the underside of the tiles or slates with the potential to dislodge them. This aspect of the performance of underlays has largely been unregulated in the UK and so the revised BS5534 has put in place mandatory requirements.
All underlays will now have to be tested to a uniform standard to ascertain their wind uplift resistance. The standard also gives guidance on any restrictions on the use of the underlay subject to aspects such as the building location, height of the roof, and the batten gauge that is to be used. The supplier of the underlay will then print a zonal classification label on the wrapping to provide information on its suitability.
In summary by working together all parties involved in the specification and installation of tile or slate roofs can ensure they are constructed and fixed in the correct manner. As independent consultants Under 1 can ensure that all your roofs are specified and installed to the highest standards. To get more information or to discuss your latest roofing project please contact us at firstname.lastname@example.org