In the first of a two-part feature, Dr Kevin Ley, Technical Manager of Redland, explains how site practice is still lagging behind the British Standard Code of Practice for Slating and Tiling (BS 5534) coming into full force; and resulting in void warranties and, worse, significant roof failures.
The first version of BS 5534, the Code of Practice for Slating and Tiling in the UK was CP 142, published in September 1942.
It set the standards for recommended best practice for slating and tiling, covering all aspects of pitched roofing above the rafters. It was first set as a British Standard in 1978 and has been updated on a number of occasions since.
Most recently revised in August 2014, significant changes included the introduction of mechanical fixing of all hips and ridge tiles, new wind uplift resistance requirements for underlays; and a considerable increase in the tile fixings particularly for interlocking tiles which are the most widely used.
In the latter, this increase has been brought about by a simultaneous increase in the minimum tile fixings required for tile security and safety along with increased design wind loads, by up to 100% in some cases. Consequently, all single lapped, interlocking tiles on a roof now need to be nailed, clipped or both depending on exposure
BS 5534:2014 applies to all pitched roofing, whether new build, re-roofing or repair work, and came into full force in March 2015. Although not legally mandatory, compliance with BS 5534:2014 is considered not only best practice, but also provides the best defence in the event of failures or disputes.
In the new build sector, the NHBC is especially vigilant in respect of the standard and, since July 2015, all new housing projects, regardless of size or phase; must comply with BS 5534:2014 to qualify for its 10 year Buildmark Warranty.
However, despite the new code now being two years old, many new roofs are being installed that do not conform to the standard either wilfully or through ignorance.
The changes are grouped into three main areas:
1. Mechanical fixing of ridge and hip tiles
2. Tile fixings
3. Underlays
Mechanical Fixing of ridge and hip tiles
The revised code of practice states that the use of mortar alone can no longer be relied on as a method of fixing as it
has been deemed to provide no reliable adhesion. Mortar can still be used but only if accompanied by mechanical fixings.
This means if mortar is used then additional materials are needed including a ridge/hip batten with fixings to rafters, and mechanical fixings for securing the ridge/hip tiles to the ridge/hip batten.
While the above secures the ridge/hip tiles it does not eliminate the risk of mortar failure, resulting in roof leakage and later repair work as the mortar can still crack and drop out of the mortar bed.
A simple way of avoiding all the hassle associated with mortar is to use the alternative of modern dry-fix ridge/hip solutions instead.
In the long term it is expected that this change will further drive the industry towards using dry-fix systems which meet the standard without the need for mortar.
Next week we’ll look at the issues around tile fixings and underlays; and how you can access technical advice to understand and conform to BS 5534 better.
For further information on Redland click here.
