The added benefits of dry fixing
Though dry fixing has become an accepted part of roofing practice, it has never replaced traditional mortar fixing to the extent that many forecast when the concept was introduced. A succession of relatively mild winters has in some respects masked the potential for frost-associated mortar problems, prompting many house builders to maintain that dry fixing has, until now, been an unnecessary additional cost. However, the past two years have seen consistently severe weather conditions throughout the country and as a result claims to the NHBC under its 10-year warranty scheme have risen steeply.
The highest proportion of these claims have been roofing related with the most common being linked to mortar and condensation issues. This had already prompted the NHBC to issue a directive requiring vapour permeable underlays in cold roofs to be supported by high level ventilation. In November, this was followed by another which required dry fixing of ridges, hips and eaves for all home starts after 1st January. The decision was based on sound statistical information as it had become clear that dry fix was already in more widespread use in areas which face the most severe weather conditions. In some regions, the level had reached over 80% of new builds and where this was the case there were correspondingly fewer claims resulting from storm damage. Despite long periods of sub-zero weather in 2010 and 2011 the trend remained constant. For homes built outside the NHBC warranty, there is also a higher incidence of dry fixing. Housing associations in particular see it as a means of avoiding the risk of unforeseen and premature refurbishment costs while providing scope for more accurate long-term maintenance forecasts.
Klober was among the first dry fix product manufacturers and has consistently drawn attention to the potential pitfalls of mortar fixing. However, Technical Manager Graham Copson added, “Some early dry fix products were not designed with the installer in mind so though they provided a more consistent standard of workmanship they were not always popular. Other criticisms levelled against them were that joints were unsightly and that they were difficult to align. Mortar is always needed on site so many builders allowed the supposed drawbacks to outweigh the benefits of being able to undertake work in wet conditions and eradicating incidences of snagging. Klober manufactures products for universal use and so have to ensure they are easy to install. We welcome comparison against other dry fix and ventilation materials.”
It is a touch ironic that the two NHBC guidelines mentioned should have combined to work in favour of dry fixing. Products such as Klober’s Roll-Fix and Uni-Dry Ventilating Ridge have provided universal ventilating dry ridge and hip options for some years. Both are suitable for use with the majority of concrete interlocking tiles and plain tiles as well as natural and fibre-cement slates. Their value has grown as standards of loft insulation in cold roofs and the consequent risk of condensation have increased. This has increased further as ridge and hip tiles bedded on mortar should now be ‘mechanically fixed with self sealing non-ferrous fixings into timber battens’.
In addition to dry fixing of ridges and hips, use of the Klober Uni-Dry Verge is just as straightforward as it is suitable for most concrete interlocking tiles with a 280mm – 345mm batten gauge. Verges are highly susceptible to wind uplift and even before mortar replacement becomes necessary, the initial signs of failure are often unsightly. Few now argue that dry verge performance is matched by better overall appearance, to such an extent that many house builders insist on dry fixed verges while continuing to mortar-fix ridges and hips. No specific skills or tools are required and all that needs to be remembered is that the ridge batten must overhang the gable wall by 35mm to allow the Ridge End Cap to be fixed. No overhang is required if using a block end ridge.
Dry fixing is unaffected by settlement or movement and its use on pitches from 12.5° – 90° makes it suitable for most housing styles and designs. For the contractor, such ‘universal’ products can be used regardless of which manufacturer’s roof covering is supplied while the real value of dry fixing at the ridge has increased still further as a result of the two NHBC directives. The problem of unsightly mortar runs in mid-winter will at last be a thing of the past.
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