Dry Fixing

Can Redland accessories be used with double lap slates?

Most Redland dry fix products for use with either flat interlocking tiles or plain tiles may be used with double lap slates with minor changes to the installation instructions. RedVent EavesVent: fix as normal. Dry Hip: follow instructions to ensure hip batten is at correct height and the cut slates adequately fixed. Rapid and Rapid Vented Ridge: the use of Rapid Vented Ridge with natural slates depends on the secure fixing of the top course of slates since there is no restraining force created by the ridge tile. Contact Technical Solutions for advice. DryVent Ridge and Monoridge: follow instructions to ensure correct relationship of the top battens and underlay relative to the ridge. Abutment Vent: follow instructions to ensure correct relationship of the top battens and underlay relative to the abutment. Valleys: a specific version of our 125 GRP Valley is available for use with natural slate. GRP Secret Gutter: should only be used with a cover flashing.
Cambrian Mitred Hip and Ambi-Dry Verge are not suitable for double lap slates.

 

Why is it preferable to dry fix the perimeters of a roof?

The perimeter areas of a roof such as the ridge, verge and hip are the most vulnerable to damage by wind uplift. The traditional method of fixing tiles and fittings at these points involves wet mortar bedding or wet fixing. However, the strength and consequently life of mortar is highly dependent on the skills and knowledge of the roofing contractor. Incorrect mixes, poor preparation and careless workmanship can all lead to problems and eventually to costly repairs if the roof is to remain weathertight in the long term. During the storms of the late 1980s and more recently most of the damage to roofs was as a result of failing mortar. Indeed two-thirds of all current roofing claims against the NHBC Buildmark Warranty for new houses involve the failure of mortar.  The latest revision of BS 5534, Slating and tiling for pitched roofs and vertical cladding – Code of practice, now requires that all ridge, hip and verge tiles on a roof are mechanically fixed whether mortar-bedded or not as the code of practice states that mortar alone cannot be relied upon as a fixing method. Although mortar can still be used it must be supplemented by mechanical fixings. While the mechanical fixings secure the tiles, however, mortar can still crack and drop out causing the roof to leak requiring repointing and ongoing maintenance. Alternatively developments in roofing technology have led to the introduction of 'dry fixing' systems. As the name suggests dry fixing does not use mortar but secures the hip, ridge or verge tiles to the structural timber using screws or clips as part of a weathertight system. Dry fix products are also much simpler and quicker to install and their success and long-term durability is not dependent on the skill of the roofing contractor. They can also be fixed in wet weather, which can have a significant effect on the build schedule. The advantages of dry fix technology coupled with recent changes to fixing standards make dry fixing increasingly preferable to mortar bedding for fixing the perimeters of a roof.