As the NHBC makes mechanical fixing mandatory for all mortar bedded ridges and hips, John Dodd, technical manager at Marley Eternit discusses the significance of this announcement and asks whether it actually goes far enough to address the issues of mortar bedding tile and slate roof components.
A recent revision to the NHBC Technical Standards, means that supplementary mechanical fixing has now become mandatory for all mortar bedded ridges and hips, which marks a positive step in our industry, as it further strengthens the case for dry fix systems.
It should come as no surprise that the NHBC have taken such measures, with data released by them in 2010 showing that more than half of valid pitched roof insurance claims were related to mortar issues, with defects reported as soon as three years after completion.
The roof of today has to meet a range of challenging and often conflicting requirements; it needs to be weather-proof and aesthetically pleasing, provide adequate ventilation whilst being quick and easy to install, all with minimal requirement for maintenance and maximum durability.
It is the diversity of these demands upon the roof as a platform, combined with increasingly volatile weather conditions that expose the vulnerability of mortar across all parts of the UK, and surely must have contributed to the decision by the NHBC to introduce more stringent regulations when it comes to the continued use of mortar.
Indeed, mortar needs to be applied by skilled operatives, using the correct materials and mix ratios. It is vulnerable to erosion over time, and ridge, hip and verge tiles bedded with mortar are more likely to come loose due to strong winds unless they are also mechanically fixed using screws, clips or nails. Mortar also takes 24 hours to set so the higher the chance of frosting or rain, the less effective mortar will be. Differential movement of the roof structure can also cause the mortar bedding to crack, thereby destroying any chance of tensile adhesion to complementary components.
However with dry fix, the tiles and components are secured in place straight away with no setting time and are mechanically fixed regardless of weather conditions or movement in the roof structure.
Plus, whilst there are myths that dry fix systems are much more expensive than mortar, mandating the use of mechanical fixings for all bedded ridges and hips will surely put an end to these previously inaccurate estimates.
Contractors are constantly looking for products that are time and cost-efficient. Dry fix systems deliver both of these requirements, and with the new NHBC requirement making the technical and economic benefits over mortar even clearer to see, it is something which should indeed be welcomed throughout our industry.
However with such overwhelming evidence in favour of dry fix systems, should we in fact be considering taking even stronger measures and banning the use of mortar for all new build properties?