Weather extremes and the future roof specification

Although experts are divided on the exact impact of climate change on our weather, the UK Climate Projections indicate we will face warmer and wetter winters and hotter, drier summers, as well as rising sea levels. Therefore we are likely to experience more extreme weather, such as heat waves and storms, over the next 25 years, leading to problems such as localised flooding and drought.

Last year, the Environment Agency Chairman Lord Smith warned that the extremes of weather seen in 2012 highlight the urgent need to plan for a changing climate. This doesn’t just mean looking at flood defences and water conservation measures, but how we construct our buildings to withstand extreme weather. Most buildings can cope with steady weather shifts but there is no real indication on how buildings are going to perform when exposed to increasingly hostile extremes of weather.

According to the Association of British Insurers, climate change could see annual losses from the three major storm types affecting the UK, increase by two thirds to £13.85 billion by 2080. Roofs are particularly vulnerable to storm damage, especially those using mortar bedded tiles. In fact, research from the country's largest mortgage and savings provider showed that 1.5 million homes are affected by storm damage each year, with the average roof needing 127 tiles replaced as a result.

Measures are already being taken by the roofing industry to help minimise the damage caused to roofs by storms and just like the weather, at Marley we take our roof tiles to the extremes when it comes to product testing. Rather than simply testing our products for ordinary levels of rainfall or wind, our roof tiles are subjected to wind tunnel testing for driving rain and deluge conditions equivalent to a once in 50 year extreme weather event, following the test methods stipulated in CEN/TR 15601: 2012.*

Whilst most roof manufacturers test their product to the same extreme weather conditions, they have different pass or fail levels. At Marley, we are particularly conservative and have set the level high, so it is much harder for our roof tile to pass. Local authorities should ask more questions about the testing processes that the tiles they specify have been through. We have already seen areas in the UK that should flood once in fifty years, having far more frequent occurrences of extreme weather, so it is best to err on the side of caution when it comes to product testing.

However well tested a roof tile is, if it isn’t fixed effectively then it won’t withstand storm conditions. The increasingly volatile weather conditions in the UK mean that ridge, hip and verge tiles bedded with mortar are more likely to become displaced due to strong winds, unless they are also mechanically fixed using screws, clips or nails. If local authorities want to future proof their roofs against weather extremes, then dry fix is certainly the best and most cost effective fixing method.

Dry fix provides full mechanical fixing of all roofing components to resist the highest wind speeds ever likely to occur in this country. Although dry fix has been around since the 1980s, demand for the products has surged in recent years as mortar has proved to be vulnerable in the UK's increasingly volatile weather conditions. This is because mortar can erode with time and tiles bedded with mortar are more likely to come loose when they are affected by strong winds. Mortar takes 24 hours to set so the higher the chance of frosting or rain, the less effective the mortar will be. However, with dry fix the tiles are fitted in place straight away with no setting time and are mechanically fixed regardless of the weather conditions.

In the private sector, the National House Building Council (NHBC) has advised that all ridges and hips on homes it guarantees must be mechanically fixed – either through a complete dry fix system or using mortar bedding with additional mechanical fixings. Local authorities could set a similar fixing standard for work on their properties or implement a dry fix only policy to ensure lower maintenance costs and guarantee against future storm damage.

At Marley, we have just launched a mechanical fixing kit for mortar bedded ridges and hips to help authorities who want to implement a more secure alternative to mortar alone, without going down a full dry fix route. However, unlike dry fix, provisions still need to be made to provide adequate means of ventilation at both high and low level.

It has been argued in the past that dry fix isn’t as cost effective as mortar, however if you take into account the long term maintenance costs associated with mortar then this is no longer the case. Plus as volatile weather increases, the fixing requirements are likely to become more stringent. We already have the zonal method which makes life easier for installers to determine which tiles need to be mechanically fixed and the Eurocode for wind loading on buildings. In addition, BS5534 (the code of practice for slating and tiling) will be updated in the next year and early indications are that this will result in more stringent assessments on a roof's performance with knock on effects to fixing specifications, products used and rafter lengths that they can be used on. 

All of this means that local authorities will need to depend on manufacturers more and more to provide suitable specifications to ensure that their roofs perform in the long term.

Taking a whole life view of roof cost and performance will also become even more important and those authorities who choose to implement a full dry fix policy will be well on the way to future proofing their properties. Roofs that local authorities are specifying now for new or refurbishment projects will be in place for the next 25 years, where weather extremes are set to become more frequent and action now in roofing specification will prevent long term repair and maintenance costs in the future.

Here at Marley Eternit, we are always on hand to offer practical and experienced support. Select an option below or call us on 01283 722588.