Roofing material matters and the specification issues can be confusing, so Ged Ferris, Marketing Manager at slates and cladding specialist, Cembrit, is on hand to offer guidance.
As many architects are aware, roofing slate is available in both natural and man-made varieties. In order to make the most suitable choice for a particular project, it is necessary to have a good understanding of the unique qualities of both, as well as the kinds of application for which each is best suited.
The natural choice?
Natural slate is a traditional building material, with a heritage that goes back to Roman times. It offers a fantastic combination of aesthetic appeal and exceptional durability. Natural slate can become a major contributory factor in a building’s whole life costs, which is important since environmental issues are moving to the forefront in all areas of construction. A well laid slate roof will enhance any building and give problem free protection for the lifetime of the building. However, natural slate also satisfies on that other buzzword so common throughout product specification – sustainability! As well as lasting the lifetime of the building, natural slate can be salvaged and re-used. In fact, reclaiming natural slate for roofing and cladding has been common practice since the middle of the last century, with worked stone recognised as a valuable building material for many hundreds of years, as it is today. Natural slate, tested to BS EN 12326 Part I and meeting the highest relevant ratings will be unaffected by normal extremes of temperature, and highly resistant to acids, alkalis and other chemicals. This means that it is resistant to acid rain and atmospheres that contain sulphur dioxide, whereas man-made products commonly discolour due to weathering or the growth of lichens (although surface coatings can delay this process).
Natural slate often respects the traditional or local character where it is used and, as a natural product, features variations in colours, sizes and textures. This is especially important in conservation areas, where slate selection must match existing roofing materials on surrounding buildings. Historically, slates were from a local source which means that usually there is a ‘type’ of roofing material particular to a location. However, nowadays with more quarries available worldwide, suitable alternatives can be found to match most British origin slates found on roofs throughout the country.
Fibre cement slate
The advances in the production of fibre cement slate now mean that a wider range of projects can benefit from a slate roof. Fibre cement slates come in a uniform size, thickness, and shape eliminating the time needed to sort on site, as well as offering added versatility when architects want to use complex roof designs on buildings.
Fibre cement slates are pre-drilled for quick and easy fixing saving time on site, and therefore also lowering costs. In addition, the slates can be cut and mitred using simple hand tools. This adds to the ease of installation and can also reduce waste on site through breakage. This consistency means it is easier for these products to be used on intricate roofs in that they are suited for use by the less experienced roofer.
Budget considerations may lead some to fibre cement slates, since they are cheaper than natural slate. Although natural slate may be favoured in conservation areas the visual quality of fibre cement slates means that nowadays they can blend seamlessly with historic surroundings when natural slate cannot be sourced or is too expensive. In less sensitive areas fibre cement slates can offer the architect versatility on complex designs as well as a huge variation in colours available. High quality products have an appearance close to that of natural slate. For example, Cembrit’s Moorland slate has an attractive dressed edge making it an ideal solution where presentation is important.
Which slate for the job?
Natural slate is great to look at, and is extremely tough. That said, it does need to be sorted and worked with, which adds time on site. Fibre cement options provide a cost-effective and conveniently sized alternative, and the improved quality of modern fibre cement slates has improved their durability and strength, some coming with a 30 year guarantee. Modern slates are also resistant to fire, chemicals and fungal growth, and are unaffected by temperature changes as well as being vermin and rot proof. Meanwhile, the low fixed weight of fibre cement slates allows economical use of timber roof trusses. However, sometimes only natural slate will do, for example, when it comes to matching the roofing of a particular area or group of buildings.
In a nutshell, fibre cement slates offer consistency and convenience, whereas natural slate provides authenticity and character. As a supplier of both natural and fibre cement slate, we are in a great position to give unbiased recommendations as to which product suits your project.
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