For today’s architectural strategies, you would be hard pressed to find a building material with better credentials than natural slate. With timeless aesthetic appeal and inherent durability, it has long been favoured for roofing applications. Here, Steve Pearson, UK Director from CUPA PIZARRAS highlights why natural slate remains popular and explains how it is evolving to meet even more project requirements.
When it comes to finding a building material that can establish an architectural design intent and see it through to a working reality that will stand the test of time; natural slate is so often the solution. From an aesthetic perspective alone, it can benefit new-build properties looking to incorporate a warmth and texture to the exterior of the property that will fit seamlessly into natural surroundings as well as complement more contemporary finishes. Renovations where roofing needs to closely replicate original materials will also benefit from the specification of natural slate.
Natural slate is a metamorphic rock, formed from sediment and mud laid down over 450 million years ago that has since undergone tectonic compression. There are a variety of different types of natural slate available, each with its own origin and geology which results in a specific colour and texture combination. The appearance of natural slate can vary even between closely located quarries – from smooth blue black to rougher, dark greys – allowing a wide variety of different design aspirations to be met. However, for high-quality natural slate, architects should turn to Spanish producers as Spain is home to the largest reserves of tectonic natural slate in the world.
Natural slate has been used for traditional pitched roofing for many hundreds of years. Thanks to its flexibility as a material, a wide variety of roof shapes can be achieved using natural slate, from m-shaped to gambrel, Dutch to butterfly and easily incorporating hips, valleys, gables, dormers. By adding characteristics like a steep pitch and extended floating gables, a natural slate roof can be taken from functional necessity to a striking and eye-catching design feature.
These options are made possible thanks to the natural slate’s workability – it can easily cut onsite to help complete intricate details – and by the wide variety of sizes and shapes. Although, the most common slate format in the UK remains the standard rectangle; but many manufacturers also offer shapes including bull-nose and half-moon, meaning that for something truly unique, small decorative and ornamental elements can be incorporated into a roof or façade, an approach popular in Germany and other European countries.
Even with traditional rectangular shaped slates, the choice of sizes used across a roof does not have to be uniform: some opt for larger slates, as seen in London, or smaller slates as is popular in Scotland. In fact, for many centuries, the use of random sized slates laid in diminishing courses – originally born out of the need to utilise any and all Scottish slate quarried – creates a distinctive characterful finish.
Beyond the traditional pitched roof, we are seeing a trend for bringing the visual appeal of natural slate to interior design schemes as well. The concept of a space that connects the indoors and outdoors is by no means new; but since its shift into widespread popularity natural slate is being increasingly adopted for feature walls. Natural slate can even help to complement and enhance a biophilic design approach.
Furthermore, natural slate provides a sleek and striking cladding material, illustrating its place even on flat roofed buildings. Naturally hardwearing and with a low water absorption rate, natural slate can create a double-wall construction rainscreen cladding, ensuring continuous ventilation and aiding internal temperature control. A lightweight alternative to brick, natural slate cladding is also ideal for structures where material weight is a concern – for example if a building or part of a building is leaning. Furthermore, natural slate’s A1 rated non-combustibility is another important selling point. In partnership with a metal bracket installation method, crucial given the recent changes to building regulations.
Whether it is being specified for the external envelope or as a design feature within an interior scheme – natural slate ensures that aesthetic and performance requirements are met while also ensuring a low environmental impact. A 100% natural material, once quarried or mined, it needs little processing before it can be used on a roof, far less than comparative roofing materials. A study conducted by the University of Bath as part of its Inventory of Carbon and Energy (ICE) project illustrated that the production of slate produces much less air pollution and uses less water than other roofing materials including clay, concrete and limestone tiles, copper and lead. The embodied carbon per square metre of roof area (KgCO2/m2) was also calculated for each material: for slate it was found to be just 0.15-1.62 KgCO2/m2 compared with 10 and 27 KgCO2/m2 for concrete and clay respectively. Copper was calculated to have 20-28 KgCO2/m2 and lead 41 KgCO2/m2.
However, beyond the material itself, trusted manufacturers will always encourage architects to reach out and talk to their teams about their production processes and what they are doing to support sustainable building strategies. This requires a holistic approach from the manufacturer and architects should question what is happening to reduce carbon emissions, the restoration of quarries, water reuse and recycling as well as the traceability and quality assurance of their materials.
At CUPA PIZARRAS, we are proud to be Carbon Neutral through reducing our emissions and offsetting all the carbon used in our operations and surpassing all international standards in terms of the quality of our slate. Several of our products are also BRE certified, proving the quality and transparency of their lifecycle, and listed in the Green Book database.
Finally, we feel passionate that natural slate offers unrivalled credentials on all fronts. With a timeless visual appeal, slate goes beyond trends with its ability to bring character to classic or contemporary schemes. The elegant appearance of high-quality Spanish slate remains intact during its entire lifespan; as it will not lose its colour or sheen, which other materials can fall victim to. These unmatched technical properties will also ensure that architectural intent and vision are a success for the long-term – creating beautiful buildings that will stand the test of time.