Zinc has been widely used in Europe for centuries but remains largely overlooked in the UK. Alex Murphy of VM Zinc looks at its key benefits and describes how to make zinc installations a success.
Robust, easy to maintain and long lasting – the benefits of zinc as a roofing material are no secret to Paris’ couvreurs (roofers) who have used it to keep the French capital’s buildings dry for the last 200 years. Yet while zinc’s benefits are well known on the continent, its application here has remained relatively limited. But why?
Its reputation in the UK as a purely contemporary material could not be further from the truth. While specially fabricated interlocking cassettes are often used to adorn the facades of modern buildings, traditional standing seam zinc roofs have protected the likes of Liverpool Central Library since the 19th century.
If you needed a reason to trust the durability of zinc, Liverpool Central Library is a case study worth looking into. First installed in 1879, the original zinc roof did not need to be replaced until 2011, and while it is not uncommon for a zinc roof to last more than 80 years, a lot of its longevity on projects depends on how well the substrate has been designed.
Trapped moisture between the build-up and the zinc is often the leading cause of failure in a zinc roof. Without allowing the moisture to escape, white rust can begin to form on the underside of the panels. The best way to avoid any potential problems is to stick to an accredited build up and a product that won’t let you down.
For example, backside coated zinc allows the material to be installed on ventilated plywood as well as warm (non-ventilated) substrates. The product consists of zinc (in all finishes) with a 60 μm coating applied to the underside, thus allowing a wide variety of substrates to be used and eliminating the risk of the formation of white rust.
As well as this, BBA Certificates are available for some non-ventilated warm roof systems. BBA certified systems give a wide range of benefits. For over 40 years, Agrement certificates have been supplied by the BBA in order to give unbiased information on the performance of a system. By selecting a BBA system an architect is likely to avoid problems at a number of stages in the building process and queries about the performance of key products.
Knowing how to construct a roof is important for an architect, but so are the potential restrictions of the material that is being specified. Parts of the UK can be subject to extreme weather conditions, and while zinc cladding and roofs have been applied to buildings up and down the country, wind uplift is an important consideration, particularly given the tightened requirements in BS5534:2014.
A zinc clad wall even survived the 175 mph hurricane winds of Katrina in New Orleans in 2005 when many buildings were destroyed; proof that a properly installed zinc roof or facade can withstand even the most extreme wind uplift.
Correct installation is therefore essential for ensuring the durability of a zinc roof or facade. Stainless steel sliding clips have a moving component to allow free movement of the panel when it is under expansion and contraction. Each clip must resist a pull-out force of 50 daN. Standard panel width is 600 mm, however for aesthetic or wind up lift reasons 530mm or even 430 mm wide panels can be used.
But what about maintaining the natural aesthetics of zinc? All zinc will develop a patina over time, and though this is truer of natural zinc than of the pre-weathered options available, all zinc types will change slightly throughout their life.
Cleaning is generally not recommended for zinc roofs and walls, as rain water performs this task very well. Non-rinsed surfaces such as soffits and some facades, especially in coastal areas, may exhibit some minor cosmetic staining, but specifiers can rest assured this is purely cosmetic.
Acidic woods such as oak, red cedar and chestnut should be avoided, as well as non-galvanised steels and copper, which can react with and damage the zinc. Contractors and architects alike should look to avoid contact between zinc and these materials, as well as certain others.
While standing seam systems are always a popular choice for architects due to their classic look and relatively easy installation, there are a number of other rain screen systems available which offer alternative aesthetic options. Flatlock and overlapping panels, interlocking cassettes and sinewave panels all offer
something visually different for the architect to consider, yet still maintain the durability and long life zinc is renowned for.
Simultaneously classic and contemporary, and robust in nature, possible uses are endless and zinc applications are limited only by architects’ imaginations. If an appropriate substrate is used and the zinc is installed correctly, there is no reason why a zinc roof should not provide beautiful, natural, long lasting protection to a roof or facade for years to come.
Alex Murphy is a technical sales assistant at VM Zinc