Our technical webinar hosted with VMZINC explored how to correctly specify and install zinc facades and roofs.
Zinc roofing and cladding has long been favoured for its aesthetic appeal, durability and sustainability. But how can architects ensure they are following best practice when it comes to specifying and installing different zinc systems? What design aspects should they pay particular attention to? And how should they approach issues relating to procurement and budget? These questions and more were explored in this Architecture Today webinar, in partnership with VMZINC.
In association with
Baron Haussmann chose zinc to transform Paris in the 19th century
History
From a historical perspective, zinc is perhaps most closely associated with Baron Haussmann’s urban renewal programme in Paris (1853-70). Much of this architecture required roofs with a slope of three degrees, which is still the minimum angle for zinc roofs (as built). The material was also widely used in the UK during this period, although mainly for civic buildings.
A good example is the Picton Reading Room dome in Liverpool (1879), which was refurbished after more than 130 years of service. While most of the original design was kept, current regulations meant that panel widths had to be reduced and standing seams were incorporated between the batten caps. Current corrosion rates are less than two microns per year – a sheet of zinc is at least 700microns thick.
Substrates
Correctly designed substrates are key to successful zinc roofing projects. A cold vented roof must have an air inlet at the base and ridge (minimum 10mm open), and a minimum 50mm deep continuous cavity between the back of the substrate and the insulation. When a vented plywood support deck is used, VMZINC PLUS with a 60-micron underside coating should be specified to protect the backside of the zinc from acidic glues that may be present in the timber.
Cold roof build up – vented plywood
A non-vented warm zinc roof must have a fully supported, unbroken, self-sealing Aludex Max vapour barrier, with a continuous layer of rigid insulation above (reducing thermal bridges), followed by a VMZINC breather membrane, and then a VMZINC PLUS covering.
The Structural roof has a BBA certificate and can be used with both PIR and mineral board insulation. Bearing plates and pegs greatly reduce thermal bridges thus further enhancing the system. The fully supported Aludex Max vapour barrier which increases air tightness can be seen below the insulation and the VMZINC breather membrane above.
Low profile G3 ridge
Standing seam roofs
VMZINC standing seam systems are highly flexible and can cover almost all roof forms. Both warm and cold roofs have no fire penetration or flame spread following BROOF(t4) tests. Specifiers should remember that the right flashing must be used for the right detail, and eave details need to be accommodate thermal movement while remaining weathertight.
Zinc aesthetics
Zinc can be chemically treated to give a range of different aesthetics, but always with a hint of grey. Natural zinc is shiny but forms a patina when it reacts initially with water and then with carbon dioxide. After 3-10 years an even middle grey patina is formed, but it takes time for this to become uniform.
ANTHRA-ZINC roof at the Bourne Estate in London
Pre-weathered QUARTZ-ZINC imitates naturally weathered zinc through a phosphatation process and changes very little over the lifetime of the roof or facade. Pre-weathered ANTHRA-ZINC’s dark grey appearance has proved popular for both wall cladding and roofing.
PIGMENTO Brown roofing and cladding on a private house in Berkshire
VMZINC’s `off the shelf` PIGMENTO range comprises Blue, Red, Green, Brown, Grey, Storm Grey, and Charcoal Blue colours. The surface tone is created by adding mineral pigments to a durable pre-weathering zinc, which is then sealed with a protective coating. Azengar, which is an engraved zinc, combines both mechanical and chemical treatments. It can be used for roofing and cladding. All finishes can be used for all systems, including standing seam.
Standing seam cladding
Stand seam facades
Warm wall construction is possible, but most clients and organisations such as NHBC prefer vented cold wall construction. It should be noted that zinc is non-combustible following EN13501-1. Natural Zinc, Azengar, QUARTZ-ZINC and ANTHRA-ZINC are all therefore A1. Coated products, such as PIGMENTO and VMZ PLUS, are A2 classified, but still permit the zinc to be used on all buildings over 18 metres high. For projects where EN 13501 A1/A2 materials are required, a 0.7mm thick galvanised steel support deck can be used in place of a timber one.
Standing seam panels will never be completely flat but using 0.8mm thick zinc and 430mm wide single lock panels will help with this. For ease of installation, it is recommended that panels measure no more than four metres in length.
ANTHRA-ZINC and QUARTZ-ZINC were used to renovate Parsons Tower in Newcastle
Zinc flexibility
Almost immediately after zinc was first used on roofs in the 19th century, it began to be employed as a material for roof ornaments – and still is. It is also highly malleable, as evidenced by the zinc dormer windows and balustrades that form part of the Poundbury development in Dorset. Zinc’s lightweight and flexible properties mean that it is ideally suited to renovation and retrofit projects.
Flat lock cladding at Kingsland wharf, London, designed by JCMT Architects
Facade options and gutters
The choice of systems for zinc roofs is fairly straightforward, but for facades the options are far greater and include flat lock panels, bespoke shingles, and diamond shingles. The latter can be used for roofing on slopes above 30 degrees. Flat lock panels come in many shapes and sizes, but should not be specified larger than 3000x600mm.
Hidden box gutters should have falls of 1:100
Hidden box gutters are common features on zinc roofs and should have falls of 1:100, overflows and expansion joints. Hanging gutters can also be used and should be fitted with a minimum fall of 1:200. A range of half round gutters in QUARTZ-ZINC and ANTHRA-ZINC with hidden brackets are stocked in the UK. Rectangular and OGEE gutters are also available.
Mozaik cladding
Rainscreen facades
The Mozaik panel system is a good option for zinc facade panels measuring up to 600mm wide. Panel depth can be altered to 40, 60, 80 and 100mm, giving the possibility of a more textured facade. The reveal joints are always 15mm wide.
Sine wave cladding panels
Horizontal ship lap panels with a 200mm coverage width can be installed on metal or timber cladding rails. The panels themselves can have a depth of either 13mm or 20mm.
Sine wave or corrugated panels are available in all finishes and fasteners and can be installed both horizontally and vertically. The standard wave size is 18x76mm. The panels can be perforated and/or curved.
Interlocking panel cladding
Interlocking panels are probably the mostly commonly used zinc rainscreen system. They have a depth of 25mm, and the most common centre-to-centre distance is 300mm, including a 10mm or 20mm reveal joint. Interlocking panels can be installed horizontally or vertically, are tested to the CWCT protocol, and will always sit flatter than a standing seam facade.
Budget and procurement
The cost of a zinc roof or wall will depend on the system used, as well as the size and location of the project. Most zinc systems can be supplied and fitted for £100-£200/m². Most products are stocked by UK or Ireland-based distributors making zinc rapidly available.
It is critical that standing seam roofing and cladding is installed by a competent ‘hard metal contractor’. VMZINC@WORK partners have a track record of successfully installing zinc roofs and walls, they also know and understand our recommendations following training. Health and safety regulations must be followed, with all risks assessed, PPE used, correct lifting and handling employed, and working at height applications carefully accessed.
