Simon Walker, Category Manager at SIG Zinc & Copper, discusses best practice for selecting metal cladding and roofing with Architecture Today’s Technical Editor John Ramshaw.

The popularity of metal cladding and roofing shows no sign of abating – and with good reason: it is aesthetically pleasing, recyclable, low maintenance, and long lasting. Today, there are countless products and systems on the market, each with its own benefits and draw backs, as well as individual specification and detailing requirements. Choosing metal cladding and/or roofing can therefore be a complex and onerous process. SIG Zinc & Copper has an extensive portfolio of zinc, copper, stainless steel, and aluminium products from leading manufacturers, including elZinc, VMZINC, KME Tecu, Mazzonetto, and Prefa. It is therefore ideally placed to provide best practice advice on material selection. Simon Walker, Category Manager at SIG Zinc & Copper discusses this important topic with Architecture Today’s Technical Editor John Ramshaw.

How should architects approach metal cladding and roofing selection?
Specifiers tend to approach design projects with a specific material in mind, particularly with regards to aesthetics. However, it is more beneficial to consider a broad range of performance and cost criteria at the outset, including buildability, life expectancy, patina over time, maintenance issues, and budget. This should help to define which type of metal best meets the brief and will be fit for purpose when the building is completed.

ElZinc Crystal Advance zinc shingles at Lady Bee Enterprise Centre, Shoreham Port, designed by ECE Architecture (ph: SIG)

How do different metals compare?
There are four metals commonly specified for cladding and roofing: zinc, copper, stainless steel, and aluminium. Zinc is highly malleable, enabling it to follow curved and angled planes, as well as deliver crisp edges that accentuate key features. It is particularly suited to marine environments and comes in a range of finishes and textures, including matt, pre-weathered, and natural, which patinates over time. There are also a wide range of standard and bespoke colours to choose from. Finally, zinc has excellent BREEAM credentials, can last up to 60 years, and is zero maintenance with no painting required.

Copper is also long lasting and excellent in marine locations but is considerably more expensive than zinc. Like zinc, it’s easy to form and therefore compatible with irregular structures and shapes. The material weathers naturally over time, although pre-weathered options are available and remain a popular choice. Last but not least, copper has a warm tonal range that is aesthetically appealing and desirable for a wide range of projects.

TECU Classic copper facade cladding from KME at Hive Student Residences in London, designed by Feilden Clegg Bradley Studios (ph: KME)

Stainless steel combines aesthetic appeal and durability with greater design freedom, as it can span longer distances in one run. A range of different surface treatments can be specified, although some finishes can ripple slightly. The material has a long-life expectancy of up to 80 years at a comparable cost to zinc. It is also highly corrosion-resistant and maintenance-free.

Aluminium is both lightweight and highly malleable. It is easy to work and can be laid on virtually any roof pitch exceeding three degrees – even in low temperatures. The material is available in a range of surface finishes and colours.

Designed by K4 Architects & Engineers, the VIDA Science Centre in Brno features Mazzonnetto’s Vestis aluminium standing seam cladding in a copper finish (ph: Mazzonnetto)

What facade and joint options are available?
There are five commonly used options: standing seam, flat lock or shingle, transversal joint, panel system, and engineered facade. Standing seam is one of the most cost-effective installation methods for metal roofs. Laid either vertically, horizontally or diagonally, metal ‘trays’ are connected by folding the raised edge to produce a projecting seam above the surface. The trays are anchored using hidden clips, which eschews the need for exposed mechanical fasteners.

Flat lock or shingle systems can comprise a wide range of machine manufactured geometric shapes, which are laid as overlapping tiles. Hidden fixings make them suitable for both flat and curved facades. Normally employed as part of a vented facade, the tiles are easy to install and can be cut, folded and edged at corner and boundary conditions.

Aluminium cladding in PREFA silver and anthracite matt on a private house in Freistadt (ph: PREFA/Wolfgang Croce)

Transversal joints are flat lock joints formed by making a 180-degree fold along each end of the trays to form a 5mm ‘jump’.

The panel system is suitable for flat or gently curved facades, with hidden fixings, and a transversal or longitudinal joint. Commonly used to clad soffits, it is aesthetically pleasing, cost effective and easy to install.

The engineered facade comprises large-format, individually demountable panels that are compatible with all wall constructions. They can provide a crisp, modern aesthetic in comparison with more traditional installations methods.

KME’s TECU Patina cladding at the The Cedars Suite Grove Hotel in Chandlers Cross, designed by Purcell (ph: Galliford Try)

What key issues should architects consider when specifying metal roofs and cladding?
The correct roof build-up is central to the success of the any building project. A tried and tested method is cold roof construction, which employs a ventilated cavity below the substrate, as well as a ventilated eaves and ridge to naturally dispel moisture on the underside. However, architects are increasingly using warm roof constructions with non-ventilated eaves and ridges as a means of obtaining thinner build-ups with finer details. If this type of roof is not properly built it can result in condensation problems. When used in warm roof construction, zinc must have the correct protective back coat for moisture control, as well as a breather membrane.

Confusion about the role and positioning of vapour control layers and breather membranes can also result in major problems. Fortunately, SIG Zinc & Copper can supply an NBS specification, bespoke details, and 3D build-ups of the roof installation for the contractor to help ensure metal roofing and cladding projects are properly designed and built.

ElZinc Rainbown Red standing seam zinc roofing and cladding on a private House in Bedfordshire, designed by Coles Architecture (ph: client, used with permission)

What are the benefits of using a specialist metal roofing and cladding supplier, such as SIG Zinc and Copper?
We are ‘product agnostic’, which means that we can recommend the right material and system for the application from a broad portfolio of products (SIG is the largest roofing supplier in Europe). We would never propose a solution where the product used was not completely fit-for-purpose. In addition to metal roof and façade panels, SIG can also supply specialist architectural fabrications, coils and strips in bespoke sizes, as well as guttering systems and ancillaries.

SIG’s metal cladding and roofing products are supported by a comprehensive design, technical support and supply service. SIG Zinc & Copper also has long standing relationships with established contractors trained by the Federation of Traditional Metal Roofing Contractors (FTMRC) and can advise on suitable contractors for your project.

Warranties are also critical when it comes to specifying roofing and cladding systems. Obviously, it’s no good if the warranty only covers the metal and roof fails due to a problem with the insulation or vapour control layer! Find out if your supplier can guarantee the whole build-up, materials and installation, as well as the length and credibility of the guarantee your client will receive.

Contact Details
For more information, please visit the SIG Zinc & Copper website.