Choosing metal for roofing and cladding has become a popular option for many homeowners. Not only because of its aesthetic appeal but also for its long lifespan, low-maintenance requirements and, as a 100% recyclable material, it also contributes to high BREEAM ratings.
As metal roofing has grown in popularity, so too has the choice, and this has resulted in a certain level of confusion on product quality, detailing options and conflicting advice on construction methods.
Here, we look at what you should consider when choosing a metal roof.
Know your metals!
The most commonly-used metals are zinc, copper, stainless steel and aluminium. Each metal has its own pros and cons. Rather than starting off with a specific material in mind to achieve a particular visual effect, it is best to select a metal that meets the requirements of your project.
• Zinc is a malleable metal that can easily follow curves and angles in the design and produce crisp lines that accentuate features. Available in a range of finishes and textures, including natural, which will patinate over time, pre-weathered, matte and textured effects. Also available are a wide range of standard and bespoke colours.
• Copper has a warm colouring which lends a certain elegance to the building. Easy to form, the metal will adapt to many architectural styles including irregular structures and shapes. Copper naturally weathers over time although pre-weathered options are available for an instant effect.
• Aluminium is one of the lightest metals available and can be mounted on virtually any roof pitch exceeding 3º. Incredibly malleable and easy to work with, it can even be installed at low temperatures. Available in a range of surface finishes and colours.
• Stainless steel not only offers a truly dramatic visual impact but due to its physical properties provides greater design freedom. The metal can be used in thinner pieces, resulting in a lower weight, and for very long parts in a single section. Various surface treatments and colours are available.
Facade and joint options
The look of a roof or cladding depends on how it is laid and the type of joint used.
A cost-effective installation method, ‘trays’ are joined together by folding the raised edge to produce a projecting standing seam above the surface. There are no exposed mechanical fasteners on view, and the trays are anchored using hidden clips. The seams themselves are fairly fine, but in sunny weather, the shadows they cast are clearly visible on the surface.
Distance between trays is determined according to expected wind loading and available coil widths. Be aware that angle standing seam joints are limited to use on slopes pitched at least 25° or above. They can be installed in a vertical, diagonal or horizontal direction.
Shingles are machine-manufactured geometric shapes laid as overlapping tiles. Popular on projects for their ease of installation, they can be cut, folded and edged as required at the boundaries. With a wide range of shapes available, they provide a unique look to your project.
Hidden fixing makes this a suitable option for flat and curved facades. Shingles are normally used with a vented facade construction.
The panel system is a popular technique due to its reasonable cost, attractive appearance and ease of installation. It can be installed in a vertical or horizontal direction and is commonly used to clad soffits. Fixing is hidden and usually direct.
One of the major factors in the cost of your metal roof will be the location of the project and availability of experienced installers. However, it is worth remembering that a well-installed metal roof will require virtually no maintenance throughout its lifetime, which can be 30 years or more.
Installing a metal roof is a skilled job. We advise using either a manufacturer- or supplier-approved contractor who has received training and monitoring in the installation of their products. They should also be a member of the Federation of Traditional Metal Roofing Contractors (FTMRC).
Elements that you should be aware of
One of the biggest issues with zinc roofing is underside corrosion, which can occur if the wrong substrate or build-up has been fitted, in particular the vapour control layer.
The most common build-up is a cold roof design which provides a ventilated cavity below the substrate and ventilated eaves and ridge. This allows moisture on the underside to be naturally vented out. Increasingly, warm roof constructions are being specified on metal projects as a thinner build-up option. The warm roof has no vented space and can lead to condensation if not constructed properly.
Picking your supplier
Choose your supplier carefully. They should provide a comprehensive design and supply service and offer advice on the most suitable product, build-up and installation method for your project. Technical guidance should include bespoke detailing, NBS specification, calculations and 3D build-ups. Suppliers should consider the implications of the pitch and environmental conditions of your project. For example, a windy site may require narrowing the tray width on a standing seam roof to minimise movement of the trays.
Finally, does your supplier offer a warranty and, if so, what does it cover? If it only covers the metal and your roof fails due to the insulation failing, you could end up with an expensive repair bill. When doing your research, you need to make sure the guarantee covers the entire build-up, including materials and workmanship.
With so much choice on the market and with an endless list of decisions to be made, choosing the right metal for your project can certainly be a challenge, but independent specialists from SIG Zinc & Copper are on hand to help you make the correct choice for your project and your budget. Over the years, we’ve worked with a wide range of different manufacturers and products, so we can help you make an informed choice. What’s more, we also offer design advice for your project at no additional cost to you.
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