An introduction to standing seam roofing design

Standing seam roofs are a popular choice with architects and specifiers looking for a design that really stands out. Simon Walker of SIG Zinc & Copper discusses what architects and specifiers should consider when designing standing seam roofing

Traditional standing seam has been in use for over a century, having been originally used on ecclesiastical buildings. Before long, strip standing seam was available panels were made up in short sheets and jointed, which was time consuming. Nowadays, modern profiling means you can cover up to 12 metres in a single strip. As a result, standing seam roofing is probably one of the most cost-effective ways of installing a zinc roof, and today can be seen on a wide range of building types.

Standing seam roofs are created using light gauge metals such as zinc, copper, aluminium or stainless steel. To achieve the desired aesthetic appearance seams follow the line of maximum pitch. The seams themselves are fairly fine, but in sunny weather the shadows they cast are clearly visible on the surface of the roof.

A unique characteristic of the malleable metals used in standing seam roofing is the subtle quilting that can appear naturally under different light conditions. This brings a bit of visual ‘vibration’ to the building which many architects appreciate but your client might be less keen. Quilting is more noticeable on steeply pitched roofs and facades.

Roof build-up
Standing seam roofing can be installed over a ventilated or non-ventilated roof construction allowing you to choose the best solution for the characteristics of your project. Trays are not self-supporting and require a fully or almost fully supporting substrate against which they rest and to which their clips are fixed.

Choosing which design is the most appropriate for a particular project depends on many factors and is best discussed on a project- by-project basis.

The standing seam joint
The longitudinal joint is a 25 mm high double lock standing seam. The double lock welt of the seam is raised above the water drainage part of the tray.

The standing seam is formed by profiling or folding strips and sheets into trays. An ‘undercloak’ is formed along one edge (this is the edge that is fixed with clips) and an ‘overcloak’ along the other. To make the joint, the overcloak is welted around the undercloak of the adjoining tray, covering the clips. The two trays are then seamed up using seaming irons or seaming machines.

Since the trays are only fixed along their seams, the distance between trays is determined according to expected wind loading, and tied in to commercially available coil widths.

Be aware that angle standing seam joints are limited to use on slopes pitched at least 25° or above.

Choosing the right cross joint
It is sometimes necessary to join standing seam trays end to end. This may be to introduce an expansion joint, as part of the flashing work around a chimney or skylight, or to produce a change in tray width on a conical roof.

There are different joint types available and the degree of roof pitch will determine which detail should be specified.

Each tray is anchored using hidden clips that are hooked into the seam and normally screwed or nailed to the substrate below. If the length of the tray is under 1.5 metres, fixed clips can be used throughout. Trays over 1.5 metres require a combination of fixed clips and sliding clips to allow for thermal movement of the trays, and provision for movement at eaves and ridge.

The distribution of the fixed clips depends on roof pitch – the steeper the pitch, the higher the band of fixed clips is positioned.

Avoiding pitfalls
When designing standing seam roofs architects should always consider the implications of the pitch and environmental conditions. For example careful consideration is needed when designing for particularly windy locations. The bay width of the trays will need to be narrowed otherwise an unwelcome fluttering noise can be generated by the movement of the pans of the trays or at worse, the standing seams can be lifted.

We would always recommend choosing a supplier or manufacturer with comprehensive technical support. The supplier should be able to provide technical information, including details, NBS Specifications, 3D build-up, and warranties.

It is also a good idea to look at the installation site with an experienced and accredited installer and take all these factors into account when determining joint type. A FTMRC registered and reputable hard metal roofing contractor should carry out the installation.

Want to learn more?
Why not attend a RIBA Approved CPD such as SIG Zinc & Copper’s ‘Specifying Hard Metals: Choosing the Right Product for the Project’ which aims to help specifiers demystify the confusion surrounding hard metal specification.

Simon Walker is category manager at SIG Zinc & Copper