Sheeted roofing offers a modern look, but correct specification is vital to ensure longevity.

Over the last decade, metal sheeting for roofs has gained significant ground as a preferred roof covering option for modern buildings, whether for residential, commercial or industrial buildings. WALLS & ROOFS spoke to industry players to find out why and get their advice on specifying sheeted roofs correctly.

“From an architectural point of view the main considerations when choosing a roof covering are aesthetics and longevity, and Rheinzink roof sheeting offers just that,” comments Stephen Wilkinson, business manager at Rheinzink South Africa.

“Metal is a highly versatile material to form and drape, and can accommodate complex design demands which tiles or cementitious built-up roofs cannot,” says Sally Stromnes, Strategic Marketing Planner for the Safintra Roofing Group. “Not only is metal roofing light yet very strong, but it also provides a truly watertight covering when correctly installed, with the appropriate flashings, closures and lap sealant. It is also more cost-effective than other roof coverings over the service life of the roof, which includes the costs of maintenance,” Stromnes states.

Design versatility plus sustainability

Wayne Miller, general manager of BlueScope in Southern Africa, adds that besides offering the architect an outstanding design option, a steel roof is a sustainable solution. “Steel roof coverings are chosen for their appearance, flexibility in design, versatility and strength against the elements, such as withstanding a hail storm,” he says, “but in addition, with today’s advanced technology, certain high SRI pre-painted steel roofs can facilitate a much cooler building than before.”

Global Roofing Solutions’ National Projects and Specifications Manager, Lyle Jeffrey, remarks that thermal efficiency is increasingly associated with steel roofing nowadays with suppliers using thermal technologies in their painting systems. “The big drive behind this is sustainability and with steel being recyclable, it has one of the lowest carbon footprints when it comes to a roof covering,” he says.

“Sustainability is increasingly important for green credentials of projects,” highlights Stromnes. “And with modern clamps and grips, metal roofing provides the most efficient base onto which to mount solar panels and roof-top fixtures without voiding the roof material warranty.”

Correct roof sheet specification
According to Jeffrey, before choosing a roof covering, it is necessary to understand the project – the purpose of the facility, its location and the accompanying environmental factors.

“Once these have been ascertained, then by process of elimination one can select a suitable material and determine whether to opt for a standard product or the premium version,” he says. “In this regard, the location is highly critical in specifying the appropriate option since it will have a significant impact on the longevity of the roof. For example, a normal coated metal roof sheet isn’t suitable for projects within a specified distance from the high-water mark. As a rule of thumb, aluminium is recommended for buildings within 400 meters of breaking surf, thereafter the premium coated products ought to be utilized up to 5 km inland.  

Uncontrollable environmental factors

Miller explains that the marine influence is especially severe within 200m from breaking surf, while a moderate influence is pertinent up to 1 000m, after which it is considered benign.

He points out that this is one of the uncontrollable environmental factors impacting the performance of steel roofing, which can be minimised by choosing a material appropriate to the conditions under which the steel sheet must perform. Others factors that may impact on the corrosive nature of a particular site include prevailing winds, rainfall, time of wetness, temperature, shelter and areas not naturally washed by rainfall.

Industrial activity and harsh environments

“In addition, the concentration and nature of industrial activity and the effects of the combustions of fossil fuels must be taken into account in some localities, whilst the direction, intensity and nature of prevailing winds can also exert an influence,” Miller states.

For industrial roofing applications, as well as farming sheds and buildings with indoor swimming pools, the internal and/or external environment of the building must be considered, according to Miller. “There are many activities carried out in sheds and industrial buildings that are quite severe in their effects on steel products. Where the roof cladding is subject to heavy dust, emissions, containment fallout or contact with corrosive chemicals, it is essential to consult the roofing supplier for advice on the correct product to use,” he advises.

Ten steps to specify metal sheeting for roofing

According to Stromnes, there are very clear steps in the design and decision-making process which will ensure that an appropriate roof covering specification is arrived at:
Ten steps to
Courtesy of Safintra

What can go wrong?
Stromnes emphasises the importance of selecting a roof appropriate to the weather and wind conditions of the location and a material that will last the expected service life. “Don’t skimp on the material to save 5% at the building stage, as it will cost way more than this to repair or replace in the next ten years,” she advises.

“Always remember that a roof is only as durable as it weakest component, so select fasteners, flashings and sealing detailing with the same expected service life as the roof. Also specify the installation detailing that makes the roof a fully designed system which will perform for 20 years and more,” Stromnes states.

Wilkinson adds that their Rheinzink roofs need be installed by skilled zinc crafting contractors. “It doesn’t matter if you’ve got the best roofing material, an incorrectly installed roof will reflect badly on the manufacturer”.

Advice to avoid pitfalls:
1.    Know the climate and environment – using incorrect products can lead to roof failures.
2.    Incorrect fasteners can shorten the lifespan of the sheet and affect the warranty.
3.    Ensure that accessories such as flashings match the roofing material.
4.    Check the branding on the reverse side to confirm the specified material.
5.    Always insist on material and fastener warranty.
Courtesy of BlueScope

Designs that push boundaries
When taking on projects outside of the traditional scope, the special design detailing is another factor that needs a closer look as this will play a role in determining a suitable profile, according to Jeffrey.

“Architects are really pushing conventional products to the edge of their design capabilities with fantastic designs such as vast overhangs and curved roofs,” he says. “However, these designs that challenge the performance of profiled roofing products, together with the changing climate conditions and unpredictable weather events, have led to manufactures upping their game by improving product performance over the last few years.  

Full thanks and acknowledgement go to BlueScope, Global Roofing Solutions, Rheinzink and Safintra for the information given to write this article.