Metal Cladding: How To Get The Best From A Metal Roof

Published courtesy SAMCRA

In making the decision to have a metal clad roof one must remember that the most important functions of a roof cladding system (profiled cladding plus ancillary items and fasteners) is to provide a weatherproof membrane followed by aesthetic appeal, however, aesthetic appeal is invariably the governing consideration.

PROFILE:

The first step is to choose a profile (geometric shape) from the two main categories, pierce fix or concealed (secret) fix that best suites the aesthetic and service performance requirements of the building.

 Pierce fix profiles are those where the cladding is anchored to the supporting structure by a fastener that passes through the cladding, the head of which is permanently exposed. Corrugated and box rib are the most common forms of pierce fix profiles. These profiles are not suitable for flat roofs (less than 5°) generally it is recommended that corrugated be limited to a minimum slope of 10° and 7,5° for box rib.

The length of individual sheets is limited to between 10 to 13m due to transport constraints. This, however, eliminates the need to provide for thermal movement. We strongly recommend that both side and end laps be sealed with a reinforced butyl based sealer strip and that side laps are stitched as per manufacturer’s recommendations.

Concealed fix profiles have unique anchoring devices which are contained within the profile and are therefore not exposed to the elements. They also allow for unrestricted thermal movement of the cladding. These profiles can be used on slopes as low as 2°, moreover, they can be rolled on site thereby eliminating the need for end laps. These profiles should never be end lapped which means they are not suitable for in-plane rooflights.

An often overlooked component of cladding systems are the flashings, most leaks emanate from undersized and/or poorly fitted flashings. Whilst the basic design of flashings is universal to all profiles their dimensional proportions vary considerably and we recommend the cladding manufacturer’s standard designs for the respective profiles be adhered to. The two flashings that cause the most problems are the valley and counter flashings. Valley flashings are to have a return, similar to that on a counter flashing, along the full length of their longitudinal outside edges which are overlapped by the cladding, this is necessary to eliminate the formation of a capillary siphon.

Counter flashings have to be independent from head and sidewall flashings, the reason for this is the differential thermal movement between the flashing attached to the cladding and the counter flashing which is anchored into masonry. Under no circumstances is the counter flashing to be mechanically connected to any other flashing.

A similar situation arises with gable and barge flashings on concealed fix systems where sliding connections are required for the attachment of the flashing to the roof cladding. Sliding connections are also required for the attachment of headwall and ridge flashings. Most manufacturers of concealed fix cladding systems supply matching sliding connectors. Under no circumstances are paint-on membranes to be used as a substitute for metal flashings.

Fasteners are to be in accordance with the cladding system manufacturer’s specification and the requirements of SANS 1273 which requires that the durability of the coating on the fasteners and washers, together with that of the sealing gasket, is equal to or better than that of the cladding.

BASE MATERIAL:

The second step is to choose the material from which the cladding is to be roll-formed together with the finish, ie metallic or colour coated. Traditionally metal cladding is formed from metallic coated steel and less frequently from aluminium, stainless steel, titanium zinc or copper, all of which perform differently in a given environment. With coated steel there is a choice between galvanised and 55% aluminium / zinc (ZincAL, Zincalume, etc) both with a colour-coated option with finishes ranging from 30% gloss to matt and textured. Aluminium is also available with a 30% gloss painted finish.

Whilst galvanised is the cheapest option, it is, with a few exceptions, the most vulnerable to corrosion both from the environment and rainwater runoff from other metallic, painted or glazed (including glass and plastics) surfaces, whereas the 55% aluminium / zinc is vulnerable in highly acidic and alkaline environments (pH less than 4 and greater than 9), plus areas of intensive animal farming together with runoff from copper or lead.

All coated steel products must not be in direct contact with stainless steel, copper or lead. Please note that metallic coatings are available in a range of thicknesses and that in general durability is proportional to thickness, ie the thicker the coating, the longer the corrosion protection. When selecting the base material it is vitally important to consider both the macro (area or region as a whole) and micro (adjacent area surrounding a building) environments. Under no circumstances are solar heaters and PV panels to be installed on uncoated galvanised surfaces.

MAINTENANCE:

An important aspect that is regularly overlooked is maintenance, particularly in coastal and highly polluted areas where the regular washing, on a quarterly basis, of surfaces not washed by rainfall is necessary to preserve the protective coatings and compliance with warrantee conditions. We recommend an annual inspection of roofs to check the condition of the surface, attachment of flashings and in the case of pierce fix systems, the condition of the fasteners and their sealing gaskets. In all cases, the regular removal of debris is important as plastics and vegetative matter block drainage systems. In addition, accumulated vegetative matter accelerates corrosion of surface coatings, including painted ones.

INSTALLATION:

In order to ensure the best performance from a cladding system, we strongly recommend that it is installed by a competent, well-trained and experienced roofing contractor. A good starting point is to establish if a prospective contractor is approved by the manufacturer of the chosen system.

Professional flashing – the key to leak-proof roofing

Professional flashing – the key to leak-proof roofing

Flashings for all applications: “The fitting of flashing is key to the professional finishing of any roof,” says Terry Thorp of Roofline

When one constructs the roof on a building, it is always something of a milestone as it signals that the structure is nearing completion. However, once the roof sheeting, tiles or shingles have been secured to the trusses, there’s one task that is crucial to the longevity of the building, namely the manufacture and professional installation of leak-proof flashing.

In South Africa, building standards are not as tightly regulated as they are overseas. This means that, sometimes, some contractors may not apply quite the same attention to detail when finishing a roofing job. In South Africa, building standards are not as tightly regulated as they are overseas. This means that, sometimes, some contractors may not apply quite the same attention to detail when finishing a roofing job. Flashing is often one of the final jobs at the end of a long contract and, for this reason, with informal builders, the fitting of flashing might not always get the attention that is required.

“If you hire a professional roofing company, this contractor will understand the importance of fitting both sheeting and flashing to the highest professional standards,” says Terry Thorp, general manager of the Johannesburg-based roofing company Roofline.

A professionally installed flashing will prevent water wicking back under the roof sheeting and will protect the fascia boards, and ultimately the roof structure. Rain leaking past poorly fitted or incorrect flashings will allow the ingress of water under the sheeting. If the roof trusses are timber, water leaks and seepage can, in a relatively short time, give rise to dry rot which is invariably expensive to repair. Conversely, if the roof trusses are steel, corrosion will weaken the overall roof structure, particularly if the building is near the coast. And then water leaking onto ceilings and walls will create unsightly damp damage which will require yet more repairs.

A serious problem with an incorrectly fitted flashing is the damage is often happening out of plain sight. By the time the property owner realises that something is amiss, substantial damage may already have been done. Many property owners tend not to look upwards and scrutinise flashing and gutters with any frequency. However, by the time that parts of the roof start failing and breaking away, the incorrectly installed flashings will have already given rise to substantial repair bills.

Regarding flashings, what is absolutely vital is to choose the correct profile to suit the type of roof that is in place. “At Roofline, we have the specific equipment needed to manufacture any type of flashing profile in lengths to suit particular applications. Flashings have a number of different profiles depending on whether the flashing is intended for an apex, ridge, gable, side- or a head-wall. Then there are quite specialised fittings where one flashing intersects another – for example, valley-to-ridge flashings or where you have an apex flashing joining a sidewall flashing. With each of these due attention has to be paid to the careful fitting to ensure the jointing is leak-proof,” Thorp continues.

Thorp emphasises the importance of using the services of a professional roofing company particularly when fitting or repairing flashing. “In addition, if you have any doubts about the state of your roof, it is worth the relatively minor expense of calling in a professional roofing inspector as a precaution which might save you the expense of re-roofing your entire building,” explains Thorp. Roofline has been operating successfully for 35 years and has a vast reservoir of experience and expertise in all aspects of roofing. It is fully capable of tackling the very largest roofing jobs such as factories and shopping malls, but is sufficiently flexible to tackle much smaller contracts in the domestic residential sector with the same level of professionalism.

“Should anyone have a question or issue regarding roofing or flashing, we at Roofline would be happy to consult in order to derive an optimal solution,” Thorp concludes.

There’s no beating an original

There’s no beating an original

Secunda Mall
Photo: Gareth Griffiths

By Gareth Griffiths

Over decades, ZINCALUME® has become a household name within the building industry. When specifying premium high performance metallic coated roofing and cladding materials, this original and trusted brand remains the roofing material of choice for specifiers, says the manufacturer.

First made in the late 1970’s, ZINCALUME has a long and distinguished pedigree, having been constantly improved over time. Manufactured and marketed by BlueScope, a reported 28 million tonnes of these zinc-aluminium coated products worldwide have been sold since inception – as verified by the Zinc-Aluminum Coaters Association (ZAC).

The 55% Al-Zn technology is licensed internationally by BIEC International Inc., a BlueScope subsidiary. In certain countries, the technology is marketed as GALVALUME®. In the mid 2000’s, the acrylic surface resin applied to coils of the product at the factory was upgraded, yielding significant advances in performance and formability.

A registered trademark of BlueScope Ltd, ZINCALUME steel was developed in association with Bethlehem Steel in the USA and perfected by Australian scientists at the Port Kembla research laboratories in New South Wales.

The choice of roofing material can affect the amount of solar energy that enters a building, affecting climate control inside the building and the comfort of occupants. To mitigate against heat ingress, ZINCALUME steel has an attractive, shiny appearance designed to keep heat out by limiting solar absorptance. All roofing products are subject to weathering, however, BlueScope’s product will stay brighter for much longer than alternatives, providing approximately twice the thermal performance of other commonly used materials such as weathered galvanised steel and fibre cement/asbestos.

ZINCALUME steel continues to deliver strong thermal performance throughout the life of the product. ZINCALUME is also extremely easy to form and work with”, says Hanekom. “It stays brighter for longer and due to its lightweight steel character. It is the architect’s dream material for curves and shapes, having been formed into a variety of curved surfaces. A good example of this is the roof over the departures terminal at Cape Town International Airport, completed in time for the 2010 FIFA soccer world cup and impressively shaped like an aircraft wing. Viewed from the air, this gives a stunning example of how versatile this product is.

The ZINCALUME roof at Cape Town International Airport is a stunning example of how versatile this product is.
Photo: Gareth Griffiths

The corrosion-resisting benefits of the product are considerable, and a special AZ 200 (both sides coated with 200 g/m2 of Al-Zn coating) version is available for use within the 5 km distance of the sea or in areas where there is a strong industrial fallout.

Because the metallic coating consists of 55% aluminium with the 43.5% zinc (the balance being Silicon), on a minimum coating mass both sides of 150 g/m2 in total, the user gets a highly effective degree of sacrificial anodic protection over the steel substrate meaning that the product may last at least four times longer than conventional zinc coated steels. ZINCALUME steel exhibits a more complex coating structure with both aluminium- and zinc-rich areas. The zinc-rich area provides excellent sacrificial protection, while the aluminium-rich area provides durable barrier protection. It is the combination of these two characteristics that make this unique product durable and effective against corrosion.

All this means that a special corporate warranty of performance can apply when product is fitted in an approved way”, adds Hanekom.

Mbombela Stadium
Photo: Grant Duncan-Smith

Noteworthy projects

ZINCALUME has been used extensively throughout South Africa on a number of high profile projects.

BlueScope customer, Clotan Steel expertly formed ZINCALUME into its Craft Lock profile in use at the Secunda Mall, as specified by architectural firm, LP Architects. The double-story mall was completed late in 2013.

Other examples of projects have included the Mbombela Stadium, Maponya Mall, Soweto, various integrated housing projects and more recently the roof over the massive Pepkor Distribution Centre in Hammarsdale.

Pepkor Distribution Centre, Hammarsdale Photo: Reinhard Swanepoel

If the good name of your practice is on the line, make sure our brand name is on the steel. Look for the brand that identifies the long lasting guaranteed performance of genuine ZINCALUME by BlueScope. It’s stamped on the underside of the roof sheet. Why risk your reputation by using generic Al/Zn coated steel when you can enjoy peace of mind by using genuine ZINCALUME steel?” he asks.

BlueScope Steel Southern Africa (Pty) Ltd

T: +27 21 442 5420 Arno.hanekom@bluescope.com

E: Arno.hanekom@bluescope.com

W: www.bluescope.co.za