One important item is the weight of the roofing system. Today’s available roofing materials include a wide range of weights. For comparison, let’s look at the weight of one “square” of various products. A “square” covers 100 square feet of roof area.
- ALUMINUM: 40 – 70 pounds
- STEEL: 80 – 125 pounds
- COPPER: 100 – 125 pounds
- COMPOSITE / POLYMER PANELS: 150 – 275 pounds
- FIBERGLASS / ASPHALT SHINGLES: 275 – 425 pounds
- CONCRETE TILE: 400 – 700 pounds
- SLATE: 900 – 1300 pounds
- CLAY TILE: 1100 – 2000 pounds
Why Does Roof Weight Matter?
The weight of a roofing material, when carefully considered, can be a significant portion of your roofing decision.
Weight impacts key areas of overall roof performance
AGING STRUCTURES. As a structure ages, it weakens. Structural lumber may crack and foundations may move. A low weight roof system can prolong the structure’s life and integrity. A case in point is the First United Methodist Church in Sidney, Ohio. This impressive, looming structure had a clay tile roof that was about 80 years old when, at great expense, the decision was made to remove the tiles, clean them, put new underlayment on the roof, and re-install the tiles. Just a couple of years after this work was done, a major beam snapped above the sanctuary. It was unable to handle the weight of the roof.
SEISMIC ACTIVITY. In areas prone to seismic activity, heavy roofing can cause structures to slide off their foundations or even collapse. Lower weight products can be a good choice as much earthquake damage is sustained by structures with heavy roofs.
HIGH WINDS. Regardless of its weight, properly secured roofing materials can meet even the most strict wind uplift requirements. In the case of catastrophic storms, very heavy weight roofing materials pose a huge risk if they become airborne.
FIRE RISK. Many types of roofing materials are designed to resist combustion from exterior fires. However, most home fires start inside the structure. Firefighters are heavily trained in the risks of entering homes with heavy roof systems once the fire reaches the attic. Heavier roofs create a greater risk of collapse that could trap firefighters inside the structure. This means that firefighters have to contain the fire from the outside rather than enter the building and try to stop the fire.
RAW MATERIAL USE. Roofing materials come, in one way or another, from natural resources. The heavier the roofing material is, the more pounds of our natural resources are being consumed in order to create it.
TRANSPORTATION COST. Heavier weight roofing materials require additional fuel for transportation. With a low weight roofing material, as many as 300 squares or even more may fit on a semi-truck but weight limitations can hold that to 20 – 30 squares for very heavy roofing materials.
ENERGY EFFICIENCY. Heavy roofing materials typically have great thermal mass. While this thermal mass can offer some nominal R Value, it also holds heat. This means that summer heat absorbed by the sun can be held by the roof and continue to keep your attic hot even after the sun goes down.
The use of aluminium-zinc coated steel as a practical cladding material is gaining popularity along the coast of Africa.
Bounded by three oceans and the Mediterranean Sea, Africa has a vast coastline of 26 000km. Its deep rivers and natural ports have been historically important trading hubs and remain as vibrant nodes of urban settlement and business.
The populations of this vast coastline are blessed with abundant natural materials for building, but increasingly, as new infrastructure development booms, the use of metal as a practical, durable cladding material is taking off.
The Safal Group is the sole licensee of aluminium zinc coating technology in Africa and sells its coated steel sheeting along 12 000km of this coastline, down the eastern seaboard from Djibouti to South Africa in the extreme south, and up westward to Luanda in Angola.
All coated steels are not the same
Steel plays a huge role in development, but it does have an inherent weakness – when used unprotected and exposed to the environment, it rusts and corrodes. To extend the service life of steel, it is generally protected with a corrosion-inhibiting coating.
The two most commonly used coatings to protect steel are:
- Aluminium zinc coating (AZ) – aluminium and zinc.
- Galvanised coating (GI) – zinc.
The addition of aluminium to zinc in the coating alloy extends the service life of a steel roof by up to four times that of galvanised steel.
Comparison between AZ and GI coatings.
Source: BIEC International Inc., licensors for aluminium-zinc coating technology used by Safal Steel and other Safal Group coating mills in Africa
Made for Africa’s coastline
Aluminium zinc coating technology, developed in the 1960s in North America, enabled coated steel to deliver a service life of decades, even in aggressive coastal conditions. This development revolutionised the metal cladding industry, and is today the most widely used coating technology worldwide.
In Africa this coated steel is branded Zincal and its factory colour-coated derivative is called Colorplus, produced in Africa at three coating mills owned by the Safal Group.
The thicker the coating, the longer is the resistance to corrosion and the longer the life of the protected steel substrate, and a coating of 54 microns on Zincal Ultima gives it corrosion-proof performance credentials which are suitable for coastal areas where only aluminium sheeting was previously specified.
Taking a challenge head-on
In Safintra’s book of achievements, there is nothing better than a challenging project. This includes challenging locations, weather and most of all, the challenge of trying out a new product.
One such a challenge was the recent application of Safintra products at a newly-installed solar array on the Wild Coast.
Saflok 700 roof sheeting was rolled in aluminium 0,8mm material, transported to the location, installed and then over-fitted with Safintra S-5 roof clamps, onto which the solar panels were secured. Forming part of the approved range of Safintra Roofing System components, Safintra’s S-5 clamps do not void the warranties on the roofing material. This proved to be a critical factor in the financial feasibility of the project. To consider replacing part of the roofing system in this location, even 15 years down the road, was not an option. Safintra’s S-5 clamps are warranted for 25 years and have pull-out loads which are unbeaten worldwide.
The Saflok roofing profile has proven its performance as a sealed roofing system many times and aluminium was the ideal material to use in a location within 2km of the Wild Coast’s shoreline.
Another significant challenge was the timing on the project. Within two weeks, the roof sheeting was produced in the Durban plant of Safintra and loaded on a flatbed truck with clips, fasteners and other hardware. The clamps were put through final loading tests in Denver, Colorado.
A Safintra technical expert, as well as an S-5 technical expert from the USA, was present to ensure the correct installation of the sheeting and the clips above it, and the perfect alignment on solar panels on top of the lot.
Day 3: Tuesday
The S-5 clamps were put through final loading tests in Denver, Colorado, and test videos were sent to the client on the Wild Coast by satellite cellphone.
Day 2: Wednesday
Dustin Haddock left Denver, with the still-warm clamps in his luggage, for 20 hours of travelling.
Day 1: Thursday
Dustin was met by Marnitz Benecke of Safintra in Johannesburg for a late flight to Durban.
An early start from Virginia airstrip in a small plane, on site by 10am, finished by 3pm and back on the plane to Durban that evening.
The project was an immense success, and despite the long travelling hours, Safintra congratulated the team – in the Unites States and South Africa – on a job well done.
Bounded by 3 oceans and the Mediterranean Sea, Africa has a vast coastline of 26,000 km. Its deep rivers and natural ports have been historically important trading hubs, and remain as vibrant nodes of urban settlement and business. The populations of this vast coastline are blessed with abundant natural materials for building, but increasingly, as new infrastructure development booms, the use of metal as a practical, durable cladding material is taking off.
The Safal Group is the sole licensor of aluminium zinc coating technology in Africa, and sells its coated steel sheeting along 12,000 kms of this coastline, down the eastern seaboard from Djibouti to South Africa in the extreme South, and up west to Luanda in Angola.
All coated steels are not the same:
Steel plays a huge role in development, but does have an inherent weakness - when used unprotected and exposed to the environment, it rusts and corrodes. To extend the service life of steel, it is generally protected with a corrosion inhibiting coating. The 2 most commonly used coatings to protect steel are:
- Aluminium Zinc Coating (AZ) – aluminium and zinc
- Galvanised Coating (GI) – zinc
The combination of Aluminium and Zinc extends the service life span of a steel roof by up to 4 times that of galvanised steel.
ZINCAL ULTIMA – made for Africa’s coastline
Aluminium Zinc coating technology, developed in the 1960’s in North America, enabled coated steel to deliver a service life of decades, even in aggressive coastal conditions. This development revolutionised the metal cladding industry, and is today the most widely used coating technology worldwide. In Africa, this coated steel is branded Zincal, and its factory colour-coated derivative is called Colorplus, produced in Africa at 3 coating mills which are owned by the Safal Group.
The thicker the coating, the longer is the resistance to corrosion and the longer the life of the protected steel substrate, and a coating of 54 microns on Zincal Ultima gives it corrosion-proof performance credentials which are suitable for coastal areas where only pure aluminium was previously specified.
Who says it isn’t possible to have the best of both worlds? The look and feel of a traditional tile roof with the GREEN credentials, thermal efficiency, cost saving and lightweight properties of steel – It is possible with Safintra Roofing’s unique profile – Versatile.
Safintra Roofing celebrates its twenty first anniversary this year and has marked the event with a series of new product launches – amongst them the launch of the Versatile 5 profile, a wider version of the company’s Versatile 4 profile.
Use of this profile has exploded onto the South African market and particularly in the province of KwaZulu-Natal, where it has been used on a number of Department of Public Works developments. Tafadzwa Togarasei of leading Durban Architecture firm, DGIT Architecture explains: “I think the popularity of the Versatile profile can be attributed to a number of factors. Firstly, its aesthetic appeal. The beauty of this profile is that it indeed gives you the look of conventional roof tiles. More and more emphasis is being placed on the environment and sustainable building. Steel roofing is by far the most environmentally friendly option available. It is also a fact that in construction time is money. If you have a high quality product that meet standards and saves you time, on procurement, installation and maintenance, then that product is bound to be a winner. This product also enables us to lower the roof structure costs. Its availability in sheet form allows us to make use of fewer trusses, sometimes getting away with half the trusses that would have been required when using conventional roofing tiles. Transport costs are also reduced because a large quantity of sheeting can be delivered in one single delivery. Improved metal coating technology, such as Aluminium-Zinc coatings ensures that our clients have a quality maintenance free product with a superior lifespan.”
DGIT Architecture has specified the Versatile profile on a number of KZN Developments, specifically for the Department of Public Works. These developments include the Department of Education’s Empangeni Rail (Richem) Secondary School and Birdswood Secondary School in Richards Bay. The company has also specified the profile on a number of projects for the Department of Health.
Safintra Roofing’s National Marketing Manager, Sally Stromnes: ”We are extremely proud to add the Versatile 5 profile to our already extended range. We have had excellent reviews from our customers and feel that as more emphasis is being put on designing buildings that conform to environmentally high performing buildings and building materials, the use of steel will escalate. Apart from its obvious economical and environmental benefits steel roofing is also perfectly suited to the harvesting of rainwater, which we believe will become an area of key focus. Going forward, we as a company are committed to providing environmentally friendly solutions to the building industry with innovative products, such as Versatile 5”.
Today's trend for sustainable designs that reduce environmental impact is helping drive the metal roofing market to new heights. Understanding the engineering concerns fundamental to the proper design of metal roofing will enable specifiers to serve the long-term interests of their clients, and reduce liability for all concerned.
In large-span metal roofing applications, concealed fix roof systems are the logical choice – they are fixed to the purlin with a clip system, and are not pierced with any fasteners. The clips serve two purposes – they circumvent the need for holes in the sheet (which prevents the possibility of leakage through the perforation) and they allow the roof to expand and contract in a sliding movement over the clips.
Because the sheets can slide over the clips, they can be rolled in long lengths which can thermally expand without restriction. If the sheets were positively fastened through the sheet into the purlin, the fasteners would take the brunt of the force of expansion, and would tear larger holes in the sheet, or shear off. Consider that coated steel expands at a nominal 1mm per 1m, and it is apparent that a sheet of a mere 15 m will move by 15mm in heat. It is common best practice to not install a pierced fix sheet in lengths of more than 15m for this reason. Over 15m, a pierced fix sheet should be end lapped to allow for thermal cycling.
A concealed fix system allows sheets to be rolled in continuous lengths up to 120m or more. The lack of end laps further helps reduce the risk of leaks.
In these applications, with the size of investment concerned, engineering performance of the roof “system” is critical.
The first distinguishing characteristic of a concealed fix roof is the profile, which is both aesthetic and functional. For low sloped roofs, one is looking for a defined rib, with a wide deep pan to deliver excellent water run off at slopes as low as 2 or 3 degrees. The height of the rib is important as it also provides structural strength, acting rather like a mini I-beam.
Of equal concern is the design of the clip, as this is the “anchor” securing the sheet to the sub structure and holding it down in high winds. The material and thickness of the clip helps determine its inherent strength, which in turn helps to determine the minimum wind-uplift resistance requirements for a particular roof.
The overall “system” design defines the manner in which the clip locks into the sheet profile. The clip should engage every rib of the profile to prevent wind cushioning under the unsecured rib, and distorting the sheet off the clip. Generally, the more ribs that are secured with a positive clasp holding it to the purlin, the stronger the wind uplift resistance. If not positively secured, the ribs should be shaped to provide a strong and stable interlock with the clip at every point.
The system must be able to withstand the foot traffic and loads imposed by the installation of HVAC units, rooftop photovoltaic (PV) systems, or other utilities.
As a profession, you should demand full technical details of the system you intend to specify – and request technical support throughout the installation itself.
Safintra is proud to offer this service free of charge to its customers, from 7 branches countrywide.
With a contemporary design, Safintra’s Trimflute® metal roofing profile is both visually appealing and cost-effective.
A visually stunning and cost-effective metal roofing profile, Trimflute® is unique to Safintra South Africa and is now available in the Gauteng market. It has a subtle square fluted profile with a contemporary visual appeal, ideal for both roofing and cladding applications.
The Trimflute® roofing profile is especially cost-effective when used as side cladding on large industrial projects which have Saflok concealed fix or similar profiles on the roofing.
With a wider pan than any other square-ribbed equivalent, it delivers more than almost 10% cost advantages over both IBR roof sheeting and wider pan profiles such as Widedek.
Its wide pan has excellent water handling performance and the extra wide sheet, which provides over 1m effective cover after lapping, makes it highly cost-effective for budget-sensitive projects.
An ideal roofing solution for industrial, commercial and institutional buildings, this profile can be rolled in any coated steel or in aluminium.
The striking Govan Mbeki Sports Centre in Port Elizabeth, designed by Adendorff Architects & Interiors, features Safintra’s Trimflute® profile extensively for both roofing and side cladding. Apart from adding to the aesthetics of the development, the product was selected due to it being an economic choice.
Sally Stromnes, marketing manager for the Safintra Group, says: “South African architecture is right up there with the best the world has to offer, not only in its design, but also for its innovative use of steel for its functional benefits.
“Our built environment professionals and end-users have caught up with the environmental upside of using steel – its excellent thermal properties, its strength to weight benefits, and the fact that it is cost-effective, durable and completely recyclable. Add the good looks of a really elegant profile that is visually distinctive and metal sheeting demonstrates real value in both design and function.”
Safintra South Africa
Tel: 011 323 6300
The Safintra Group recently opened two new offices in Bloemfontein and Windhoek
Metal roofing manufacturer, Safintra, recently opened two new sales offices in Southern Africa. The new offices, situated in Bloemfontein and Windhoek, intend to help the company offer localised support to its customers wherever they might be.
Besides providing sales and technical support to customers in the Free State, the Bloemfontein office will also cover the Northern Cape. The Bloemfontein office boasts a showroom area that will be used by architects, engineers and contractors as a reference centre for product specification information and specialist installation advice.
The Safintra Group also has operations in ten other countries in the(delete) SADC, Southern and Eastern Africa including Mozambique, Zambia, Malawi, Angola, Tanzania, Kenya, Uganda, Ethiopia, Rwanda and Burundi.
Safintra Roofing & Steel
Tel: 011 823 4027
Fax: 011 823 4288
Today's drive to design buildings that reduce environmental impact is helping drive the metal roofing market to new heights.
Most large roofs are concealed fix roof systems (also called secret fix systems). In principle, they provide some common benefits:
The sheet is fixed to the purlin with a clip system. The sheet hides the clips completely, providing a neat, watertight and no-holes roof, which eliminates the risk of leaks.
Metal expands and contracts at about 1mm per 1m. The clips allow the sheet to thermally expand over the clip in a sliding movement, so very long lengths of continuous sheeting can be installed with no end laps, thus providing further weather tightness.
However, the secret from a performance point of view is not that the sheet is secured by an unseen clip, but the engineering of the clip, and its fit with the profile of the sheet. Aside from profile itself, it is the clip designs that distinguish concealed fix metal roofing systems from each other.
One of the biggest dangers with concealed fix roofing is the wind-uplift performance. No two roofs are the same, and most roofs experience several different areas of wind pressure, whether negative or positive pressure. The material thickness of the clip (gauge) helps determine its inherent strength, which in turn helps to determine the minimum wind-uplift resistance requirements for a particular roof.
3. Value engineering
For all roofing systems, energy payback is derived almost exclusively from R-value, and R-value is derived almost exclusively from insulation. A high-performance metal roofing solution is among the best ways to protect that investment. Once a customer understands how much of his R-value investment is lost, once water penetrates the insulation, the added protection provided from a high-performance roof becomes apparent.
In the realm of roof performance, reducing up-front costs for short-term savings inevitably leads to increasing costs and liability down the road. Learning to analyze the bottom-line benefits of rooftop longevity is critical to specifying appropriate metal roofing solutions. The performance-to-cost ratio will vary with every roof specified, and can only be identified through a comprehensive review of several factors, including:
- How long will the client own the property? Since metal roof systems can significantly outlast most non-metal alternatives, property owners who intend to hold on to their buildings longer will reap the largest rewards from metal's life-cycle costing advantages.
- How disruptive will eventual restoration and re-roofing be to the building's occupants? The installation of a metal roof is odor-free, cleaner, and more environmentally friendly than hot-applied systems. However, installing metal systems can present logistical concerns, especially for high-rise buildings with limited access. Although freight elevators can typically carry materials needed for non-metal systems, for metal systems, large cranes may be necessary to haul longer panels to the top of the building.
- What is the intrinsic value of the property under the roof? The higher the value of the property occupying a building, the easier it is for building owners to rationalize the higher initial costs of metal systems.
- What is the customer's existing budget? If price were no object, we'd all be living and working under roofs of copper, zinc, or even titanium. Regardless of the desirability of long-term solutions, short-term budget realities sometimes prohibit lasting solutions. When a customer's initial budget will not accommodate the costs of a premium metal, innovative financial products such as leasing may be considered. Equally relevant is how soon additional money will become available. It may make sense to install a low-cost alternative on new construction, when budgets are strained, if seven years down the road money will become available for installing a more lasting metal roof system.
- How important are aesthetic considerations, given the roof's location and the building's function? Aesthetic versatility is probably the single biggest reason that owners opt for metal roofing. When aesthetics are a major concern, metal roofing offers added value.
- How likely is it that the owner will follow through on routine maintenance? Generally speaking, metal roofing requires less maintenance than non-metal systems, which may need more frequent re-coating, fresh graveling, or aggressive restoration to maintain resistance to ultraviolet (UV) radiation and weather.
- How frequently will the roof need to be accessed due to HVAC, rooftop photovoltaic (PV) systems, or other utilities? Although metal systems withstand foot traffic as well or better than non-metal roofs, roofs that require a lot of penetrations for HVAC or other appliances are not ideal candidates for metal roofing, as previously explained (see introductory section of this article on the advantages of metal).
This article is part 3 of a series on sustain-ability in the built environment, aimed at professionals, specifiers and owners looking to green building best practise. They focus specifically on the role played by metal roofing and cladding systems in creating better buildings.
Detailed installation methodologies for insulated roof spaces are often over-looked at design stage. As a result the insulation performance may be negatively affected during the on-site installation process, and not achieve prescribed R-Value’s stipulated in the SANS 10400XA standards.
Of key importance, it is imperative that insulation maintains its full design depth throughout the roof assembly in order for it to achieve its R-value. Compression of insulation compromises the R-value & thermal performance of the material. It also increases thermal bridging along purlin lines.
Factors such as cost, aesthetics, thermal performance & combustibility all play a major role in the selection of an appropriate insulation material for a project.
Rigid insulation boards & flexible insulation blankets are the two most popular types of insulation used in commercial roof assemblies in South Africa.
- Rigid insulation boards generally cope better under compression but as their specified depths increase so do the associated costs, and increased risks with long fasteners and system instability.
- Flexible blanket insulation installed over purlin will be subjected to considerable compression along the purlin lines if the outer weather sheet is not elevated. Suitable spacer systems should be employed in these instances to prevent or reduce compression.
There are various forms of spacer systems available in South Africa.
Continuous spacers or ‘packers’ are available in a number of forms such as Timber, XPS or Steel. They are secured directly to the purlins in continuous lengths on top of the insulation blanket which is draped over purlin.
- Packers will cause compression at the purlin but allows the blanket to regain some loft between purlins by elevating the weather sheet.
- It is necessary to compensate for this loss in overall R-value by increasing the depth of the specified insulation blanket and packer accordingly. (See table)
Mechanical spacer systems form the backbone of site assembled roofing systems where warranted thermal performance is required. They eliminate compression of the insulation blanket and take the guesswork out roof assembly performance.
- Lightweight structural steel bars (acting as purlins) are mechanically locked into each other to create the lengths required.
- The bars are supported by brackets, which are available in a variety of heights to accommodate varying blanket thicknesses. The support brackets create a defined cavity for the insulation material and keep fasteners within safe working lengths. Specific loading requirements are achieved by varying the support bracket centres.
TABLE: R-Value’s achieved by 135mm Glass Fibre Insulation Blanket using various Spacer & Packer options:
For further information contact Safintra:
www.safintra.com / www.safintra.co.za
Branches in SA : Johannesburg, Durban, Cape Town, Nelspruit, Polokwane, Port Elizabeth, Bloemfontein
Further operations in: Namibia, Zambia, Mozambique, Malawi, Tanzania, and East Africa.