A kind of roofing, once popular for commercial and industrial purposes, is now making its presence felt in residential sectors as well. Depending upon the design and style, metal roofing is available in different materials, such as galvanized steel, metal with naturally oxidized finishing, copper and aluminum with pre-painted finishes.
The short construction time is the single largest advantage of metal roofing, which has caught the fancy of Indian building industry. Also, metal roofing innovations have virtually eliminated rust and corrosion worries. Available in variety of profiles and systems, the roofing product combines with glass panels or polycarbonate skylights to offer an international look. Or, if desired, the stone coated metal roof made by attaching stone chips with an acrylic film can offer a feel of more traditional roofing.
The commonly used roofing of corrugated galvanized steel is durable and because of its zinc coating, is resistant to rust. Blends of zinc, aluminum and silicon-coated steel like zincalume, galvalume are also as strong as galvanized steel and are increasingly being used in modern architecture. Internationally, copper roofing is used as accents over bay windows or on dormers to add a touch of elegance. Its advantages include is high malleability, easy installation and life span of more than a hundred years. Zinc roofing is also soft and malleable like copper and is mostly installed in standing seam. Another long-lasting metal is aluminum which is lightweight and corrosion-resistant and has high natural reflectivity and emissivity. Girish Dharachar, General Manager, Umicore India Pvt Ltd adds, “Aluminum is very commonly used in India for roofing applications in different product forms like composite panels or solid sheet. While, zinc is very malleable and can be easily bent for flashings that cover and overlap corners giving a superior finish. Titanium zinc mostly used as a single skin though most expensive offers properties like no maintenance, 100% recyclability and zero VOCs.”
In addition, the advent of longrun roofing (in place of overlapping 3m-long sheets) and the invention of high strength steel coil, has made steel roofing products cut weight and waste and become lighter than earlier conventional products. The new high strength steel coil is about twice as tough (tensile strength) as the softer steels previously employed, meaning thinner gauges can be used. This dramatically cuts the amount of steel needed and makes for a much lighter product. This lighter product is not only more durable because of improved Zincalume® substrate and paint systems but easier to transport and needs less framing to support.However, playing a major role in sustainable design is the aluminum roofing. Being light weight and malleable unlike other forms of roofing, it does not require structural reinforcement and is durable & energy efficient. Moreover, aluminum has high recycle rate as it can be recycled with very low energy consumption almost indefinitely. Aluminum also prevents rapid growth of black mold, mildew and algae, can withstand wind, hail, rain, fire and rot better than any other roofing materials. Some advanced aluminum roof materials also come with heat saving chips to cut down energy consumption significantly. Initial cost of aluminum roofing is higher compared to other common metal roofing materials, but considering its zero-maintenance, energy efficiency and natural no rust characteristic which does not need expensive paint, it is deemed economical in long run.
A roofing product to meet the requirements of thermal comfort is the double skin metal roofing systems. These composite panels essentially comprise profiled sheet on the weather side and slightly ribbed plain sheets on the inner side with PUF/ Rockwool insulation core to reduce the heat ingress and noise transmissions. For example, Lloyd Insulations India Limited offers combination of its LloydDeck and Lloyd Klip Fix for roofing in buildings. As per company, LloydDeck double skin roofing systems are commonly used for weather tightness where reasonable efficient building envelopes are required. Likewise, metal roofing system from Kalzip, a part of the Corus Group, can accommodate various acoustic performance requirements by incorporating other layers such as high density insulation, acoustic boards and flexible membrane. The system provides increased sound reduction performance and improved sound absorption. The advantage of these composite panel roofing are not only its insulating properties but also high load bearing capacity at low weight.
As untreated metal roofs absorb and retain heat, different types of coatings are used on metal panels like anti-rust, waterproofing and heat reflective. They are mostly made of materials such as epoxy and ceramic. Flexible UV stable epoxy coatings are designed to prevent corrosion and withstand ponding water. It is especially suited to applications where moisture content may prevent the use of other coatings. Most ceramic coatings are made from regular paint mixed with ceramic beads as an additive. They add heat reflective characteristic and reflect 75% to 85% of solar radiations. Organic coatings provide aesthetic finish to Galvanised/ Zincalume and architectural polyester coating such as Modified Polyester and PVF2 coatings are also available Oils are sometimes applied to copper to preserve the natural color and metallic tone of copper alloys. The most popular oils are Lemon Oil, U.S.P., paraffin oils, linseed oil, and castor oil used once every three years or five years.
As per a study by the Oak Ridge National Laboratory, USA, installation of reflective metal roofing can save up to 40% in summer cooling energy costs while highly emissive metal roofs can reduce urban air temperatures by as much as 12 ° F. As shown in the figure on the right, the basic, unpainted metal roof reflects much of the solar radiation usually absorbed by the building roof. The pre-painted or granular coated metal roofing system not only reflects solar energy but also cools by re-emitting most of the absorbed solar radiation. Whereas, a highly reflective and highly emissive painted or granular-coated metal roof is optimal for reducing energy consumption and can actually re-emit up to 90% of absorbed solar radiation.
Although, with the growing popularity a range of high performance metal roofing products from different manufacturers are now available in India, aluminum and steel remain the preferred choice of material owing to easy availability and cost-effectiveness. Tata Bluescope Steel Ltd. offers Lysaght®system with Klip-Loktm mechanism that is particularly suitable for situations where long lengths need to be roofed and clad. The system combines fluted pans with a lock-action rib design and has concealed fastening. This means the roof sheeting does not need to be pierced and the ribs make the profile stronger.
According to Hindalco, their roofing product Everlast aluminum sheets never rust and remain leak proof as they are made from pure aluminum alloys in contrast to Galvalume in which the base metal is steel coated with the mix of Zinc and aluminum. The sheets are available in color coated option and can be naturally bent to a curvature. Some of the other companies like Multicolor Steel, Metco Roof Pvt. Ltd, Era Building Systems Ltd, Proflex Systems and Colour Roof India Ltd. (CRiL) also provide advanced metal roofing systems.
An innovative patented roof system from Umicore Building Products, USA is VMZ Adeka. The panels are based on small pre-formed Quartz-Zinc and Anthra-Zinc elements featuring a unique locking key for faster installation. The roofing is suitable for all sizes of flat surface roofs and offers aesthetics of diamond shaped surface pattern and transverse line of offset joint.