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Light-weight & Energy-efficient Roofs

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Roofing systems that can meet energy efficiency and longevity standards as also impose lesser load on the structure are becoming popular among owners and designers alike. Sapna Srivastava takes a look at the wide choice of light weight materials available for roofing a building, ranging from metal, plastic and fabric to innovative thatch & tiles and newer forms of solar roof covering.

Through careful choice of roofing materials, architects are making an effort to reduce the cost of construction, demand on the natural resources as well as building materials that fills up landfill space. The manufacturers too are responding to the evolving environment-sensitive initiatives and have introduced products that overcome the shortcomings of older roofing materials and meet the demands of modern building techniques.

For instance, the solar reflectance and infrared emittance of a metal roof can now be engineered to meet the climate requirements of the building. The metal roofs with oven-cured and pre-painted organic coatings incorporate new “cool pigment” technology that offers high total solar reflectance and high infrared emittance even with darker colors. In addition, emissivity as high as 90% can be achieved for painted and granular coated roofing. This cool metal roofing typically has a minimum recycled content of 25% and is 100% recyclable at the end of a long, useful life. The roofing comprising lightweight steel, aluminum, copper, zinc, stainless steel and titanium in a wide variety of finishes, colors, textures, and profiles can be used for steep-slope, flat and low-slope applications. The architectural metal roofing available in vertical standing seam, corrugated, tile profiles and horizontal panels can simulate the look of standard shingles, wood shake, slate, and tile or can have a coating including, various paint finishes or aggregate stone finishes for aesthetics and durability.

Most metal roofs are among the lowest weight roofing products available and last over 30 years with minimal maintenance. The low weight places fewer demands on a building’s structure making metal roofing an excellent choice for retrofit projects and in locations prone to seismic activity. Thomas Hornfeldt, Senior Vice President, Special Steel Sales at Rautaruukki Corporation (Ruukki), Finland gives an example, “Traditionally the building industry believes that heavy is good and safer. However, this notion is changing. For example, in Stockholm, Sweden, a stadium is being built with retractable high strength steel tubes roof. The use of tubes brought down the weight of the structure by 585 tonnes. Since the weight of the roof went down, the rest of the arena could also be made simpler with lighter structure.”

Similarly, roofing membranes made of vinyl and other single-ply technologies have brought about a clean, quick and efficient alternative to built-up roofs with greater design flexibility. Due to its relative light weight and compactness, vinyl roofing membranes are eco-friendly to produce, transport and install at site. Typically light in color, vinyl roofing membranes also deflect sunlight and radiant heat away from a building, helping the structure to stay cool, reducing energy use for air-conditioning. In terms of recyclability, some vinyl roofing membranes can be recycled into second-generation products while, the manufacturing itself utilizes post-industrial recycled roofing scrap generated during the production process.

A lightweight alternative to glass for skylights, canopies and barrel vaults is the polycarbonate plastic panels. Thin UV-resistant coatings applied to polycarbonate plastic when extruded, offer enhanced protection for performance and aesthetics. Similar product, translucent fiberglass-reinforced polyester (FRP) panels bring in soft, diffused natural sunlight into a structure and have fiberglass insulation between the inner and outer skins to provide thermal efficiency. Polycarbonate roof sheets are manufactured by the process of extrusion and are also called transparent steel due to their high impact resistance and glass like clarity. Nitin Mehta, Managing Director Flexituff Industries explains, “Solid polycarbonate sheets available in clear and tinted variants are generally chosen for applications where vision through the glazing medium is necessary whereas, embossed/Textured polycarbonate sheets with a texture on one surface provide light diffusion and prevent see-through vision. Multiwall sheets, as their name suggests are hollow or fluted polycarbonate sheets which have an air gap between two thin walls. Besides these products, the solar control polycarbonate transmits a controlled amount of visible light and reflects the larger part of solar heat radiation simultaneously, resulting in cool lighting within the covered area and avoiding heat accumulation.” In fact, the cellular, hollow or multiwall polycarbonate sheets are a product of choice for atria, vaulted skylights, canopies, awnings and large skylight domes in commercial areas. These sheets provide excellent economic value and are available in clear, tints and opal white variants. It is impact resistant, lightweight and can be cold curved to suit any roofing application for commercial, industrial or residential usage.

A roofing concept that could be used for exterior as well as interior applications is tensile fabric shading. For exteriors, the tensile fabric acts as a light weight roofing for structures while in interiors it can be stretched as a false ceiling. The exterior application of the fabric in particular, offers dynamic forms combined with structural stability and functionality. Widely used in airports, stadiums, mall atriums, restaurants and as skylights and porches in residences, fabric allows natural light in the interiors sans heat and glare, resulting in a bright daylight atmosphere and warm ambience. Rahul Jindal, Managing Director, Loom Crafts Furniture (India) Pvt Ltd, says, “The fabric structures are engineered to meet the requirements of most building codes and standards worldwide. It provides speedy installation or relocation as an alternative to conventional construction. The system utilizes fabric membrane panels placed under high tension within a non-corroding aluminum substructure. These tensioned fabric structures are available in widths 30ft to 200ft by any length and shape.”

The commonly used fabric materials for tensile roofing are polyester coated with PVC or fiber glass coated with PTFE, suitable for a variety of shapes and spans. Custom-made fabric structures are engineered to meet structural, fire safety and weather-resistant requirements and with their aesthetic free-form design offer designers, the potential to create an instant architectural landmark. The other benefits include energy efficiency as no artificial lighting is required during day, mobility due to easy installation and demounting and cost that is about half of what a traditional roofing would cost. For structures where high performance in thermal insulation is desired, the newer single layer low- E membrane fabrics are now being used. The fabric has a low emissivity treatment on the backside with a high concentration PVDF coating on top surface for UV resistance. The product has a lower solar factor, meets flame retarding standards and is a 100% recyclable textile.

An innovative light weight roofing option for resorts and vacation homes is the synthetic thatch made from recycled plastic. The roofing is not only similar in looks to natural thatch but is as environment friendly. The versatile thatch roof panels do not require skilled artisans and can be conveniently installed on a preexisting roof as well. The roofing apart from being no maintenance is structurally stable and UV resistant. Vashistha Shah, Director, Eurasia Polychem adds, “We provide Synthetic thatch roofing panels which are widely used in hotels, villas and bungalows to give the natural thatch look. The roofing does not attract insects, rodents or birds and does not need replacement for almost ten years”. Lightweight concrete roof tiles too are being used in projects to enhance the aesthetics of the traditional architectural style in a cost effective way. The tiles with smaller profiles and thickness compared to conventional tiles can be easily installed on most conventional roof systems without additional support and deliver the lowest life cycle cost than other materials. The energy efficient tiles made from natural materials like sand, cement and iron oxide pigment remain cool in summers and are highly weather resistant. Likewise, synthetic roof slate tiles manufactured from post industrial and post consumer polymers called ACE compound, is durable and environmentally safe material for roofing. The extremely lightweight synthetic slate weighs about 1/4 of the weight of natural slate per square meter is also fade resistant, maintenance free and 100% recyclable.

Keeping in sync with the innovations in other segments of roofing, solar roof covering too is transforming into a more aesthetically pleasing material. The recent advances in flexible thin-film photovoltaic materials allow manufacturers to easily integrate photovoltaics directly into the metal roofs of buildings. The novel adhesive solar thin films can simply be peeled off of their backings and stuck to the roofing material. They offer a flexible and lightweight solar roofing option that is easier and cheaper to install than conventional crystalline-silicon solar cells and can also be applied to curved roof designs. Solar shingles too work like the conventional larger solar panels but again are much more aesthetically pleasing. Instead of a huge array, solar shingles integrate easily with existing roof shingles via bolt-on panels and do not add extra weight on the structure below.

A product under development by The Speciality Group, Australia is composite and lightweight solar roofing in sheet form, from UV cured polyester resin Prepreg. The technology aims at building integrated photovoltaic product, where the roofing material itself has solar cells embedded into it. The Speciality Group, CEO, Daniel Leipnik explains, “Building Integrated Photo Voltaic (BIPV) technology produced in panel form replaces the need to install a roof and then heavy solar panels on top of the roof separately. Now the roofing will already have the solar cells embedded into it. This means a one step process of installation, more coverage of photovoltaic material, greater overall solar energy generation and far less installation cost.”

Similarly, Bayer MaterialScience has engineered two innovative rooftop solar modules, a photovoltaic module for producing electricity and a solar air collector that captures the sun’s heat. “The two modules don’t just use solar energy, they simultaneously serve as roofing and in the case of the air collector, even intelligently increase insulating performance.” says Jens Geschke, who manages the innovative Solar segment at Bayer MaterialScience. These new solar designs provide for multifunctional roof elements that are attractive & inconspicuous and weigh only half as much as a conventional tiled roof.


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