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Vinyl Roofing-A New Approach

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Introduction of synthetic membrane roofing systems in India offers new solutions in terms of technology and design to address challenges of today’s innovative building designs and demand for high durability.

The Indian roofing system predominantly comprises brick bat coba and bituminous coatings and membrane. There are also available spray applied liquid membranes like acrylic, urethanes and polyurea. However, these systems show constraints and limitations as they are dependant on the substrate bonding for long term performance.

In contrast, roofing membranes made of vinyl and other single-ply technologies have brought about a revolutionary change in roofing specification and installation by offering a clean, quick and efficient alternative to built-up roofs with greater design flexibility. The product also offers energy savings from production to re-use. Other inherent advantages include high resistance to impact and puncture, fire resistance, durability against soiling and high temperature resistance.

Manufacturing

Vinyl roofing membranes are manufactured by various methods including extrusion, calendaring, laminating, extrusion coating, spread coating or combination of these methods. The finished product contains polyester or fibre glass reinforcement, vinyl resins, UV light inhibitors, heat stabilizers, biocides, pigments and plasticizers. Polyester reinforcement imparts high tearing and breaking strengths needed for mechanically fastened roofing system.

The sheets are typically manufactured in widths from 4’ to 6-1/2’ and in lengths from 65’ feet to 100’ in a variety of thicknesses, such as 36 mil, 48 mil, 60 mil, 72 mil, 80 mil and 96 mil. Increasing the thickness of the sheet typically improves the weathering properties as well as tensile strength, tear resistance and puncture resistance.

Design Applications

Vinyl roofs are typically white, gray or tan, and hence tend to reflect heat away from building rooftops and at the same time, offer color versatility to match with other building elements, such as weathered copper or brick. Vinyl membranes are designed to repel dirt, maintaining aesthetic appeal and maximizing reflectivity.

Typical applications of vinyl roofing include:

  • Metal deck roofing
  • Roof garden
  • LEED rated Energy efficient roof
  • Re-roofing of old bituminous and tiled roof

The roofing system is designed taking into consideration the roof deck, insulation, slope, local building codes and desired aesthetics. Single-ply vinyl membranes can be adapted to any shape, barrels, domes, steep slopes and large expansive flat roofs. It can be designed to resist wind uplift, structural movement and harsh outdoor elements. Most vinyl roofing membranes are sealed using hot air, which can be compared to welding metal. The process joins two rolls of membranes at the overlap areas (without using another dissimilar material) to create one monolithic layer that covers the entire roof.

The heat-welded, permanently fused seams on vinyl roofing membrane form a watertight seal, and their peel strength can be critical to the roof system’s long-term performance against wind forces. The heat-welding process also makes the vinyl roofing membrane less weather-sensitive during installation than many other roofing systems. A reduction in moisture buildup during installation can reduce the potential for the corrosion of fasteners and steel roof decks. The systems offer a wide range of application techniques such as mechanically fastened, adhered, ballasted and “green” roof systems. Vinyl’s inherent fire-retardant properties provide self-extinguishing characteristics which can significantly reduce flame spread in the event of a roof fire.

Installation

Vinyl roofing membranes can be fabricated in a variety of widths and lengths to meet the exact dimensions of a roof.

Mechanically fastened roof system: Vinyl roofing membrane can be mechanically fastened directly into the structural deck or structural framing in many configurations. Steep slopes or irregular shapes can be easily accommodated. The systems are typically light in weight and, because the membrane is exposed, can take advantage of a smooth or even colorful appearance to satisfy aesthetic needs in the roof design.

Adhered roofing system: The system is typically installed directly over a compatible rigid insulation board that has been mechanically fastened or adhered to the structural deck or another suitable substrate. It is lightweight, smooth-surfaced and flexible to absorb normal structural movement without compromising the system’s adhesion. They are often used on roofs with unusual shapes and forms. Adhesion to the substrate is achieved by using a water-based or low-solvent-based adhesive on both the substrate and the membrane.

Ballasted roof system: The system consist of the roofing membrane attached at the roof perimeter and held in place with ballast. Ballasted systems are suitable when the structure is capable of withstanding the added weight of the ballast. Ballast can be stone, concrete pavers, lightweight interlocking pavers, or a combination of these. The ballasted system often uses rigid insulation board. The board is placed below the membrane in a standard ballasted system or above the membrane in an inverted roof assembly. The ballasted system can be cost-effective due to the minimal need for fasteners and adhesives.

Environmental Advantages

Energy efficiency: Vinyl roofing membranes are known as ‘reflective’ roof surfaces, deflecting sunlight and radiant heat away from a building, helping the structure to stay cool and reducing energy use for air conditioning. Also, roofing membranes are used as a component in “green roofs,” consisting of multi-layer soil and drainage systems upon which vegetation can grow on urban roofs. Green roofs, in turn, improve the energy efficiency of buildings and enhance the look of urban rooftops.

Resource Conservation: The lightweight vinyl roof systems help reduce the need for heavier structural members often necessary to support heavier roof system options. The versatility of vinyl roofing membranes allows it to re-cover an existing roof, providing both performance and financial benefits. A built-up roof can be overlaid with insulation and topped with a vinyl roofing membrane thereby avoiding disposal of a built-up roof in landfills.

Indoor/Outdoor Air Quality: The membranes have also shown to have a positive impact on air quality. Vinyl roofing membranes when installed on multiple buildings in an urban setting can diffuse heat within a city and assist in lowering air-conditioning consumption, thereby helping to lessen smog formation. Additionally, decreases in urban air temperature can substantially improve air quality, since smog is the result of photochemical reactions that are triggered by air temperature increases. In fact, reinforced thermoplastic vinyl roofing membrane has been recognized for its ability to optimize solar-reflective properties. Furthermore, when existing vinyl roofing membranes are removed and replaced, the process releases little or no airborne contaminants. Also, during installation of vinyl roofing systems, fumes and odors are minimized. Because vinyl membranes can be hot-air-welded together, there is less need for high-solvent adhesives to close the seams.

In tropical climate of India, standard light grey colour vinyl roofing membrane of solar reflectance up to 44% can provide 6-8% energy savings for a 10000sqm centrally air-conditioned building.

Recyclability: Vinyl roofing membranes have a long life expectancy of more than 30 years and can be recycled into such second-generation products as speed bumps, parking curbs and asphalt patching material. Nearly all vinyl roofing manufacturers utilize post-industrial recycled roofing scrap which has been generated in their manufacturing processes in their products.

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