A barrier to beat the heat
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A roof exposed to the sun can warm up the interiors to uncomfortable levels. Insulating it is the answer.
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— Photo: Vipin Chandran
Double benefit: Roofing material has to be both durable and appealing to the eye.
The roofs of buildings receive the thrust of heat during the day. The construction practices adopted in the country mainly involve reinforced cement concrete (RCC) as the roofing element which is noted for its high thermal conductivity.
If the roof can be protected from heat incidence, the conditions down below can be controlled to a great extent.
When buildings are air-conditioned, the purpose of the system is to maintain a lower temperature than ambient inside the building. If the roof is exposed to solar heat, it will lead to continuous heat inside the building which in turn will add to the A/C machinery load.
Over-deck insulation
In this system, a thermal barrier or insulation is provided over the RCC so that the heat of the sun is not allowed to touch the RCC slab of the roof at all. In this way we can preserve the RCC from getting heated up. Once the RCC is heated up, there is no other way for the heat to escape other than inside the building.
So, even though the thermal barrier is provided under the RCC, as in under-deck insulation, some heat passes through it and heats up the room. This decreases the comfort level of the room.
Advantages
Hence it can safely be concluded that over-deck insulation has its own advantages against under-deck.
The over-deck insulation material should have adequate compression resistance, low water absorption, resistance to high ambient temperature and low thermal conductivity.
The preformed insulation material is further classified as expanded polystyrene slabs (EPS), extruded polystyrene slab, polyurethane/polyisocyanurate slabs and Perlite boards.
The EPS is a light weight cellular plastic foam material composed of carbon and hydrogen atoms and is derived from petroleum and natural gas by-products.
Extruded polystyrene is an improvement of EPS material and comprises beads/globules compressed to form slabs and pipe sections.
The beads are very closely linked to each other so that the material becomes rigid and there are no air gaps between them.
It is a close cells material and a skin is formed on the top which stops water absorption. Polyisocyanurate/polyurethane foam slabs are urethane foam insulation materials having low thermal conductivity, low smoke emission and low water absorption.
Procedure
The application procedure for over-deck insulation featuring preformed insulants include keeping roof surface free of dirt and loose particles, providing a primer and adhesive coat and adhering of insulation with adhesive, taking care to seal all joints between insulation also with a sealant and providing a protective plaster layer with reinforcement.
Unlike preformed materials, the spray-applied polyurethane is applied directly over the roof by spraying. This eliminates the separate fixing procedure and is formed spontaneously when Isocyanate and Polyol are mixed in the presence of a blowing agent to create close cell homogenous jointless insulation cover of the roof.
T. LALITH SINGH
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