@ ahsanonline: In 2012 / 13, the market price for jumbolon board (From Diamond foam) and polyurethane (from several companies) one inch thick was around Rs 38 per square foot. Jumbolon board can be ordered in 1, 2 or 3 inch thickness. If you are placing a large order, prices come down. Secondly both products are from the petroleum industry. Prices vary according to petroleum prices in the market.
@aa78: You must keep in mind that, assuming there are no windows, 70 percent of heat in a room on the first floor, is being transferred from the roof. The rest 30 percent comes from the outer walls. So logically speaking, concentration should be on blocking that 70 percent of the heat transmiited from the roof.
Windows are another big source of heat gain into the room. In our weather conditions, bedroom windows should be sized as small as possible, specially those facing the sun in summers. And windows should be raised atleast 3 feet from floor level. It is hardly 2 months when the weather is nice and you want to sleep with windows opened. However, our architects emphasise on placing large windows all around the house, which become a pain in the neck for people who live in those houses.
It is time for our architects to start studying heat transfers and apply that science in their projects which turn out to be practical ovens.
Once you have laid jumbolon board on the RCC slab, you proceed with the usual vapour barrier i.e polythene sheet, mud and rooftiles. You shouldnt be leaving the jumbo or polyuretane uncovered and exposed to the weather elements. Birds will peck it up in a couple of years. I dont know why birds love eating it.
My double glazed windows have argon gas filled up inbetween to reduce heat transfer. But they dont help much in reducing heat transfer when sunlight falls directly on them. Your two story high windows if they are facing the sun, would turn the lounge into an oven even if you use triple glazings with LOW-E glass. Glass in any case is a conductor. In summers you wont be able to use it despite energy bills rocketing up. I have two different TV lounges in my house. One TV lounge is for winters where the sun shines for about 7 hours during the day. It warms up the room so much that we dont require a heater for the evenings. The second TV lounge is for summers where windows are protected from summer sun keeping the room comfortable without airconditioning in April May and mid june without even using an air cooler. We only switch on the AC when it gets humid after mid june.
While you are planning for a central airconditioning system, do also consider a third duct for Air cooler ventilation. I have a duct syetm for cooler which keeps the entire house comfortable during april and May at just 300 watts / hr. If you are running a central air conditioning system for a one kanal insulated house, you would need something like 8 tonnes of airconditioning meaning 100,000 btu/hr. And just think of the generator size that will be required to run the AC plant. You must be a pretty rich man to do it. People like Mian Mansha have switched on to air cooler solutions at their homes. The central Ac system for homes is not something very practical in our local enviornments, specially with unending load shedding.
Studies shows that 70% of heat loss/gain from roof conductance is stopped by a one-inch thickness of spray-in-place urethane foam or Jumbolon Board. The second inch of spray-in-place urethane stops about 80 % of heat loss, and the third inch stops about 95% and so forth. And 6 inches would stop something like 98 percent heat gain / loss. According to studies, urethane thicknesses beyond four or five inches are practically immaterial. In very hot climates experts use three inches for most of residential constructions.
If your last question is about difference in energy savings I can tell you that in this season, our air-conditioners have not been switched on. The air-cooler is doing an effiecent job keeping the entire upper floor cool and kids havent complained. Last year my maximum bill was Rs 14,500 when ACs were used. But do keep in mind that we have these new Inverter based ACs which run at 50 percent of the cost of a normal AC.
So when designing a new home, all concentration should go on making it an energy effiicient home rather than going for italian granite flooring. Your home should not be a showpiece for showing off to your friends and family. It should be a place where your can live comfortably without having to pay monthly bills of Rs 70,000 or more.