Indians are weather-driven people. While good weather cheers us up, bad weather leaves us sulking and cursing. In summers, we long for winters, and in winter when extreme cold freezes our blood, we long for summers. The game goes on. Summers are, however, longer and more taxing and a time when one looks for ways to keep the heat out of one’s home.
One of the tested and tried method of keeping the house cool is to have high ceilings and storey height. Higher storey height means cooler rooms. That’s why storey height used to be 12 to 14 ft in 1950s and 60s. Palatial houses even went up to 20 ft high. These days, however, this figure has reduced to 10 to 12 ft. In apartments, it is less than even 10 ft. Even if one wants to keep a higher storey height, the building bylaws don’t permit it in most urban areas. The alternative in such a situation is to insulate the roof against heat.
Let’s have a look at some of the ways of insulating our house against summer heat:
The roof slab of houses is invariably in RCC these days, As bricks absorb less heat than RCC, some people prefer to use reinforced brick (RB) roofing but such a roofing has many disadvantages and shouldn’t be used. One should choose RCC only and further insulate it by providing a good topping over it. For it, many types of tiles are now being offered by their manufacturers. However, brick tile, which has been in use for the past several decades still remains the best bet. The prevalent method of tile terracing can, however, be modified to provide better roof insulation.
At present a layer of hot bitumen is applied on the roof slab and is covered with good earth laid in slope towards the rainwater pipes. A layer of 1-inch thick mud mortar is spread over the good earth layer that is 3 to 5-inch thick. Chopped straw is added to the mud prepared for plaster, if available. Brick tiles are laid over it in mud plaster. The brick tiles are then grouted well with cement sand mortar and are finally given a flush- pointing treatment.
In the modified method, a 2-inch thick layer of expanded polystyrene, popularly called thermocol is laid over the layer of hot bitumen heated to 180 degree centigrade and pressed into place. The thermocol layer has a density not less than 18 kg per cubic meter. Over the thermocol layer, the good earth layer is laid and rest of the procedure as prevalent is followed. The 2-inch thick layer of thermocol has a significant insulating effect on the roof of the house.
While providing the 2-inch thick layer of thermocol, precaution needs to be taken that the sheet is well pressed over the laid layer of bitumen so that no gap exists between the two to allow rainwater to seep in between them. Rainwater, if allowed to enter below the thermocol layer, gets entrapped there and has a damaging effect on the roof. Also ensure that 16.5 kg of bitumen is laid and spread over an area of 10 sq m. The joints of the thermocol sheets are sealed by applying bitumen with a brush and further, by fixing adhesive tape on them.
The addition of 2-inch thick, 18 kg per cu m density thermocol layer in the tile terracing causes significant reduction in room temperature. The reduction is up to 3°- 4° C and it is a significant reduction. It not only provides respite from heat but also reduces load on your ACs.
Another easy method of roof insulation is the application of heatshield, a heat-reducing product devised by a water-proofing company, on the exposed surface of the roof top of your house. Heatshield is in liquid form, ready to apply and is white in colour. It shouldn’t be diluted by adding any thinner and should be applied with brush after cleaning the surface and applying a primer on it. One litre of heatshield covers around 30 sq ft area. Two coats of heatshield should be applied for reducing the room temperature by 3°-4° C. Its long-term performance is yet to be seen as it is comparatively a new product for India.
Present trend is of providing large-sized windows in homes. These extend almost to the ceiling. Further, the central panels of these windows have fixed glazing while ‘openable’ parts provided in the sides are of very small size. Toughened glass is provided in the central fixed portion to avoid provision of grills and to add beauty to the house. Large-sized fixed glazing in windows invites lots of heat and turns the rooms into virtual ovens during summers if these windows are located in west and south- facing walls of a house. House owners should, therefore, take adequate steps for thermal insulation of window glazing.
The glass chosen for the windows should allow maximum light and minimum heat to pass into the rooms. Such glass is called sun-control glass or thermal-insulation glass. This glass is coated with metallic oxides during its manufacture. It reflects minimum light, thus allowing its maximum transmission. At the same time, it reflects maximum heat radiation thus allowing minimum heat to pass to the room. Many firms have started producing sun-control and thermal-insulation glass. Most of these glasses reflect long wave heat radiation only. One should examine the company brochures and select a glass that is highly reflective to both, short as well as long wave heat radiation.
Wherever the window glazing has already been done with simple float glass or toughened glass, sun-control film should be provided on the glass for thermal insulation. Good quality films resist 99% UV rays, 75% of solar energy and cut the glare. One can choose the film’s colour and shade. One should choose reflective films as these are provided with a thin metal layer and don’t allow the heat to pass. The films are like stickers, having a liner at the back which when removed exposes the adhesive to paste the film on the window panes. While affixing the film, care should be taken that no air bubbles get entrapped behind it.
Double glazing is prevalent in commercial and office buildings these days but is not so popular in the residential sector because of its high cost. In double glazing, a 12 mm air gap is provided between two layers of glass. The outer and inner glasses are 6 mm thick each. The outer face of inner glass is coated with low E coating to minimise heat transmission through the glass. Double glazed windows with low E-coating are quite effective in thermal insulation of windows but suffer from two disadvantages. One, these are very costly and secondly, moisture often crops inside the air cavity and gets entrapped there. This moisture remains trapped for a long time and looks awful. Silica balls are added in the air cavity to soak the moisture but also get saturated soon. Thereafter, only solution to remove the moisture is to replace the double glazing.
Another effective method of roof insulation is to provide under-deck insulation. In this method, a 2-inch thick layer of expanded polystyrene or thermocol sheet is fixed to the underside of ceiling by using rawl plugs and GI screws. The density of thermocol is not to be less than 18 kg per cubic metre. Precaution is taken that no gap is permitted between the adjacent thermocol sheets. This method of insulation is also very effective. However, it should be used only if false ceiling is to be provided in the house. In such a case, GI wire mesh is fixed over the EPS sheets and the surface is finished with POP.