THE IDEA of having a second roof over the house may sound absurd. But a large number of city residents and commercial establishments are realising that it makes sense in more ways than one. A light roof over the terrace acts as an umbrella for the house, offering protection from heat and rain. It also prevents cracks and build-up of algae on the walls and adds useable space to the building without additional tax burden.
There is a variety of light roofing material available in the market. The popular options are Galvanised Iron (GI), aluminium and PVC but new materials such as polycarbonate, fibreglass and polypropylene are slowly catching up. Many architects feel that, despite the obvious advantages, sheet roofing destroys the aesthetics of a house.
Manufacturers are now trying to blunt this criticism by offering sheets in different colours and profiles to suit each house. The latest rage is the GI sheet in tile profile that closely resembles a set of closely-stacked terracotta tiles. Apart from a cladding for the terrace, light roofing sheets are used as awnings and sunshades. They are also emerging as a convenient, cost-effective option for clubhouses, garages, car parks and commercial buildings.
What are the advantages of a second roof? In a concrete structure, the roof absorbs most of the heat that makes life unbearable for the occupants during summer. Intermittent exposure to rain and heat weakens the concrete on the terrace, leading to cracks and small leaks on the roof. Fixing a leaking concrete roof is expensive, messy and often fails to deliver.
A sheet roof reflects a major portion of the heat to keep the inside of the house cooler by several degrees. The air circulating between the sheet and the terrace acts as an insulator, eliminating heat build-up. A spin off benefit is that the whole terrace becomes useable at all times, rain or shine.
Prices and variety
The tile profile versions are costly, with the better brands costing upwards of Tk. 60 per square feet, compared to GI and PVC sheets that are available. Tile profile sheets are galvanised for weather- resistance and durability. Aluminium is another material that is slowly gaining appeal, though the price factor is a major constraint. Both GI and aluminium sheets are now available in coloured- coated versions.
New-age synthetic materials are also making their presence felt in the light roofing market. The latest entrant, polycarbonate, is priced upwards of Tk.100 per square feet. It comes in transparent, translucent and opaque versions and in different profiles.
Builders point out that it needs professional experts to install a light roof, especially if it covers a large area. The sheets are fixed on to a framework consisting of trusses and purlins supported on GI pillars fastened down to the terrace with concrete. In windy areas and on high-rise buildings, the sheets are further secured with an aluminium band called a wind tie to prevent them from lifting. holes.