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There are various factors that determine which kind of roof to use for your house.
CLIMATE
In hot desert-like climates where rainfall is low, flat roofs are very common. Areas such as North-Africa have a lot of these roofs.
A flat roof is not exactly 'flat'. It usually slopes at an angle of 5 to 10 degrees. This angle can not be noticed easily and helps to drain water during cleaning or after rainy weather.
In traditional African societies, communities living in Arid areas of Kenya such as Maasai, Samburu had their shelters made of flat roofs. This is because rain is not common in these areas.
In rainy climates, the roof becomes steep. In snowy regions such as Northern Europe, the roof is very steep [over 45 degrees] so as to drain away snow. In traditional African societies which live in rainy regions such as Kisii, Mount Kenya and Coast, the thatch roof is very steep [over 60 degrees] so as to increase the surface runoff of rain water.
COST
Roofing materials vary depending on the budget.
In Kenya, thatch roof is the cheapest at KES 180 per square meter.
It is followed by Iron sheets. The thinnest grade in the market at the moment is Gauge 32 which costs about KES 210 per square meter. Gauge 30 costs about KES 240 per square meter and Gauge 28 pre-painted costs approximately kes 500 per square meter.
Concrete roofing tiles cost around KES 400 per square meter.
Clay roofing tiles cost around KES 630 per square meter at Mombasa. These have the advantage of being light-weight and since they are made of natural clay with no added paint, their rain-water runoff can be consumed without any health issues as compared to the others which have paint. Paint contains Lead which is harmful to the human body.
Stone coated steel roofing tiles such as Harvey, Decra are in the range of the most expensive and cost approximately KES 1500 per square meter. These are usually gauge 26 in thickness and hence give a lifetime guarantee. Their light weight also gives savings to the timber supporting trusses which will be less than when supporting heavier concrete tiles.
THEME DESIGN AND SHAPE OF THE ROOF
Curved and cylindrical roofs require special types of materials such as copper and bituminous felts. These felts can take the shape of the roof easily.
Copper felt is expensive. This is usually copper in colour when new and turns greenish as it ages.
Hipped roofs are best laid using tiles since with tiles, there will be less cutting and hence less wastage. Some steel roofing suppliers in Kenya can supply curved roofs. Gable roofs can be done using any type of roofing products.
Some buildings such as Highlands restaurant at Afya Centre, Nairobi have glass roofs. These give nice views but are expensive to put up. A square meter of 10mm structural glass costs approximately kes 2,800.
The steepness of the roof can also be used to control cost. The more steep the roof, the more the surface area and hence the more the cost. Some roofing tiles such as Mangalore design require steep roofs to make sure that the rain water surface runoff is fast and hence no leakages.
Recreational facilities such as tourist lodges which require rustic natural finishes will opt for the thatch roofs which can be patterned to various designs.
Frank Gichuhi
Architect.
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Source by Frank Gichuhi