Post 307- by Gautam Shah
Roofs as the outer most enclosure system of a building, define the form of an architectural entity. A heavy roof requires equally heavy sub structure, thus creating an effect of ‘solid or monumental building’, whereas a lighter roof system requires a lighter support structure, and seem very delicate or trivial. Roof-structures based on compressive elements are inherently heavier compared to tensile structures.
Roof systems are predominantly Compressive for several reasons. Roofs put up by comparatively non-mobile or stable societies are permanent, static, heavier in weight and well founded to grounds. These buildings have heavy bearing structure with fewer or smaller openings. Heavy roofs have low spanning capacity so interior spaces are small or narrow. The interiors are dark, compartmentalized and isolated from the outdoors. Heavy roof structures are hazardous for earth quake conditions. Construction of a heavy roof requires large manpower, through participation, coercion or money. Heavy roofs are ecologically inferior as there is inherent wastage of materials. Heavy roofs and their heavy support systems, require equally heavy foundation work which is difficult and a time-consuming proposition.
Roof systems are also tensile structures. These are light in weight, and so often demountable and portable. Such structures are preferred by nomadic or transient people. Light roof structures and their lighter support system, both offer free, open and bright interiors. Open interiors have an immediacy with the surroundings. Some structures are large span entities composed of very few elements, so are extremely adoptable to different internal arrangements. These structures unless well integrated with their support system and properly based to foundations are hazardous in wind storms. These structures with better cover material and appropriate pitch can be used in areas with heavy rainfall. These are ecologically very superior as there is inherent economy of materials and require very little foundation work. Execution is fast.
Roofs have many different forms –flat, pitched, vaulted, domed, etc., depending on the available materials and technology, architectural needs, and economic compulsions. Some of the primitive forms of roofs were, Pitched roofs with thatching, Conical roofs of hides, Flat roofs of stone slabs, and Gabled and flat roofs with rafters of dressed timbers. Plants, hides, and stone were the primary materials, gradually replaced with manufactured materials such as terracotta roofing tiles and woven mats. Coatings of primitive waterproofing compounds like tar, pitch, wax and fats continued for a very long period.
In low rain and hot-arid areas like Sind (Harappa) and Egypt flat roofs of heavy clay mass over wood structure were created to form terraces. Tropical countries with seasons of heavy rains had high pitched thatched roofs. Nomadic societies on Mongolia, Indians of Americas and Saharan regions developed demountable and transportable shelter system. These shelters had integrated roof and support system.
Roof systems occur as the outer most enclosure. An inclined roof has higher surface area, compared to a flat roof. An inclined roof has solar gain during part of the day when its inclined side faces the sun. This can be exploited for various locations. Roof forms are designed primarily to deal with the effects of environment. In high rain and snow fall areas roofs are designed for drainage. Roofs are also sloped to enlarge the roof surface area to receive higher solar insolation or sun light for energy conversion systems like heating pipes, solar power cells etc. Roof slopes are oriented to South or North faces, depending on the Northern or Southern hemisphere, respectively.
ROOFS and FLOORS (earlier article here)
SLOPED ROOFS (earlier article here)