Multi-tiered roof: A sustainable building element

The roof, on an average, accounts for upto 80% of the radiation received by a building envelope. Traditionally, it is the most pristine element of architectural expression in a building. It probably is now taken for granted, inexpressive flat plane after advent of concrete.

The roof was the trickiest element due to its aesthetic (being most expressive externally), technological (as the spanning element) as well as environmental (as it took direct radiation at the most critical time of the day) obligations. The triple obligations were ingeniously entwined to emerge as a single architectural resolution. The style of a roof spoke of climate in the region, function within the building or even the place on the globe. It acted effectively to manage internal environment.

Numerous strategies adopted for centuries have proven their worth over time. One such strategy was the multi-tiered roof, such as large sloping three-tiered roof of Kerala and Konkan or even sloping and layered roofs of the colonial bungalows as well as institutional structures. Multi-layered roofs with large overhangs protected walls from rain and even Sun. Overlapping layers of the cascading roofs also offered mutual shading sheltering roof surfaces. Slopes also offered direction to the roof with respect to Sun at any given time (except for overhead Sun) leaving leeward sides under shadows. One of the most significant contributions of these roofs was to effectively ventilate the building. By principles of convection, hot air being lighter would rise up and the gaps between layers would effectively escape the hot air out. Also by virtue of sloping roofs, it offered additional volume in the attic, helping create negative pressure to induce upward draft of hot air and guide it outside of the structure.

This idea of a ventilating roof was also very effective in hot and humid climate. Air movement through roofs worked as wind flushing. Not only heat and air but even light was greatly modulated by roof apertures. As a clearstory window, it made central volume brighter and cheerful. Extra volume in colder regions got adopted as attics. Even profile of the inclined roof curving gently upward at the edges, especially in rain prone regions, pushed rain away from the edges protecting walls from being splashed.

Wisdom of this classical architecture was as effectively evident in the local-tribal vernacular roof forms too. For example, Bhungas of Kutch or Thar made houses with conical thatch roof on cylindrical walls. These roofs have large overhangs. In rain prone area, the structure helped protect walls from water and kept the home cool in hot summer conditions. Apart from thatchy overhangs, the roofs have inherent cracks for smoke and hot air to escape, thus an
organic ventilating roof.

In arid zones, urban houses had flat terraces to provide environmental protection and shade. Rajasthani architecture has ably demonstrated elaborate architecture of flat roofs. Nearly room high parapet walls, chhatri pavilions and white lime finished yet richly decorated floor surfaces transformed the external terrace plane into an outdoor room. Parapet contributed in mutual shading, reflective surfaces provided insulation and projecting floor profiles sheltered the walls against harsh Sun.

Sloping or flat roof, fundamental wisdom of large overhang, roof ventilation, surface insulation and diffused illumination through roof apertures are forgotten in present day architecture and consequences of the same can be experienced visually and environmentally around us.