Masonry vaulted roofs, despite being a common historic factor, lost their popularity primarily due to centering efforts and costs. A study by SATHYA PRAKASH VARANASHI

Nature is not made up of straight lines, while buildings are made up of only straight lines. Accordingly, nature can never build the Taj Mahal and we can never construct a banyan tree. Somewhere have we missed out of creator's wisdom or are we destined to be the opposites? Is there a process difference between the two, where nature grows slowly, while humans build fast?

Growing body of literature, research and experimental buildings have told us that we cannot emulate nature fully yet, but are slowly inching closer. Of course, mainstream architecture still continues with straight constructions, but the alternative architecture has successfully explored curved elements in a building. We need the floor beneath us to be flat, hence curved slabs are not possible for intermediate floors, but a curved final roof may be considered to get the benefits of a different skyline for the building.

Masonry vaulted roofs, despite being a common historic factor, lost their popularity primarily due to centering efforts and costs. Their load bearing capacity, however, is surprisingly large, as such we see vaults covering halls as wide as 100 ft. in the Roman Empire. Being both curved like a semi-circular arch and oblong like a half-barrel or tunnel, these roof forms make the site work complex. What if we can avoid centering? Nubian vaults on moveable centering and hourdi vaults offer this choice.

Additional strength

Vaulted hourdi roof is comparable to Mangalore tiled roofs. Flat hollow clay hourdi tiles measuring between 3x9x16 inches and 3x10x24 inches are placed over M.S. sections, where inverted T-sections take the tiles on top. While such hourdi roofs are possible in straight slopes like Mangalore tiled roof, gently curving they give additional strength, attraction and better water proof quality. Both full-curved vaults and half-curved profiles are possible with hourdi roofs, where curve shape can be worked out to avoid trusses up to certain long spans. Surface being curved, we get wedge-shaped joints between two flat tiles, which can be easily packed with water-proof mortar mix to make them water tight. Except for this pointing of joints, rest of the top clay tile surface is left natural, looking earthy red.

A few sample pieces of hourdi tiles should be ready at site, whose dimensions should decide the precise spacing of steel members in the roof fabrication. Curving the steel T-sections need to be carefully done, all to the same curvature, otherwise the tiles may not fit properly. While laying the hourdi tiles, temporary support may be provided to the steel fabrication.

These roofs cost more than Mangalore tiled ones, but are secure, hence can be used for indoors. Incidentally, they are cheaper and much faster than RCC roofs, and can be fabricated to fit even after the walls are done. Tiles can be reused if dismantled and provide the different look that people may be seeking!

(The writer is an architect working for eco-friendly designs and can be contacted at varanashi@gmail.com)