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CURVING THE ROOF, differently

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Flat clay tiles make a hourdi roof easy to maintain, and the aesthetics are stunning.

What is the most critical part of a house – foundation, wall, roof, openings or staircase? The obvious answer is the roof, hence maybe the metaphorical meanings when we say ‘roof over the head’. It is of course, less visible than the walls, hence often gets lesser attention, especially where front elevation looks are more demanding.

While walls enclose the room providing protection, it is the roof that provides the true shelter. Unlike any other element of domestic architecture, here we face multiple issues to grapple with. Immediate thought could be about the structural issues, as to how to support the roof itself. Traditional architecture worked around local materials to solve this issue, while modernity has opened up innumerable options.

People across the societies have felt the need to innovate on roofs, either because there never has been a totally satisfactory design or roofs have had the scope to play with them. While the flat and sloping roofs have dominated at large, all other options have continuously knocked at the door.

Amazing forms

Contemporary architecture using advanced software to generate a profile, computer-controlled manufacturing of components and on-site technology to assemble them all have created some amazing roof forms across the world, with architects like Frank Gehry and late Zaha Hadid leading the pack of innovators. But do they mean in our small town contexts we need to be deprived of them? No.

The Learning Centre located at Salem proves the point. With the passion of promoter Sanjay and involvement of builder Arun, their team has managed to build a magical school building. It’s it not the just the roof which is special here, but the totality of design and building.

As such and with the concept of minimising cement and concrete, the design revolved around mud and clay.

Roofing with clay Mangalore tiles has been around for over the centuries, but it needs to be only sloping due to the interlocking grooves. By replacing them with flat clay tiles, one could create a curved profile. However, placement or direction of the clay tiles is important to ensure smooth curvature and to ensure that rainwater does not clog anywhere.

Typical computer formulae will not help in resolving the S-curved roof which adorns the school building, but only an experienced structural engineer like Ravindranath could resolve it. The structure also has domes, vaults, varied kinds of filler roofs, stone slab roof and such others. As such, the behavioural patterns of roofs need to be studied and equilibrium planned for.

Special attention

Of course, special attention is called for while assembling the roof for labour safety, joint filling and waterproofing the joints. The fabrication also has to be done to precision, lest the blocks may not be seated properly.

Curved clay flat hourdi roofs have advantages other than merely the novelty. They perform better for speedier construction, reduce steel with their lighter weight, ensure different aesthetics as against RCC ceilings and are easier for maintenance.

Be it the roof, wall or the whole building, architecture should not be driven by the idea of fancy, however attractive these new designs may appear to be. All the elements of design and components of construction should together aim to provide a holistic perception and experience.

Go for the hourdi roof

Masonry vaulted roofs, despite being a common historic factor, lost their popularity primarily due to centering efforts and costs. 

Different style: Alternative architecture has successfully explored curved elements in a building.

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!