Monthly Archives: December 2014

EFFICIENCY OF DOMES

They can be built on any space without steel reinforcement and centering, with substantial savings in cost and time.

06bgp-green_GFL_06_2234609gThousands of monuments from historic times are still around us, fully or partly standing in good condition. What are the common roof forms of these extant structures? Very curiously, majority of them do not have the flat roof popularly seen today, but have curved roofs in the form of vaults and domes. If they were built everywhere and continue to be stable even today, there has to be reasons for their efficiency. And, they deserve our attention to re-discover this age-old knowledge system.

Dome is the commonly seen round roof form, often seen rising above the wall line. Mostly seen in religious and pubic buildings, domes have always been considered to be among the more elegant and dominant forms in urban skylines. Incidentally, as per Dr. Yogananda, who has extensive study and design of domes behind him, they can be built on any space without steel reinforcement and centering, with substantial savings in cost and time. Lack of skill and the apprehension it generates is among the reasons for not building with domes, so his team regularly conducts workshops, besides actually building domes to prove the point.

The process

If round rings of reducing diameter are kept one above the other, the resulting raised form becomes a dome. To build one without centering, the dome profile has to be segmental and not hemispherical for structural reasons.

First, we need a reference distance to get them all in place, so the dome dimensions are finalised and the centre point on the ground is marked. A long pole on a rotatable pivot is fixed here as a guide, the tip of which becomes the spot for placing the individual bricks. The dome compulsorily needs a ring beam at the base, and if not, needs buttressing on edges to carry the dome load away.

A rich composite mortar with soil, cement and stone dust or any other locally appropriate mix is used to fix the bricks, first in round courses and then one above the other, with the mason standing on the dome itself. Same bricks are tied with thread, and hung across the just placed bricks as counter-weights which prevent the brick from falling until it gets set in place. As the dome nears the top, another ring beam can be placed with skylight or solid surface finishing the top. Unlike the popular belief, domes need not be the last roof, but can be intermediate slabs with such shallow rise that the upper surface can be levelled to get another floor above. Domes tend to echo, though this problem can be solved.

The method of building domes without formwork support is actually simple, though it may appear complex. As such, it is advisable that masons take some training and the building owners consult an expert engineer.

Despite such limitations, masonry domes have been and can be among the most eco-friendly and cost effective solutions for roofing a building.