The water tank roofs are the brainchild of a former intern, Venkat. It was indeed an immense learning experience for the interns to get to work on this project with the masons who agreed to shift from their mindset of doing conventional building techniques. The construction process for the first water tank saw a few glitches but they were learning lessons for us to draw guidelines of the steps to be followed for the next shell roofs.

For a cluster of three houses at Sacred Groves, a series of 9 organically shaped water tanks were required. The shell design for their roofs is unique. The challenge of the shell roof construction lies in the organic shape and finding the resourceful waste materials to implement this construction technique.

The shell roofs that support the grey water treatment system come on top of the earth-crete walls of the water tanks. The grey water from the houses will flow in between stones that forms the gutter that is formed between the dome and the earth-crete wall. The stones are laid with shade net on top on top of which there is earth fill to grow banana and papaya. The shade net will ensure that soil particles will not enter the gutter and thus makes sure the gutter does not get blocked. The grey water from the houses will be added with EM (Effective Micro organisms) that contains bacteria. These bacteria convert the dirt into nutrients. Plants like papaya and banana will absorb the nutrients, absorb water and also help in cleaning up grey water. This system is repeated at different levels and the left over water is collected in the tenth tank to be used for gardening purpose.
Part cross section of shell roof

The two feet earth-crete walls are marked to hold the steel reinforcement which forms the skeleton of the shuttering for the shell roof. The reinforcement bars are bent to a curvature calculated by AutoCAD drawings. The centroid of the water tank is marked with reference to the points drilled. The reinforcement layer for the bar is made in such a way that after the final masonry is completed the reinforcement bars can be removed from the opening at the centre of the shell roof.

Tetrapack sheets produced from waste plastic forms the second layer. These form a smooth surface to hold a layer of mud plaster which is the third layer. It forms the support for the actual layer of masonry made from waste rubble blocks, and mud plaster is removed from the central opening in the roof, after the shell construction is completed.

Waste rubble pieces form the perfect building material for masonry as they tend to contain small amounts of concrete and stones to counter tension as well as compression. These pieces are laid layer by layer around the opening and simultaneously packed with mortar.

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