Matka is the Hindi word for the earthen pot. It is found in almost every household and is used as a low-cost water cooler. Handmade on the potter’s wheel, these pots have been in use since ancient times, dating back to the Indus Valley and the Harappan times in India, Pakistan, and Afghanistan, and found even in Bangladesh, Sri Lanka and Burma. This 5,000-year-old technology uses a simple evaporative cooling phenomenon — the water finds its way into the pores of the burnt clay earthen shell and evaporates from there, thus lowering the temperature of the water in the pot.
The matkas can be used to build cool roofs for insulation in buildings. Not only is this method low-cost and green, but also energy efficient. The pots are laid inverted on the mother roof, which provides the air pockets. Air pockets or the air trapped in the inverted pots are poor conductors of heat and prevent heat transfer from outside into the building. Not only do the earthen pots function as natural air-conditioners without the aid of electricity, but they also function as a waterproofing layer as no water can penetrate through the pores of the matkas.
How to?
The earthen pots (usually about 35 cm in diameter) are laid closely packed and inverted on the structural roof membrane brushed with cement slurry. The roof surface has to be covered completely with earthen pots without any surface area left out. The gaps between the pots can be filled up to at least half the pots’ height with recycled cement flyash (residue from cement manufacturing process). This is a low-cost, environmental friendly filler that ensures fewer bleed channels and decreased permeability. Broken pieces of bricks, sand or cement mortar can be used too, but recycled flyash is a greener solution. An inverted earthen pot filler roof can have an exposed hollow bottom ceiling for an interesting play of space.
This technology is highly recommended for historic preservation and restoration for adaptive reuse projects as it is least intrusive to historic fabric and is reversible. Earthen pots can be used in wall construction for increased insulation efficiency and enhanced aesthetic appeal. This technology is seen not only in South Asia but also in some warmer countries in the western hemisphere like Mexico.
Advantages of Inverted Earthen Pot Cool Roofs