The design behind ventilated cavity filler roof. By architect Sathya Prakash Varanashi

Global warming is happening much earlier than ever predicted, at which rate we may leave nothing for our future generations. While it is mandatory on all of us to reduce our consumptions, wastages, trash generation and such other measures, it is equally important to devise ways of comfortable living without depending upon energy and electricity.

Cavity roofs have been a part solution towards passive cooling, with embedding clay pots, hollow filler tiles and such others. However, during extreme summers even the hollow clay tiles are becoming less effective.

Heat gets transferred through conduction and convection, the former through solid materials and the latter through voids and spaces. When the building terrace receives direct sun rays, it gets heated up and starts to pass the heat downwards into the room below. Even the voids inside the hollow clay filler roof would let heat go through it, for this trapped air also gets heated with the surface heat being very high. In other words, the present day hollow clay filler roofs will let heat transfer through both the processes of conduction and convection, the void being a sealed one.

In case the trapped air inside the void which gets heated up is not sealed, but move across to let cool air in, then the heat transfer would somewhat reduce. This can be achieved by inserting a small length of electrical conduit pipe between the voids of the hollow clay filler blocks, which are embedded within the RCC roof.

Once all the blocks are in place, small length of pipes are inserted such that their ends are within the void of the filler block. It is not a continuous end-to-end pipe, which serves no purpose at all, but short connections between the voids. As the air inside the void gets heated up, it moves along the pipes to equalise the heat all over the filler block. At the edge block, this hotter air moves out of the block itself, while cooler air enters the voids from the other end.

Between the two outside edges of the slab, one would have breeze called windward direction and the other end will not have much air movement, called leeward direction. Air moves from windward to leeward directions, in the process pushing out the hot air accumulated inside all the voids of the filler roof. This would reduce the heat gain inside the room.

The ends are finished with slight bend to block rain water. Pipe pieces should not move so much that their end is within the tile gap which gets filled by concrete, in which case the continuous air movement will get blocked. All that the builder contractor has to oblige is let a few helpers insert the pipes, which is fairly fast. It’s a one-time investment of time and effort, to achieve passive cooling of slightly higher order.

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