A filler slab replaces part of the concrete in a regular RCC roof with light, local materials – matkas, clay pots, tiles. Same strength, lighter roof.

The structural logic: in a slab, the top concrete handles compression and the bottom steel handles tension – the concrete at the bottom does no structural work. It’s dead weight adding load, cost, and carbon. Replace it with fillers, and the air pockets inside them block heat from entering. The ceiling breathes. The home stays cool without AC.

Architect Laurie Baker popularised the technique in Kerala in the 1960s–70s, and every region found its own filler – Mangalore tiles, terracotta, clay pots, coconut shells, even waste bottles. Today firms like Wallmakers, Biome Environmental Solutions, and Blurring Boundaries build sustainable homes with filler slabs — Biome once used old keyboards as fillers. Less concrete, less cost, less heat.

This is Day 9 of Built Desi – a series on the materials India built itself with, and why we stopped using them. Start from Day 1: Rammed Earth.

I’m Utsav Kamboj, architect and urban designer, documenting How India Builds – the materials, decisions, and stories behind India’s built environment.

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