The Low Cost Roofing Technology with Filler Slab

A roof is a covering component on uppermost part of the building which provides protection from weather primarily against rain. As roofs are just covering components, live loads will not act upon it. Still the common practise is to cast solid RCC slabs like floor slabs to keep the aesthetic view of the structure or building. Now innovative ideas are brought in an economical way without hindering the aesthetic side. One such new generation idea is filler slab.

A Filler slab is a Reinforced Cement Concrete slab that uses filler material embedded in it so that the weight of the slab and amount of concrete used comes down. Pots, Terracotta tiles, Coconut shells and bottles are some of the materials used in the filler slab system. 

The filler slab is based on the principle that for roofs which are simply supported, the upper part of the slab is subjected to compressive forces and the lower part of the slab experience tensile forces. Concrete is very good in withstanding compressive forces and steel bears the load due to tensile forces. Thus the lower tensile region of the slab does not need any concrete except for holding the steel reinforcements together.

Therefore in a conventional RCC slab lot of concrete is wasted and it needs extra reinforcement due to added load of the concrete which can otherwise be replaced by low-cost and light weight filler materials.

There are many advantages by using Filler Slabs like, will reduce the dead weight as well as the cost of the slab to 25% (as 40% less steel is used and 30% less concrete). The filler slabs also result in fewer loads getting transferred to the load-bearing walls and the foundations. The air gap in between the tiles makes it a good heat insulator. Reduction in concrete and steel reduces the generation of carbon which in turn makes the slab construction eco-friendly. If done with proper workmanship, the filler material can be exposed inside the building to create aesthetically good ceiling.

Certain things to be considered while doing filler slabs are that the Filler material should be inert, It should not react with concrete or steel It should be light weight, low cost and preferably locally available as this method is mainly adopted for economical advantage. Size of filler material should be such that it fits in bottom half of the slab and structural grid of reinforcement, material with good thermal insulation properties like clay should be opted to provide thermal comfort inside the room. More care should be given while concreting as there is a chance of displacement of the filler material.

Substantial amount of work on the successful promotion and transfer of this technology was done by Ar. Laurie Baker in South India. It is one place where filler slab has crossed the boundary of research and controlled implementation to being one of the regular options of construction by both government and private sector and also architects and designers have been promoting this technology as this is an  effective low cost roofing technology.

Author

Parvathy Unni

Civil Department