Question

why is a small gap left behind the walls while mounting a girder for roofing

Answer 1

Small spaces are left behind the girders mounted in walls for allowing to expand. Usually one end of the iron structure is fixed and the other end is allowed to expand in summer into the left out gap.

Answer 2

The materials expand on heating and contract on cooling.

Explanation:

Majority of the materials have positive coefficient of thermal expansion which means their size increases with increase in temperature. Small gap is left in behind the walls while mounting a girder for roofing because in summers, the material would expand and would occupy that space. If space is not left, it will exert pressure and cause cracks.

Learn more about: Thermal expansion

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