Foundation, Concrete and Earthquake Engineering

Cavity Walls

Two walls with a 5 cm to 8 cm comprise a cavity wall having cavity between them. The outer wall also known as outer leaf, consists of a 10 cm (half brick) thick wall and the inner wall is sufficiently thick and strong to carry the imposed load safety. The minimum thickness of the inner wall is restricted to 10 cm (half brick). The provision of a continuous cavity in the wall efficiently prevents prevents the transmission of dampness to the inner wall.


The advantages of cavity walls may be summarised as below:

1. They have good sound insulation property.

2. The layer of air in the cavity being non-conductor of heat reduces the transmission of heat from the external face to the internal one and as such cavity walls are best suitable for a tropical country like India. Tests have revealed that cavity walls have 25% greater insulating value than solid walls.

3. As there is no intimate contact between the two leaves except at the wall ties (which are of impervious material), there is no possibility of the moisture travelling from the outer leaf to the inner.

4. They are economical.

Locating Cavity:

The cavity should start near ground level and terminate near eaves level in case of sloping roof or near coping in case of flat roof with parapet wall. The cavity should preferably start 15 cm below the damp-proof course level. This has the advantage of draining any condensed moisture below the level of damp-proof course. Similarly, to prevent infiltration of moisture, the bottom of cavity should lie at least 15 cm above the out side ground level. The damp-proof course for the two leaves is laid separately, although at the same level. This is necessary to continue the cavity below damp-proof course. The cavity is kept fully ventilated by providing air bricks in the external wall immediately above damp-proof course. The air bricks should be kept 90 cm apart. Similarly, air bricks are provided near the top of the cavity.

Wall Ties:

The two walls are tied together with metallic or terra-cotta ties to obtain structural stability. They are spaced 90 cm apart horizontally and 30 to 45 cm apart vertically in staggered positions.

1 comment:

  1. Cavities walls ,yes, make sense regarding Wall Damp Proof Membrane