What Is Cavity Wall? Purpose & Constructional Details

What Is Cavity Wall?

Cavity Wall - It is a wall made of two parallel levels of masonry, separated by a continuous air space. Continuous space is called a cavity. Cavity walls consist of three main parts:

1. The outer leaf which, is the exterior part of the wall
2. The cavity, the continuous open-air space
3. The inner leaf, which is the interior part of the wall

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Purpose of Cavity Walls  

The cavity walls are provided for the following purpose:

1. Damp Prevention - Cavity wall eliminate the penetration of moisture from outer leaf to the inner leaf and thus help keep inside of the building free from dampness. It is made possible because whatever moisture get penetrated through the outer leaf is subjected to evaporation by the air inside the cavity, as cavities are kept well ventilated.

2. Thermal Insulation - The air in the cavity acts as a non-conductor of thermal heat and hence minimise the transmission of heat from the external face of the interior leaf. Thus cavity walls, help greatly in the thermal insulation of the buildings.

3. Sound Insulation - The air in the cavity wall acts as a cushion for absorbing sound, by adopting cavity walls building may be rendered soundproof as considerable external noise gets absorbed in the cavity.

4. Efflorescence - As dampness is not allowed to penetrate by a cavity, the inner wall of the cavity which is always a load-bearing wall is kept free from efflorescence effect.

5. Economy - Cavity walls are found to cast about 20% less than the construction of same thickness solid wall.

Size And Location of Cavity Wall

The cavity between two leaves should not less than 50 mm and not more than 75 mm. The cavity may be sealed or ventilated sealed cavity is more effective for thermal insulation whereas ventilated one is more effective for damp prevention ventilation of cavity may be obtained by using air brick in the outer leaf near bottom and top of the cavity.
                                                                     The cavity may be started from the top of the foundation concrete block, but it is seen that the cavity below damp proof course does not serve any purpose. Hence up to 100 to 300 mm below D.P.C. at plinth level, brickwork in the foundation is generally constructed solid and the cavity may be started only about 150 mm below the D.P.C. level. This 150 mm depth below DPC helps in drawing any condensed moisture below the level of DPC. Damp proof course for the two leaves of the wall is set on an individual basis bye at an equivalent level.
                                                                                                                   The cavity may lead right up to the top of the parapet and converted by copying and D.P.C. It may be stopped levels but D.P.C. must be laid over the cavity.

Constructional Details of Cavity Wall

The cavity walls have two leaves inner and outer with hollows space in between them. Width of the cavity varies from 50 mm to 75 mm. The thickness of the outer leaf of the wall which is usually non-load bearing wall is half-brick. Inner wall is always load-bearing and its thickness should not be less than one brick. The two parts of the wall are connected by wall ties or bonded bricks. Metal wall ties are spaced at horizontal intervals of about 0.90 mm and vertical interval of 450 mm. The wall tie should be arranged in a staggered fashion. The outer wall always in stretcher bond, but it can be constructed in other bonds as well by using brickbats.

Also, read - What is AAC Blocks ?
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