Correct Answer - Option 4 : (i), (ii) and (iii)
Explanation
Cavity Wall is a wall made of two parallel levels of masonry walls and having a continuous air space, which is called a cavity, in between these masonry walls. These 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
Functions of Cavity Walls: The cavity walls are provided for the following reasons:
1. Damp Prevention - Whatever moisture get penetrated through the outer leaf is subjected to evaporation by the air inside the cavity, as cavities are kept well ventilated, thereby eliminating the penetration of moisture from the outer leaf to the inner leaf and thus help keep inside of the building free from dampness.
2. Thermal Insulation - The air inside the cavity acts as an insulator or a non-conductor of heat and hence minimizes the transmission of heat from the external face of the interior leaf.
3. Sound Insulation - The air inside the cavity wall acts as a cushion for absorbing sound up to some extent. Therefore, they may act as 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 the efflorescence effect.
5. Economy - Cavity walls are found to cost about 20% less than the construction of the same thickness solid wall.