Cavity wall is also known as hollow wall because of its structure like hollow inside. It is constructed in two separate walls and in between these walls a little space is kept. This space is work as cavity and it would be fill by some insulating material in some cases. These two separate walls are called as leaves of cavity wall. The internal wall is called as internal leaf and external wall is called as external leaf. These both leaves can be constructed by either AAC blocks or bricks. The size of cavity is keep in between 4 cm to 10 cm. The internal and external leaves should have at least 10 cm thickness. The two leaves are interconnected by metal ties or links as shown in below figure.

Masonry cavity wall | Brick veneer, Brick cladding, Brick

Purpose of Cavity wall

01. Damp Prevention
Cavity walls reduces the chance of moisture intrusion from outer leaf to the inner leaf and thus helps in keeping inside of the building free from dampness.

02. Thermal Insulation
The air in the cavity wall acts as a non-conductor of heat and hence minimizes the transmission of heat from the outer leaf to the internal face of the interior leaf. Thus, cavity walls help in maintaining the thermal insulation of a premise.

03. Sound Insulation
The air in the cavity acts as a cushion for absorbing sound. By building cavity walls, a premise may work as a sound proof zone as a large quantity of external noise gets absorbed within the cavity.

04. Efflorescence Prevention
As dampness is not allowed to penetrate the cavity, the inner leaf of the cavity, which is always a load bearing wall, is kept free from efflorescence effects.

  • The construction cost of the cavity wall is about 20% less than the construction of solid walls. Hence, they are also economical.
  • Cavity walls are fire-resistant.
  • Cavity walls are best for damp prevention than solid building walls.
  • The wall can reduce the cooling cost of the building.
  • It gives protection against efflorescence.
  • They also act as good sound insulators.
  • It requires installation of a vertical damp-proof course to all openings.
  • It decreases carpet area efficiency.
  • Cavity wall construction requires good supervision during its construction phase.

Main three materials are used more often in concurrence with cavity walls.

1. Mineral wool or Rockwool
This is the material which is used commonly for insulation in residential properties. It is produced from an igneous rock which is heated and spun to create fiber material. This is blown into the cavity wall which then occupies the space between the interior and exterior walls of the building entirely. The material also is water resistant and prevents moisture driven by rain which usually gets though the outer leaf of the wall to reach the inside leaf of the building.

2. Polystyrene Bead
Expanded Polystyrene Beads or EPS beads are utilized in the  of cavity walls. These are pushed into the cavity of the walls, which is mixed with an adhesive which sticks the beads together to avoid being spilled outside of the wall. This type of insulation is usually used in narrower cavity walls rather than using mineral wool insulation and is also preferred in some stone built houses or properties.

3. Cavity Foam Insulation
Urea formaldehyde foam was commonly used for the insulation of cavity walls. They usually have the benefit of needing smaller hole sizes to be drilled in the brickwork or the walls. However, not many people use this nowadays. Most people prefer Polyurethane foam as both a cavity insulation material and a material to stabilize the wall structure where the wall ties have been futile, as an option to replacing the wall tie itself. However, where work is done purely for thermal insulation purposes only, either mineral wool or polystyrene beads are the ones normally used.


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