Cavity wall: Construction, Purpose, Advantages & disadvantages – civilnotebook

A cavity wall is a special type of wall built up of
ordinary bricks or blocks. So arranged to provide within the wall an air space
(cavity) extending throughout its length and height. In the cavity wall two
parallel walls are constructed. These two parallel walls are called leaves,
inner leaves and outer leaves, and the inner wall is called the inner leaves.
Generally cavity walls are also called as Hollow walls.

Cavity wall

            Such a construction is
generally adopted for the external walls of a structure so as to make it heat
& sound proof. Cavity walls are also employed for inner walls where the
rooms are desired to be sound insulated. In the cavity wall, the absorbent materials Rockwool or Mineral wool, Cavity foam insulation, Polystyrene bead are used in the cavity construction wall, and the absorbent materials are
absorbed by the rainwater and rainwater raw draw out through the weep hole.
Weep holes are constructed at the bottom of the outer leaves and through the
weep hole cavity walls are maintained in the humidity. Absorbent material also
insulates the sound and heat. (Thermal)

Purpose of cavity wall:-

    1.      Cavity walls are an economy.

    2.    Making the sound proofing.

    3.    Cavity walls prevent the moisture content.

    4.    Cavity walls also prevent the dampness.

    5.
Thermal insulation.

 

Construction of cavity walls:-

• • • Generally foundation is the same, no need for
      special treatment for the footing construction of cavity wall. Footings are
      done according to the uses and serviceability of the structure.

• • • In the first construction of the cavity wall two
      leaves are constructed at the center of the footing like normal brick masonry
      and the cavity wall will be provided between two leaves of the wall should be
      parallel and uniform thickness throughout its length. It should not be less
      than 5 cm not greater than 7.5 cm.

• • • The thickness of internal leaves and external
      leaves in the cavity wall is 75 mm thickness.[Properties of bricks]

• • • Two leaves may be equal thickness (10 cm each)
      where they are not subjected to heavy load. For non-load bearing walls inner leaves
      are thicker and the outer leaves are less thick compared to inner leaves. In
      case of load bearing wall outer leaves can also be used as load bearing wall
      but cost of construction will be increased.

• • • Cement mortar proportion is 1:4, adequately reinforced
      with hoop iron.

• • • Weep holes are constructed at the bottom of the
      cavity wall in the outer leaves.[Chain Surveying]

• • • Internal leaves and external leaves are connected
      by a links.(metal ties)

• • • Cast iron or wrought iron cramps (called metal
      ties) 20 cm long and 25m X 6mm X section with ends split and fish tailed are
      also used.

• • • Metal ties should be shaped to check the passage of
      crates from the outer wall to the inside of the building.

• • • To prevent subsequent corrosion of metal ties,
      these are embedded in hot tar before use.

• • • Cavity wall is built solid at the courses and at
      the jambs for a length of 10 cm moreover the top three courses under roof,
      arche work, and lintel are also built solid.

Point considered in the construction of cavity
walls.

• • • There should be as little contact as possible
      between the two leaves.

• • • D.P.C. should be provided separately for each leave
      and at floor levels for internal wall.

• • • The thickness of the cavity should be uniform
      throughout (at least 5 cm)

• • • The maximum thickness of the cavity in the cavity
      wall is 75 mm.

• • • Weep holes are always made at the bottom of the
      cavity wall in the outer leaves.

• • • Inner and outer leaves are connected by links,
      metal ties.

• • • Ties to be used should be effective enough to check
      the flow of moisture to the inside walls.

• • • Before use of metal ties embedded in the hot tar to
      prevent corrosion.

• • • The cavity should be well ventilated at the bottom
      to check the accumulation of foul air.[Filtration–Type of filtration]

• • • Jams and lintels should be carefully rendered
      seepage proof preferably by lead flushing.

Advantages of cavity walls:-

    1.      Cavity walls are an economy. Because 20 % less
material is used for the construction of the cavity wall in comparison to the
solid wall.

    2.      Cavity wall gives protection against efflorescence.

    3.      Cavity wall gives protection against fire. Because
it’s fire resistant.

    4.      Good sound insulator. It reduces the effect of
external sound coming into the inner side. And it also reduced the effect of
sound from the inner side to the outer side.

    5.      Cavity walls are good thermal insulation.

    6.      Reduced cooling and heating cost of building.

    7.      Cavity walls also reduce the risk of moisture
condensation.

 

Disadvantages of cavity walls:-

1.      To the construction of the cavity wall highly
skilled labour, mason, expert designer and experienced person are required.

2.      During the construction phase of cavity walls good
supervision is required.

3.      For all types of opening in cavity walls like door,
window etc. Vertical damp proof (D.P.C.) are required.

MCQ’s

    Q.    Cavity walls are also called Hollow walls.