A cavity wall is a type of walls that has a hollow center and constructed with two separate walls for single wall purpose and between them, there is some space or cavity and these two separate walls are known as cavity wall leaves.
The outer wall is called the external leaf and the inner wall is called an internal leaf, and up to 10cm is the minimum thickness of the inner and outer leaf or wall and if it is a load-bearing structure this wall is strong to carry the imposed load safely.
To construct the outer wall of a house cavity walls are used and these walls are constructed in such a way that between the single wall an empty space or cavity is left about 5cm to 8cm.
The cavity wall is constructed for purposes like damp prevention, thermal insulation, sound insulation, etc. Cavity wall also ensures that inside of the building the inner leaf of the wall remains dry and no moisture penetrates.
These walls construction is not a modern concept they have been observed in Roman and Greek structures and still exist. In the united state late in the 19th-century cavity wall constructions were first built and the use of this wall increased rapidly in this country.
Construction Of Cavity Wall:
There are the following steps in the construction of these walls such as;
- Under cavity walls it does not require any footings and just a strong concrete base is provided on which this wall is centrally constructed.
- Like normal masonry two leaves are constructed but in between them minimum cavity or space must be provided about 5cm to 8cm and above ground level the cavity may be filled with lean concrete with some slop at the top up to few centimeters.
- For outer leaf at the bottom with an interval of 1m weep holes are provided. For inner leaf normal bricks are used and for outer leaf facing bricks are used and by metal ties or wall ties made of steel, the leaves are constructed.
- 900mm is the maximum horizontal spacing of wall ties and 450mm is the maximum vertical spacing and wall ties are provided in such a way that from outer leaf to inner leaf they do not carry any moisture. Stretcher bond is provided for half brick thickness leaves and care should be taken without filling the cavity with cement mortar while laying bricks.
- Wooden battens are provided in the cavity with suitable dimensions to prevent mortar dropping in the cavity and on the wall ties these battens are supported & location is reached whenever the height of the next wall tie. Wall ties are provided by removing battens using wire or ropes.
- By predetermining the location of wall ties spacing should be uniform and two leaves should be constructed simultaneously and two leaves separately damp proof course is provided. Weep holes are provided above the damp proof course in case of door and windows.
These walls are also constructed at the door or window openings, in the roof, and in the parapet wall.
Points To Be Observed During Construction:
There are following points to be observed during the constructions of these walls such as;
- Below the damp-proof course level the cavity should be The walls are built solid below the ground level or below the damp-proof course with fine concrete, the cavity should be filled up to 15cm.
- The DPC should be laid to the span of one leaf only under no circumstances.
- Below the wall plate or roofline the upper part of the wall where it ends should also be built solid for two or three courses and to distribute the load over both.
- By means of a timber batten suspended in the cavity the wall ties must be kept free from mortar dropping.
- To permit water to drain away at the bottom of the cavity it is desirable to leave a few vertical joints in the outer leaf open.
Purposes Of Cavity Wall:
There are following purposes of these walls as given below:
From the outer leaf to the inner lead cavity walls reduces the chance of moisture intrusion and dampness is avoided inside the building.
From the outer leaf to the inner face of the interior leaf these walls minimize the transmission of heat and maintaining the thermal insulation of a premise these walls help in it.
For absorbing sound the air in the cavity acts as a cushion and a premise may work as a soundproof zone as a large quantity of external noise gets absorbed within the cavity by building cavity walls.
To prevent the cavity as dampness is not allowed and the inner leaf of the cavity is kept free from the effects of efflorescence because the inner leaf is always a load-bearing wall.
As building a 275mm cavity wall costs less than a 328mm solid wall and on the specific climate of the construction site this measuring data may vary from one place to another.
Before deciding a measurement of a cavity wall one has to calculate the customized details.
Advantage Of Cavity Walls:
There are the following advantages of these walls such as;
- Because of the space between two leaves of cavity these walls give better thermal insulation than solid walls and into the building from outside reduce heat transmission.
- They are cheaper than solid walls economically.
- Because of hollow space between leaves the moisture content in the outer atmosphere is does not allow to enter.
- These walls are also good sound insulators.
- Because of their lesser thickness they also reduce the weights on foundation.
- These walls also prevent the outer efflorescence.
Disadvantages Of Cavity Walls:
There are the following disadvantages of these walls such as;
- For these walls construction highly skilled labor and masons are required.
- During its construction require standard supervision.
- Due to settlement and saturation of cavity-fill the cold bridging problem in these walls occurs.
- Wall-tie corrosion is also a problem is these walls.
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