What is Cavity wall?
A cavity wall is a kind of masonry structure; consists of two leaves constructed in parallel to each other, held together with the help of ties or bonding units to make them act as a single unit. The construction of the cavity wall along with advantages and disadvantage are given below.
Ties are the component to hold the leaves of the wall (inner wall and outer wall) together ensuring the stability of the wall. The wall leaves need not be of equal thickness.
As in the name suggests, the wall has a cavity within them, filled with insulating material. Air is the most common insulating material for the walls. Besides, Styrofoam, mineral fibers can be used as per requirement.
The structural performance of the cavity wall depends upon both leaves; therefore, the ties are introduced in the cavity wall. Different kinds of materials are being used as the ties and bonding units since the early development of the cavity wall. Stone, brick, metals, plastics common material to serve the purpose of ties.
Procedure of Cavity wall construction
The use of cavity wall in common in extreme climates; hot and cold for thermal insulation. The cavity wall is also suited for sound insulation and damp prevention. Cavity wall construction is delicate work. The following are the few things to consider while constructing the cavity wall.
- The thickness of each leaf should not be less than 75mm.
- The cavity between the walls should not be too much and less. It would be wise to keep the gap between 50-75mm.
- Weep holes should be provided in the wall for extrusion of moisture.
- Ventilation also should be provided at the bottom and top of the wall, to prevent stagnation of air and humidity.
- Ties are should be placed not exceeding the distance 450mm vertically and 900mm horizontally.
- If the metal ties are being used, rusting should be avoided
- Galvanizing, Painting can be done.
- The few courses of cavity wall at top of the wall are built solid, the base plate is inserted to ensure uniform load distribution to both leaves of the wall.
- The Cavity walls should not be solid below window sills and door jambs damp proof course are to be inserted.
- Mortars droppings, broken building units should be cleared from the cavity and ties at end of each day.
Here is some illustration of the advantages and disadvantages of cavity walls over solid walls.
Advantages of Cavity wall construction
- Cavity walls prevent dampness intrusion through the wall.
- Cavity walls give thermal insulation; it decreases heat transmission from inside to outside and vice versa.
- Cavity walls are best for sound insulation as the velocity of sound is higher in solid.
- Cavity walls are relatively 20% economical than solid walls.
- Internal and external insulation work can be avoided resulting in cost-effectiveness.
- Cavity walls avoid the formation of efflorescence.
- Cavity walls are light in weight-reducing the load in the foundation.
Disadvantages of the Cavity walls
- Highly Skilled manpower is required for construction and supervision.
- Wall ties are likely to get rusted as the outer wall is exposed to water and the replacement of worn-out ties is a tedious job.
- The cavity can act as a breeding place of insects and termites.
- The materials left out in the cavity can keep a hold of dampness making the situation worse.
- Slightly more space is required due to an increase in the overall thickness of the wall.
- Construction defects in the walls can lead to dampness bridging.
I hope this article on “Cavity wall construction” remains helpful for you.
Happy Learning – Civil Concept
Contributed by,
Civil Engineer – Rukshana Shrestha
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