Cavity Wall

R. Barry (Author of the Construction of Building) claims that cavity wall is a common design element for almost all small structures outside walls.

Between 1920 and 1940, the constructional anatomy was most prominent.

It was built as cavity walls consisting of an outside leaf of bricks or blocks, an interior leaf of bricks or blocks, and a continuous hollow area in between.

Cavity walls were popular in ancient Greece and Rome, but they weren’t used in modern architecture until the 18th and 19th centuries.

Even at this time, it was uncommon to build cavity walls, which typically featured two leaves of masonry joined by headers that crossed the cavity.

In the second half of the 19th century, the employment of metal ties to join the two layers become commonplace.

At the start of the 20th century, the practice became more widespread.

What is a Cavity Wall?

A cavity wall is created by joining two independent walls into one wall while leaving a space or void between them.

The term “leaves of a cavity wall” refers to these two distinct walls.

The exterior wall is referred to as the external leaf, and the inside wall is known as the internal leaf.

A hollow wall is another name for a cavity wall.

Cavity walls are built with a gap between every single wall, also known as a cavity.

Purpose of the Cavity Wall:

  • Remove water from a system of walls or windows using weep holes at their bases.
  • Cavity walls assist keep the interior of the structure dry by lowering the likelihood of moisture invasion from the outer leaf to the inner leaf.
  • Due to the air’s role as a heat non-conductor in the cavity wall, there is less heat transmission from the outer leaf to the internal face of the interior leaf.
  • Sound is absorbed by the cavity’s air, which acts as a cushion.
  • Since moisture is not allowed to enter the cavity, the inner leaf of the hollow is always a load-bearing wall maintained free from the effects of efflorescence.

Types of Cavity Wall Insulation:

1. Rockwool or mineral wool:

Rockwool or mineral wool

Mineral wool often known as Rockwood is the cavity wall insulation material most typically used in residential buildings.

It is manufactured from igneous rock that has been heated and spun into fibre.

This fills the space between the exterior and interior walls of the building by being blown into the cavity wall of the structure.

Rain-induced moisture intrusion normally penetrates the outer leaf of the wall and enters the internal leaf of the building but can be stopped by the material’s water resistance.

2. Polystyrene Expanded Bead:

Polystyrene Expanded Bead

Beads made of polystyrene or expanded polystyrene are used in the cavities of cavity walls.

These are inserted into the wall cavities, which have been combined with an adhesive to keep the beads together and reduce the possibility of their overflowing outside the walls.

Narrower cavity walls typically employ this kind of insulation.

It is the preferred insulation material, as opposed to using mineral wool insulation.

3. Cavity Foam Insulation:

Cavity Foam Insulation

Foam made of urea formaldehyde was typically used to insulate cavity walls.

This insulating material typically has the benefit of easy insertion, which is accomplished by drilling smaller holes in masonry or wall cavities.

But right now, it is not a preferred choice.

Most people choose to replace the wall tie itself with polyurethane foam that can also be used to stabilize the wall structure in places where wall ties have proven ineffective.

Mineral wool or polystyrene beads are the materials optimal when work is done solely for thermal insulation purposes.

Construction of Cavity Wall:

Cavity Wall

Cavity walls often don’t need footings underneath them.

A solid concrete base is provided on top, where the cavity wall is built centrally.

The construction of two leaves is similar to that of regular masonry, but a minimum gap between them must be allowed.

Lean concrete with a top slope up to a few centimetres above ground level may be used to fill the hollow.

For the outer leaf, weep holes are placed at the bottom, spaced 1 m apart and for the inner leaf, regular bricks are utilized, and facing bricks for the outer leaf.

For cavity wall leaves, different masonry is additionally used.

The metal ties also known as wall ties that hold the leaves together are often constructed of rust-resistant steel.

The maximum horizontal and vertical wall tie spacings are 900mm and 450mm, respectively.

The wall ties are designed so they don’t transfer any moisture from the outside leaf to the inside leaf.

There are various wall tie shapes.

Stretcher bond is available for leaves with a half-brick thickness.

Additionally, English bond or Flemish bond-type constructions are offered for brick thicknesses of one to several.

Care should be used when laying bricks to avoid putting cement mortar in the gap.

Wooden battens with the proper dimensions are placed in the cavity to stop mortar from spilling inside.

When the height of the next wall tie site is reached, the battens are removed using wires or ropes, and wall ties are provided.

These battens are supported by wall ties.

It is best to concurrently build two leaves.

To achieve equal spacing, wall ties should be installed in a pre-set location.

Two distinct damp-proof courses are offered for the leaves.

Weep holes are offered above the damp-proof course for doors and windows.

Advantages of Cavity Wall:

The benefits of hollow walls over solid walls are as follows.

  1. Cavity walls offer better thermal insulation than solid walls because the air-filled area between two leaves of cavity walls limits heat transfer into the building from the outside.
  2. They are less expensive to build than solid walls.
  3. Due to the hollow spaces between the leaves, moisture from the exterior atmosphere cannot penetrate.
  4. They so also guard against moisture.
  5. They are also effective sound insulators.
  6. Since of their thinner construction, they help lighten the load on the foundation.
  7. Additionally, outer efflorescence is stopped.

Disadvantages of Cavity Wall:

The Limitations of hollow walls over solid walls are as follows.

  1. For the construction of well-built cavity walls, highly qualified masons, labourers, competent designers and implementing workers are needed.
  2. During the construction phase, cavity wall construction needs to be carefully supervised.
  3. All openings must have a vertical damp-proof course installed.
  4. There is always a danger that moisture will get inside, regardless of the insulation material.
  5. The carpet area’s efficacy is decreased.
  6. Masons and highly skilled personnel are needed to build cavity walls.
  7. Require the usual oversight while it is being built.
  8. Additionally required for it is a vertical damp proof course.

FAQ- Cavity Wall:

Q1. How do I determine if I have a cavity wall?

Take a look at a window or door on one of your house’s external walls: If a brick wall is thicker than 260mm, it probably has a cavity.

A thinner wall is presumably solid.

Though they may be even thicker, stone walls are often sturdy.

Q2. How durable are cavity walls?

All blown-in cavity wall insulation should last up to a century if no damage is done to it.

The figures should be comparable, lasting up to 100 years for alternative insulating techniques utilized during construction.

Q3. Is there an alternative to a cavity wall?

Although it might seem a little off-topic, loft insulation is a fantastic substitute for cavity wall insulation.

The common misconception that wall insulation is the technique to stop heat loss is untrue.


We may reasonably conclude the explanation that installing cavity walls as exterior walls will help you control moisture incursion in your home.

The benefits of a cavity wall extend to both thermal and acoustic insulation.

Construction of a cavity wall demands expert labour and careful management.

If you can construct it properly, it will be beneficial for both you and your house in terms of comfort and maintenance.

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Hello and welcome to House Modify! I am Rahul and I am passionate about everything related to design, decoration and renovation. I am a serial renovator, currently working as a civil engineer. Take a look around, leave a comment and don't forget to subscribe to my emails so you don't miss out!

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