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Understanding Cavity Walls

The term “Cavity Wall” refers to a Cavity Wall is a type of wall construction, where there is an empty gap or cavity left between two layers of brickwork. it’s also known as the Hollow Wall. The gap between the two layers of brickwork is known as the leaf that is inside and the outer leaf. In modern constructions the gap is filled with Cavity Wall Insulation (CWI) or insulative material. This is carried out in construction rather than injecting it like when it’s retrofitted. Buildings with cavity walls was first introduced sometime in the 19th Century and became popular in the 1920s.

Initially , they were built with no insulation. They were slightly smaller, their size is typically between 4 and 10 cm. There are however numerous instances of homeowners who had CWI retrofitted. From the 1970s on, insulation in the cavity became standard during the 1990s, building regulations made it compulsory in new construction.

In the case of a Cavity Wall, the two brick skins are joined by what is also known as Wall Tie. Wall Tie which are usually made of metal. They used to construct with tie-ups made of iron, mild steel or copper, however these materials were susceptible to corrosion. Wall tie corrosion first came to light during the 1960s. Following this, they switched to stainless steel since it’s less susceptible to corrosion and this keeps the structural integrity for longer.

The walls were originally designed and constructed to avoid problems with damp. The cavity was created to keep moisture out of the building’s interior and allows the water and moisture to drain back out of walls through ourepoles. These are tiny gaps in the wall’s external pointing which permit the water to escape from the wall. They are typically placed each one meter on the leaf’s exterior.

Walls made of concrete differ greatly when it comes to handling moisture in a distinct way because bricks are porous. This makes it simple for moisture to move between the exterior and the internal wall creating a penetrative damp problem so in order to stop this the walls must be thicker, meaning they will cost more to construct. They are also less efficient because they do not provide much heat or sound insulation since there isn’t the presence of an air space in the cavity.

It is important to know that CWI can create a damp problem, can contribute more so to the existing damp issue or accelerate the process of the wall’s failure. This usually happens due to an inefficient insulative material used in the cavity as the material does not allow the wall breathe and evaporate excess moisture. The material acts as a “bridge” to carry the moisture to the internal wall creating an issue with damp. However, more modern and natural materials can be utilized which allow the wall to breathe better.


The walls may provide some fire resistance.
They are able to reduce the risk of moisture, condensation build up, and penetrative damp issues.
The cavity wall could reduce the cost of heating an entire building. The air in the cavity acts as an insulation.
They are a good sound-proofing option in comparison to houses with a brick-built wall, reducing the effect of external noise.
In terms of cost, Cavity Walls are cheaper to construct than walls of solid construction because they don’t require as thick.
It protects against efflorescence, which are white marks on the exterior brickwork that form when water enters the wall, leaving crystal salt deposits.
The wall ties are the sole item that joins the two walls together and they are impervious to moisture. Since there is no direct contact between the two leaves of the wall there is almost no chance of moisture getting into the wall. The wall was designed to keep rain from entering the wall and transferring to the internal.

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Cavity Wall construction is more challenging than constructing a solid wall, it requires plenty of supervision in its construction phase to ensure it is executed correctly.
The skill level required is greater for the construction of cavities, which is why expert designers high-skilled masons, skilled labourers are required.
There is always a chance that moisture could penetrate from the external leaf of the wall, and then reach the inside, since the cavities were not intended for filling with fillers.
If the insulative material gets wet, it could lead to cold bridging or thermal bridging. The term thermal bridging refers to the act of heat moving across an object that will be more conducive than the materials around it.
The retrofitting of CWI to a wall cavity can leave unfilled air pockets – creating cold spots in the interiors of the wall, which can attract condensation.
As mentioned earlier wall tie corrosion can also be an issue, and when they are installed with CWI , the outside leaf is colder, which means it becomes less moist. Meaning it can speed up the process of corrosion of wall ties, and there is no way to replace wall-ties with enough.
If you wanted to install CWI, the thickness of it will be restricted by the width of the cavity as they will differ from one building to the next.

CWI issues CWI

For some , Cavity Wall Insulation could be very beneficial, reduction in heating costs and keeping your home warm for longer. However, there are some issues that can arise from retrofitting cavity wall insulation or, if you’ve had it installed previously, you might already be facing problems. The cavity in most homes is intended to function as one, and filling that space with CWI material could end up contributing to the development of a penetrative damp issue.

In the event of a decrease of air moving around the cavity meaning water will be unable to evaporate. If the insulative material becomes saturated it will hold moisture close to the inner leaf, and act as a bridge to allow moisture to travel across the cavity, which can lead to damp issues with penetrative penetration. In addition, it could cause humidity being trapped near flooring joists, causing flooring rot, and eventually flooring failure.

We’ve also witnessed numerous instances of cowboy installers who have failed to install CWI, and due to this, there are a large number of homeowners who’ve ended up with a home that’s less efficient due to the CWI wasn’t installed correctly and gaps without insulation are created in walls, leading to cold spots that result in condensation spots in the interior wall.

The issue can also arise in the event that the building is steel or timber framed, as the cavity is again utilized to prevent moisture from the frame of the building. If this ends up being covered with CWI then moisture is permitted to remain close to the frame and could cause decay and corrosion of the frame which can lead to structural failure.