Cavity Walls are a type of wall construction in which there is an open space or cavity that is left between two brick layers, it’s also known as an Hollow Wall. The gap between two brick layers is known as the leaf that is inside and the outer leaf. In modern constructions , the gap is lined by Cavity Wall Insulation (CWI) an insulative material. It is applied in the course of construction, not injecting it like when it’s retrofitted. The construction of structures with cavities was first made available around the turn of the century and was widely adopted in the 1920s.
At first, they were constructed without insulation. They were slightly smaller in size, the in general, the size of the cavity is between 4 and 10 cm. There are however many instances of homeowners who have CWI retrofitted. Since the 1970s, insulation in the cavity was standard, and in the late 1990s, building regulations required it in new construction.
Within the case of a Cavity Wall, the two brick skins are joined by what is called the Wall Tie which are usually constructed from metal. The wall was constructed using tie made of iron, mild steel or copper, but these materials were susceptible to corrosion, and wall tie corrosion first became apparent in the 1960s. From there, they started using stainless steel because it is less susceptible to corrosion and which keeps the integrity of the structure longer.
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The walls were originally designed and constructed to avoid problems caused by damp. The cavity was created to prevent moisture from entering the interior of a structure and also assists in allowing the build-up of moisture and water to be able to drain out of the wall through using weepholes. These are tiny gaps in the wall’s pointing, which allow water to escape from these spaces, which are usually placed at intervals of 1 meter along the leaf’s exterior.
The walls of solid construction differ in a significant way in that they deal with water in a different way because bricks are porous, it is quite simple for moisture to move from the outside to the interior wall, causing an impermeable damp issue and to address this, walls must be much more robust, which means they are more expensive to construct. They are also less efficient because they do not provide adequate heat or sound insulation due to the existence of an air gap within the cavity.
It is important to know that CWI can cause damp problems, and could contribute to the existing damp issue or accelerate the process of the wall’s failure. It is typically due to the wrong insulation material being employed in the cavity, as the material isn’t letting the wall breathe and evaporate excessive moisture. The material acts as a bridge and transfer the moisture to the wall, creating an issue of damp, but modern, natural materials are now available which allow the wall to breathe better.
Benefits
The walls may allow for some resistance to fire.
They reduce the chance of condensation, moisture build up, and penetrative damp issues.
The cavity wall is a great way to reduce the cost of heating the building. Because the air inside the cavity acts as an insulation.
They provide excellent sound insulation when compared to homes that has a brick wall, which reduces the impact of sound from outside.
Cost-effectively Cavity Walls are cheaper to construct than solid walls because they don’t need to be as thick.
It protects against efflorescence, which is a white marks on the exterior brickwork when water gets inside the wall, leaving crystalline salt deposits.
The wall ties are the sole element that binds the two walls and they are impervious to moisture. Because there is no direct contact between the two sides of the wall, there is very little chance of moisture getting into the wall. The wall was constructed to resist the force of rain entering the wall and transferring to the interior.
Advantages
Cavity Wall construction is more challenging than constructing a solid wall, it requires lots of supervision during the construction phase to ensure that it is completed in a proper manner.
The amount of expertise required is greater for the construction of cavity walls. Therefore, expert architects Highly skilled masons, highly skilled laborers are required.
There is always the chance that moisture could penetrate from the exterior leaf of the wall and reach the interior, since cavities are not designed for filling with material.
If the material that is insulative gets wet, it can cause cold bridging or thermal Bridging. The term thermal bridging refers to the act of heating moving through an object that has more electrical conductivity than the surrounding materials.
The retrofitting of CWI to a wall cavity may create air pockets that are not filled – creating cold spots within the wall, which could attract condensation.
As we mentioned before, wall tie corrosion can also be an issue, and when they are installed using CWI, the leaf’s outer surface is colder, which means it becomes more wet. This means it speeds up the process of corrosion on wall ties. There is no way to replace wall ties in a sufficient way.
If you were planning to install CWI the thickness of it will be limited by the size of the cavity, as they differ from building to building.
Issues with CWI
For some , Cavity Wall Insulation could be extremely beneficial, reducing heating costs and keeping your home warm for longer. However, there are some issues that can arise from the retrofitting of cavity wall insulation, or, if you’ve had it installed previously, you might have already encountered issues. In the majority of homes, the cavity is intended to function as an open space, so filling the space with CWI material could result in the problem of penetrative damp.
In the event of a decrease of air flow around the cavity , it is likely that the moisture is unable to evaporate. If the insulative material gets saturated, it will store moisture close to the internal leaf, and act as a bridge to allow moisture to move across the cavity, which can lead to damp issues that penetrate. In addition, it can lead to water accumulating near to the flooring joists, which can cause flooring rot, and eventually flooring failure.
We’ve also witnessed many instances of cowboy installers who failed to install CWI, and as a result, there is a lot of homeowners who been left with a house that isn’t as efficient because the CWI wasn’t installed correctly and gaps without insulation were created in walls, which has led to cold spots, which can cause condensation spots on the interior wall.
This can cause issues when the structure is wood or steel framed because the cavity is utilized to prevent moisture from the structure’s frame. If the cavity is lined by CWI then moisture is left to sit around and could cause corrosion and rot of the frame, which could lead to structural damage.