A Cavity Wall is a type of wall construction in which there is an unfilled gap or a cavity that has been left between two layers of brickwork, it’s also known as the Hollow Wall. The gap between two layers of brickwork is known as the inner leaf and outer leaf. In modern buildings, the gap is filled using Cavity Wall Insulation (CWI), insulative material. This is done in construction rather than it being injected like when it is retrofitted. The construction of buildings that have cavity walls were first introduced around the turn of the century and became widespread during the 1920s.
Initially , they were built with no insulation. They were slightly smaller, their size is typically between 4 and 10 cm. However, there are many instances of home owners having CWI retrofitted. Since the 1970s, insulation in the cavity was standard, and during the 1990s, building regulations mandated it for new construction.
Within Cavity Walls, or Cavity Wall, the two skins of brick are joined with what is known as Wall Tie. Wall Tie which are usually constructed of metal. They used to construct with tie-ups made of mild steel, iron or copper, but these materials were prone to corrosion. Wall tie corrosion first became apparent during the 1960s. From there, they switched to stainless steel due to it being less susceptible to corrosion and this keeps the structural integrity intact for longer.
The walls were initially constructed and constructed to avoid problems with damp. The cavity serves to prevent moisture from entering the inside of a building and assists the accumulation of moisture and water be able to drain out of walls through making use of weepholes. These are tiny gaps in the wall’s external pointing, which allow water to exit from these spaces, which are usually placed every one meter on the exterior leaf.
Walls made of concrete differ greatly, as they handle water in a different way due to bricks being porous, it is quite simple for moisture to travel between the exterior and the inside of the wall, creating an issue of damp penetrating the wall, so to combat this walls must be thicker, meaning they cost more to build. They also perform less efficiently as they aren’t able to provide adequate heat or sound insulation since there isn’t the presence of an air gap inside the cavity.
It is important to know that CWI could cause a damp problem, can increase the severity of an existing damp issue, or make it easier for the wall’s failure. This usually happens due to an inefficient insulative material being used to fill the cavity since it isn’t letting the wall breathe and evaporate excess moisture. It acts as a ‘bridge’ and transfer the moisture to the interior wall, causing an issue with damp. However, newer natural material can be used which allow the wall to breathe more.
Benefits
The walls can allow some resistance to fire.
They will reduce the possibility of moisture, condensation build up and penetrative damp problems.
The cavity wall is a great way to reduce the heating cost of a building. As the air in the cavity functions as an insulation.
They can provide good sound insulation when compared to homes with a solid brick wall, which reduces the impact of external sound.
Economically Cavity Walls are cheaper to build than walls that are solid as they don’t require as thick.
It shields against the effects of efflorescence. These are white marks on the exterior brickwork when water enters the wall leaving crystalline salt deposits.
The wall ties are all the thing that connect both walls and are impervious materials. Because there is no direct contact between two of the leaves of the wall, there’s virtually no chance of water getting into the wall. The wall was built to stop rain entering the wall and spreading to the internal.
Negatives
Cavity Wall construction is more complicated than building a solid wall. it requires lots of supervision during the construction phase to ensure it is executed correctly.
The amount of expertise required is higher for building cavities, which is why expert architects Highly skilled masons, highly skilled labourers are required.
There is always the possibility that moisture could penetrate from the external leaf of the wall, and then reach the interior of the wall, as the cavities are not designed to be filled with material.
If the material that is insulative gets wet, it can result in cold bridging, or thermal bridging. The term thermal bridging refers to the act of heat flowing across an object which is more conductive than surrounding materials.
The retrofitting of CWI into a cavity could cause air pockets to not be filled with air – causing ‘cold spots’ within the wall, which can attract condensation.
As was mentioned previously, wall tie corrosion is a problem, when installed with CWI , the outside leaf is colder, which means it gets less moist. This means it speeds up the process of corroding wall ties. There isn’t any way to replace wall ties to a satisfactory level.
If you wanted to install CWI The thickness of it will be limited by the width of the cavity since they will vary building to building.
Issues with CWI
For some people Cavity Wall Insulation can be extremely beneficial, reducing heating costs and also keeping your home warmer for longer. The issue is that it can be caused by retrofitting cavity wall insulation or if you have had it previously installed, you could have already encountered issues. In most properties the cavity is intended to function as one, and filling that space with CWI material could cause the development of a penetrative damp issue.
If there is a reduction of air moving around the cavity meaning it is difficult for moisture to evaporate. If the insulative material gets saturated, it will store moisture close to the inner leaf, and act as a bridge to allow moisture to flow across the cavity, which can lead to damp issues with penetrative penetration. Not only this but it could result in moisture being sat near the flooring joists, leading to floor rot and ultimately flooring failure.
We’ve also witnessed several instances of cowboy installers who bodged jobs installing CWI, and due to this, there are a large number of homeowners who had a home which isn’t as efficient as the CWI hasn’t been fitted properly , and gaps that have no insulation were placed in the walls, leading to cold spots that result in condensation spots appearing on the internal wall.
It can also cause problems in the event that the building is steel or timber framed, because the cavity is used to prevent moisture from the frame of the building. If the cavity ends up filled using CWI then moisture is allowed to remain nearby and could cause an increase in rot and the corrosion of the frame that could lead to structural failure.
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