A Cavity Wall is a type of wall construction in which there is an open space or cavity that is left between two layers of brickwork, it’s also referred to as an Hollow Wall. The gap between the two layers of brickwork known as the inner leaf and outer leaf. In modern constructions , the gap is filled in Cavity Wall Insulation (CWI) an insulative material. It is applied in the course of construction, not injecting it like when it is retrofitted. The construction of buildings with cavities walls first came into use during the 19th century and was adopted widely in the 1920s.
Initially , they were built with no insulation. They were slightly smallerthan the typical sizes of cavities are typically between 4 and 10 centimeters. However, there are numerous instances of home owners having CWI retrofitted. From the 1970s insulation in the cavity became standard in the late 1990s, building regulations mandated it for new buildings.
In a Cavity Wall, the two brick skins are held together with what is commonly referred to as a Wall Tie which are usually constructed from metal. The wall was constructed using ties made from iron, mild steel or copper, but these materials were susceptible to corrosion and wall tie corrosion first came to light in the 1960s. Moving forward from this they began to use stainless steel since it’s less susceptible to corrosion. which keeps the structural integrity for longer.
The walls were first designed and built to prevent problems caused by damp. The cavity was created to stop water from getting into the interior of a structure and assists the accumulation of moisture and water to drain back out of walls through the use of weepholes. These are tiny gaps in the wall’s external pointing that permit water to escape from that are generally placed at intervals of 1 meter along the leaf’s exterior.
Solid walls differ significantly in that they deal with moisture in a very different way because bricks are porous. It is simple for moisture to travel from the outside to the inside of the wall, creating an impermeable damp issue and to address this, the walls have to be more solid, which means they will cost more to construct. They also have lower efficiency as they don’t provide the necessary heat or sound insulation because there is not the existence of an air gap inside the cavity.
It is important to know that CWI can create damp problems, and can increase the severity of an existing damp problem , or increase the likelihood of the wall’s failure. This is usually due to the wrong type of insulative material installed in the cavity because the material isn’t letting the wall breathe, allowing it to dry out excess moisture. The material acts as a bridge and transfer the moisture to the internal wall creating a damp problem, however more modern and natural materials are now available which allow the wall to breathe better.
Benefits
The walls may allow for some protection against fire.
They will reduce the possibility of condensation and moisture build up, and penetrative damp issues.
The cavity wall could reduce the heating costs of an entire building. As the air in the cavity works as an insulator.
They are a good sound-proofing option in comparison to houses that has a brick wall, and reduce the impact of outside sound.
The economics of Cavity Walls are cheaper to construct than walls of solid construction because they don’t need to be as thick.
It provides protection from efflorescence. They are white marks on the exterior brickwork, which form the wall when water has entered the wall, leaving crystal salt deposits.
The wall ties are the sole element that binds both walls and are impervious materials. Since there is no direct contact between the two leaves of the wall there is hardly any possibility of moisture getting to the internal wall. The wall was designed to resist the force of rain infiltrating the wall and transferring towards the interior.
Disadvantages
Cavity Wall construction is more difficult than solid wall, it requires a lot of supervision during its construction phase to ensure it is done properly.
The level of skill required is higher when building cavity walls. Expert designers, highly skilled masons and labourers are needed.
There is always the possibility that moisture can penetrate from the external leaf of the wall and reach the internal, as cavities are not designed to contain material.
If the material that is insulative gets wet, it can result in cold bridging, or thermal Bridging. This is the term used to describe the phenomenon that involves heat moving across an object that will be more conducive than the objects around it.
Retrofitting CWI to a wall cavity could create air pockets that are not filled – which can cause cold spots on the interior of the wall which will attract condensation.
As we mentioned before, wall tie corrosion is also an issue. When wall ties are fitted using CWI the outer leaf gets colder which means it gets wetter. It can also speed up the corrosion process of the wall ties, and there isn’t any way to replace wall ties in a sufficient way.
If you are planning to install CWI the thickness of it will be limited by the size of the cavity as they will vary building to building.
Get in touch with northwestwallties.co.uk when searching for wall tie specialists.
CWI issues CWI
For some , Cavity Wall Insulation could prove extremely beneficial. It will reduce heating costs and also keeping your home warmer for longer. There are however issues to be aware of when retrofitting insulation to a cavity wall or, if you’ve had it previously installed, you could already be experiencing issues. In most houses, the cavity is intended to function as one, and filling that gap with CWI material could result in a penetrative damp problem.
If there is a reduction in airflow around the cavity meaning it is difficult for moisture to evaporate. Additionally, if the insulation material gets saturated, it will store moisture near to the internal leaf, acting as a bridge for moisture to pass through the cavity, which can lead to damp issues that penetrate. It is not just this, but it could cause moisture being sat near the flooring joists and causing floor rot and ultimately flooring failure.
We’ve also witnessed several instances of cowboy installers who have installed CWI in a hurry, which is why there are a large number of people who’ve found themselves with a home that is less efficient as the CWI isn’t fitted properly and the gaps without insulation have been placed in the walls, resultant in cold spots that later cause condensation spots on the internal wall.
It could also create problems in the event that the building is made of timber or steel, since the cavity is designed to block moisture from the frame of the building. If the cavity ends up packed with CWI then moisture will be permitted to remain close to the frame and can cause corrosion and rot of the frame which can lead to structural damage.
