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Cavity Wall Insulation, Are All Homes Suitable for Installation?

cavity wall insulation failure removal

What is Cavity Wall Insulation?

Cavity Wall Insulation is the filling of the gap between the internal wall and external wall of your home with insulative material, usually a polystyrene or wool based filling. Houses built in the last 10 years will have been built with insulation, similar to the insulation in your attic, big sheets of fluffy wool-like material. Older houses were built with a solid wall, however, houses built after the 1920s were built with a cavity (an empty space).


Cavity Wall Insulation was originally pushed as a scheme, funded by a ‘green tax’ on household gas and electricity bills, sought to retrofit millions of homes in the UK with insulation. This was meant to cut emissions and reduce charges by making homes more energy efficient.


Millions were persuaded to sign up to the scheme by the promise of cheaper bills from call-centre staff and door-to-door salesmen subcontracted by energy firms obliged to meet Government targets.


The cavity wall insulation suppliers were put under enormous pressure to reach tight targets, meaning that many companies who installed the insulation cut corners to save time and escape government fines. Meaning thousands if not millions of homes across the UK have been affected by botched CWI jobs, luckily with a 25-year guarantee from CIGA.


Not all cavity wall insulations are faulty, but the vast amount that are causing problems are because of product degradation, inappropriate application in homes that are unsuitable for the retrofitting of Cavity Wall Insulation, or just general poor installation techniques from cowboy installers.

Cavity wall Insulation being installed
Cavity Wall Insulation being installed by injection.

Properties that are Unsuitable for Cavity Wall Insulation

There are quite a lot of cases of homes that were retrofitted CWI by cowboy tradesmen that were trying to meet governments targets before deadlines and generally trying to gain financially by installing CWI, even in homes that were absolutely not suitable for the installation in the first place. Meaning a lot of people were promised homes that would be warmer and they’d be paying lower energy bills, but in the end… they were left with damp and rot problems.

Properties Exposed to Wind-driven rain

Properties that are exposed to wind-driven rain, mostly those on the west coast of Britain where strong winds blow in from the Atlantic Ocean. The rainwater is blown onto the surface of the external walls and can penetrate through weak spots like gaps and cracks in the mortar, usually round door and window frames. Once the damp and moisture penetrates the outside surface of the wall it begins to seep into the insulative material in the cavity and then from there into the internal part of the wall. Meaning that a penetrative damp problem will start to arise, with unsightly damp spots appearing on your wall which could then lead to mould.  

Wind driven rain and cavity wall insulation
This diagram from LABC gives a breakdown of the most exposed places to wind-driven rain.

Timber Frame Properties

Timber frame properties require air circulation to prevent the timbers around the property from getting moist and potentially rotting. Most homes are built with suspended timber floors, these properties have air bricks which are strategically placed around the property allowing a good amount of airflow around the walls and the floors of your home. If you live in a full timber framed home you will have more air bricks situated around the walls of your home, this keeps the timbers dry and healthy as there is a gap for the air to circulate allowing it to dry out any moisture, meaning they will stay dry; lasting as long as possible.

If you were then to retrofit these cavities with CWI then you would be increasing the amount of condensation forming and moisture being trapped against the buildings frame as the gap that allows air to move round the building has now been filled. Which in turn could lead to wood rot as well as a damp and mould problems on your walls. There are also cases where cowboy installers have completely filled all the gaps in the airbricks, this should absolutely never be done.

Cavity Wall Insulation Timber frame property
An example of a timber frame property.

Steel Frame Properties

The premise is the same for steel frame properties as timber frame. They are absolutely not suitable for cavity wall insulation, however it is not timber rot that occurs, it is corrosion of the steel instead. A steel frame property that has been retrofitted with CWI can be deemed as structurally unsafe depending on the extent of the corrosion, meaning you may struggle to sell your home, or you may struggle having a mortgage granted on the property – dependant on the risk that the surveyor deems the property is in. As well as this the lack of air circulation is not only damaging structurally but can also be damaging to your health.

Properties With Damaged Brickwork and Mortar

If a property has damaged or faulty brickwork, then it is at risk to a penetrative damp problem. Similar to properties that are exposed to wind-driven rain, the rainwater can penetrate the external wall through the gaps in the damaged wall and find itself penetrating to the cavity. If the cavity is filled with insulative material, then again it can make the material moist and then it can penetrate through to the internal leaf of the wall causing damp spots and potentially mould.

Cavity wall insulation wall with brick and mortar damage
An example of a wall with severe masonry damage.

Properties With Significant Amounts of Rubble and/or Mortar Left In The Cavity

When building homes quite often the cavity becomes filled with excess mortar from the bricklaying process along with rumble like pieces of stone and brick. This can work as an enabler for moisture that penetrates the external wall as it can carry the moisture from this external part of the wall to the internal leaf. There are also wall ties which are used in the wall during construction and span the cavity, from the internal to external parts of the wall and they are used for stability of the building. However can also carry moisture across the cavity leading to penetrative damp when there is debris in the wall cavity.

Damp caused by poor cavity wall insulation
The extent of damp that can be cause by dodgy Cavity Wall Insulation.

Properties with Cavities Less than 50mm

Properties that have a cavity that is less than 50mm are advised not to have any cavity wall insulation fitted as the gap is to small. If you were to fill the cavity with insulative material it would allow for penetrative damp issues, as the idea for building walls with small cavities were to help stop damp issues and prevent the water penetrating the inner skin on the wall. With a cavity wall any water that goes through the external skin of bricks would fall down the cavity and dissipate due to the movement of air around the cavity, keeping the home damp free.

Since the 1980s, Building Regulations have stated that cavity walls are filled with insulation as they are built – in most cases the insulation is fixed to the inner skin of the cavity wall, leaving a gap between the outer, external cavity skin and the insulation. This allows any moisture getting through the first skin, to still get air flow to it meaning it’ll keep dry and penetrative damp will not become a problem on internal walls.

w600 RT2 Application bdef5c
An example of a Wall Ties & how Cavity Wall Insulation is now installed as the walls are built.

Still Unsure Whether You Property Is Suitable for Cavity Wall Insulation?

The best thing to do is to speak to a surveyor and they will tell you, or failing this talk to a trusted and registered cavity wall insulation installer that is backed by CIGA (Cavity Insulation Guarantee Agency) and they will give you honest advice on the best solution for your home.

How can Housing Triage Help You?

If you have had Cavity Wall Insulation installed inappropriately and feel it could be causing damage to your beloved property then Housing Triage are here to help you claim operating on a “No win, no fee” agreement, helping you claim compensation against the removal costs of the cavity wall insulation. A surveyor will provide an estimate of the cost of any works needed to repair the damage to the property and place it back into the condition it was in prior to the cavity wall insulation being installed.

If you’d like to book a free survey get in touch now.

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