Types of Cavity Wall Insulation

Cavity wall insulation is used to reduce heat loss through a cavity wall by filling the air space ( the cavity) with material that reduces the transfer of heat.

The installation of cavity wall insulation (CWI) was promoted as an affordable and effective method of reducing heating costs and reducing the UK’s greenhouse gas emissions.

Cavity wall insulation is a great product if installed correctly and in a property that is suitable for CWI.

Three Main Types of Cavity Wall Insulation

Whilst there are numerous types of insulation material, we will look at the the three most widely used in UK homes.

Polystyrene Bead Wall Insulation

polystyrene beads cavity wall insulation

Expanded polystyrene beads , when combined with an adhesive to keep them in place and bonded together, is a very common method of insulation. These are pumped into the wall cavity, mixed with an adhesive which bonds the beads together to prevent them spilling out of the wall.
Particular caution should be taken when using this type of insulation, particularly with stone walled houses or properties which are particularly exposed to driving rain.

Foam Wall Insulation

Expanding foam insulation is used as a cavity wall insulation particularly in properties that either have stone walls or uneven walls and cavities. It has advantages in terms of the size of holes required to be drilled into the walls and its ease of flowing to fill the gap.damp foam cavity wall insulation

Foam wall insulation is not the ideal choice for most properties as it can dramatically damage the airflow through a property and moisture can quickly collect and become trapped.

Some types of foam insulation are now known to decay over time, producing toxic fumes and encouraging damp penetration.

Mineral Wool Insulation

Mineral wool insulation such as Rockwool is by far, the most commonly used type of insulation for domestic properties in the UK. It is produced by heating and spinning rock, to create a fibrous material. This is blown into the wall cavity, until it has filled the gap between the inner and outer walls, completely.blown mineral wool cavity wall insulation

Mineral wool does not absorb water and does not generally allow any rain water to get from through the outer wall to reach the inner. A minimum cavity width of 50mm is required for this material to be installed. If incorrectly installed or installed in the wrong sort of property, damp will still occur.

Mineral wool is prone to settling over time, leaving gaps and creating bridges for damp to travel from the outer wall to the inner.

Why Does Cavity Wall Insulation Fail?

Cavity wall insulation can stop being fit for purpose for a number of reasons. The most common factors that we encounter fall into 4 main groups;

The property wasn’t suitable for CWI installation.

CWI has degraded prematurely and is actually damaging the thermal qualities of the house.

 Insulation was not installed correctly,or the wrong material was used.

The CWI was damaged due to external factors such as flooding, leaks or fire.

As we are already aware, once damp has entered your property, the acute and chronic effects on health can be catastrophic if not dealt with as soon as possible.

Unsuitable Property

There have been many instances where cavity wall insulation has been fitted into houses which were considered unsuitable for this type of alteration.

Typically steel or timber framed buildings or those manufactured from precast concrete.

Additionally,  if a house has poor or damaged  brickwork and mortar, or if it is exposed to driving rain, then this would also make the property unsuitable for the installation of CWI.

Premature Degradation

When cavity wall insulation was in its infancy, the material predominately  used was  typically foam. Over a period of years this will degrade. This is likely to become harmful to health due to a combination of gasses released from the foam and the ensuing damp.

Incorrectly Installed CWI

This is probably the main cause of failing CWI.

Often due to insufficient quantities of the relevant product being used which creates voids where moisture could be held.

Sometimes air vents and ventilation ducts become blocked as a result of not following the manufacturer’s installation guidance.

Fire/Flood damage

This is pretty much self-explanatory. Insulation can either become water logged or can melt in the heat.

Further information regarding the types of cavity was insulation and their potential to fail can be found by using the following link AskJeff