Cavity Wall Insulation

A Cavity Wall, as opposed to solid walls, are external walls of a building which have an empty cavity space between the inner and outer walls. The purpose of this wall cavity is to allow for water to drain from the base of the wall. It also creates a slow-moving air gap between the walls to reduce heat loss.

The inner and outer wall are known as the leaves of the cavity wall, with wall ties connecting the inner and outer wall in order to provide structural integrity. The majority of houses built in Ireland after the 1940s have been built with cavity walls.

Cavity Wall Insulation refers to any insulation material which is installed in the space between the inner and outer walls of a cavity walls to reduce further the amount of heat lost through the walls by trapping air from circulating.

It can also have other benefits such as preventing dampness, improving the structural integrity of the wall, and providing sound insulation so that less noise gets in from outside.

The effectiveness of cavity wall insulation is measured by its U-value, which tells how much heat will pass through the insulation. The lower the U-value of your insulation, which is measured in W/m²K, the better its performance will be.

There are two main varieties of Cavity Wall Insulation: Pumped Insulation and Solid |nsulation Boards or Rolls. The type of insulation material best suited to your house will depend on whether it is a new build or retrofit project. Pumped insulation is typically more suited to retrofit project, as there is minimal interference with the fabric of cavity wall.

The main varieties of insulation materials used on cavity walls are:

Pumped Cavity Wall Insulation is where insulation is pumped into cavity walls through small holes drilled into the outside of the external wall. Pumped Cavity Wall Insulation is typically the best option for retrofit works, as it can be done with minimal interference with the fabric of the building. This makes it cheaper, quicker, and less disruptive to the homeowner.

Bonded Bead cavity wall insulation consists of small beads of polystyrene mixed with a bonding agent which hardens as it dries, ensuring structural stability.

The beads fill the entirety of the space in cavity walls, ensuring there are no cold spots, and still allow moisture to trickle down and out the bottom.

Pumped Foam Insulation is a polyurethane foam which can expand to up to 200 times its original size as it dries. This ensures that it fills the entirety of the space in cavity walls, leaving no air gaps. 

Pressurised polyurethane foam insulation is ideal for cavity walls which may already have some wall insulation installed. It can fill the remainder of the space and correct any air gaps or sagging which has arisen.

Solid cavity wall insulation typically consists of rolls or batts of mineral wool or else solid boards of polystyrene insulation. Solid cavity insulation can provide a storing thermal performance in new build homes. However, they are less common when retrofitting a house as it requires more construction work in and around the cavity walls.

The cost of having cavity wall insulation installed will vary from project to project based on multiple factors related to the property, materials, and installation work.

When looking at the cost of insulation the main factors to keep in mind are:

The larger amount of surface area your home has, the larger the cost of the project will be. This is also true of how wide the cavity gap in your home is, something which will need to be assessed and measured before work can begin.

Of the two main types of insulation used in these projects, Polyurethane Spray Foam insulation typically costs more per m² than Polystyrene Bonded Bead insulation.

Some rough cost estimates for cavity wall insulation in Ireland would be:

Detached properties will need to be surveyed in order to give an accurate assessment. These are only rough estimates, and a proper pricing will vary based on the factors mentioned above. 

For new builds, other options such as Polystyrene Boards and Mineral Wool might seem cheaper upfront. However, they will likely not have the same thermal performance at the same thickness.

1. An Assessment will be carried out on-site to measure the available space in the cavity walls and check for any existing problems with dampness.
2. Holes are drilled in the cavity wall from the outside in a pattern which ensures that all areas of the wall will be filled, without any blank spots which would undermine the performance of the insulation.
3. The insulation is injected into the cavity walls at high pressure using compressed air until all areas of the wall have been filled.
4. The holes are then filled in with mortar and matched with the existing surface of the cavity walls to reduce the visual effect.

Note: If you live in an apartment, terraced house, or semi-detached house steps will also be taken to ensure no work encroaches on neighbouring properties.

One advantage of Cavity Wall Insulation is that almost all the work is carried out on the outside of the property. This means that there will be minimal disruption to the homeowner while the work is being carried out.