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

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

Bonded Bead and Spray Foam are the most popular insulation materials for cavity walls due to their high performance and the fact that they can be pumped into the cavity between walls from outside, with little disruption to the building.

Bonded Bead Insulation consists of small beads of insulation, as opposed to the large rigid boards it normally comes in. These are with a liquid bonding agent, which hardens as it dries.

The small nature of the individual beads allows them to fill the entirety of an inaccessible space, and fill it with a solid mass once the adhesive sets. 

Bonded Bead Insulation is beneficial for its ability to fill up irregular spaces, ensuring there are no cold spots in the walls.

Most bonded bead cavity wall insulation will have a U-value of approximately 25-20W/m²K in line with or surpassing building regulations.

Polyurethane is a sprayable foam that is excellent for insulating areas with lots of small spaces or otherwise in hard-to-reach areas such as attics or cavity walls.

Easily usable in retrofitting houses with no insulation, polyurethane insulation expands to up to 200 its original volume as it hardens, ensuring that there are no gaps in the airtight seal.

The breathable seal provided by the spray foam insulation also protects from rain and dampness. Spray foam insulation is more expensive than polystyrene beads, but can achieve a U-value as low as 20W/m²K

New build homes might also have rigid polystyrene boards or rolls of mineral wool insulation laid in the cavity between the inner and outer walls, but this is typically restricted to new builds where it can be put in as the walls are going up. 

The access needed to instal rigid insulation boards on an existing home would require significant construction work dismantling and rebuilding the walls, making it an impractical choice.

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 cavity of your home 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 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 wall 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.