Insulating your home is one of the most effective ways to make it more energy efficient, reducing your energy bills and making it more environmentally friendly.

The average home can lose as much as much as 30% of its heat through its external walls, making cavity Wall Insulation one of the most cost-effective ways to improve your home.

Having modern insulation put in can lead to significant savings on your heating bills, improve the comfort of your home, and make it more environmentally friendly.

What is a Cavity Wall

Most buildings in Ireland made after the 1940s have a hollow space between the inner and outer masonry walls. This is known as the cavity of the wall. 

The purpose of this 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.

What is Cavity Wall Insulation

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

This will greatly improve the comfort of your home, and reduce the amount that you will need to spend heating it.

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.

Types of Cavity Wall Insulation

There are three types of insulation which can be used in cavity walls, though only two of them are practically applicable for renovations of existing homes. 

The main types of insulation which can potentially be used in cavity walls are:

  • Bonded Bead Insulation (Retrofit)
  • Spray Foam Insulation (Retrofit)
  • Polystyrene Boards (New Build)
  • Mineral Wool (New Build)

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

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.

Spray Foam Insulation

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

Polystyrene Boards & Mineral Wool

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.

How Much Does Cavity Wall Insulation Cost

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:

  • Property Size
  • Cavity Width
  • Materials Used
  • Accessibility
  • Labour

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:

  • Two-Bed Semi-Detached House: €1,500 – €1,900
  • Three-Bed Semi-Detached House: €1,900 – €2,200
  • Four-Bed Semi-Detached House: €2,200 – €2,600

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.

Cavity Wall Insulation Grants

The SEAI offers grant funding for almost all homeowners to help with the cost of having cavity wall insulation installed in their houses or apartments.

The grant is available to all homeowners, including private landlords, so long as the property was built and occupied before 2011.

Insulation Type Grant Value
Cavity Wall Insulation Apartment (Any) – €700
Mid-Terrace House – €800
Semi-Detached/End-Terrace – €1,200
Detached House – €1,700
Home Insulation Grants

Cavity Wall Insulation Benefits

Having cavity wall insulation on your home can create big improvements in your quality of life, as well as financial gains from the improvements to the property.

With up to 30% of your home’s heat lost through the external walls, improving their insulation can result in massive savings on your electricity, oil, or gas bill when it comes to heating your home.

Properly insulating your home will drastically reduce the amount of electricity or oil used in home heating, making your property much friendlier for the environment.

Having a layer of insulation installed in the walls of your home can drastically reduce the amount of noise which filters through from the outside.

Insulated walls which are better at retaining heat will provide a more comfortable experience at home.

Cavity Wall Insulation can also improve the structural integrity of your wall by preventing any damage from damp.

Any insulation upgrades to your home will help to improve its BER and add value to the property if it is sold later.

Cavity Wall Insulation Installation

  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.


No, planning permission is generally not required to have cavity wall insulation installed in your home. However, you should consult on this if it is a protected structure or in a conservation area.

The most common types of cavity wall insulation, bonded bead and spray foam insulation, should last for the lifetime of the building.

Cavity Wall Insulation requires specialist equipment and knowledge to inject the insulation into your wall and ensure that it is done thoroughly and professionally. This should not be done as a DIY project for someone who is not trained.

Insulation FAQ

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