Cavity Wall insulation is one of the simplest and most cost-effective ways to insulate a home in order to save money and improve your comfort by making it more energy efficient.

The average home can lose as much as much as 30% of its heat through its external walls, making cavity wall insulation an ideal way to reduce heat loss.

Cavity wall insulation installed also leaves your home visually unchanged, having no affect on its appearance.

Key Takeaways

  • Cavity Wall Insulation is a low-impact and a cost-effective way to insulate the external walls of a house.
  • SEAI grants of up to €1,700 are available to help with the cost of cavity wall insulation.
  • Cavity Wall Insulation can achieve U-Values of as low as 0.18 W/m²K.

What is a cavity wall?

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.

What is cavity wall insulation?

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.

Types of Cavity Wall Insulation

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
  • Bonded Bead Cavity Wall Insulation
  • Pumped Foam Cavity Wall Insulation
  • KOREFILL Cavity Wall Insulation
  • Mineral Wool & Polystyrene Board Cavity Wall Insulation

Pumped Cavity Wall Insulation

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

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 Cavity Wall Insulation

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.

KOREFILL Cavity Wall Insulation

  • High performance expanded polystyrene bead cavity wall insulation
  • Available in KOREFILL Original and KOREFILL Diamond for different thermal performance.
  • Thermal Conductivity of 0.35 W/mK (KOREFILL Original) and 0.33 W/mK (KOREFILL Diamond).
  • Can achieve U-values of 0.18 W/m²K (170mm KORE Fill Diamond) or 0.15 W/m²K (200mm KORE Fill Diamond).
  • Suitable for full fill or partial fill walls with a remaining wall cavity of 40mm or greater, and walls up to 12m in height.

Mineral Wool & Polystyrene Board Cavity Wall Insulation

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.

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.

Cavity Wall insulation can significantly reduce the heating bill for a 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 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.


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.

Not all houses are suitable for being retrofitted with cavity wall insulation. First, the wall cavity needs to be at least 50mm in width at minimum. Though it would be ideal if it were more than that.

If a house was built after the 1940s in Ireland it most likely has cavity walls. If you still aren’t sure, measure the thickness of the outer wall of your house. If it is more than 260mm thick, it is likely a cavity wall.

Potential damp problems from Cavity Wall Insulation tend only to arise from bad installation or poor understanding of your property.

If a house has a brick wall in an area with wind driven rain there is a possibility of moisture permeating through solid insulation. Bonded bead insulation solves this by allowing water to trickle down through the honeycomb.

Properly installed cavity wall insulation should help to prevent damp in most environments.

Choosing the best cavity wall insulation will depend on a number of factors such as your local environment, the thermal performance you wish to achieve, and whether it is a new build house or retrofit project.

Insulation FAQ

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