What Is Cavity Wall Insulation?
Cavity wall insulation is when a material is used to fill the space in between the two "skins" of a cavity wall.
The material inserted can be, but is not limited to:
- Glass wool
- Rock wool
- Cellulose
- Foam
- Polystyrene beads
Most modern buildings are already built with insulated cavity walls, but older buildings do not. Almost a third of heat lost in uninsulated homes escapes through the walls.
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How Does Cavity Wall Insulation Work?
Small holes are drilled at gaps of about 1 metre in the wall, and the insulation is injected through the holes. The holes are then sealed with cement or white putty.
Installers are normally careful in their placement so as not to destroy the aesthetic of your house, but you can always touch up the filled-in holes with paint to match the surrounding walls.
The main aim of this type of insulation is to reduce heat loss that may occur when the cavity between the skins is empty. Filling the space in a cavity is done to reduce the possibility of convection.
By removing the possibility of air moving around between the two leaves of a wall, convection can be greatly reduced or even eliminated. To what degree depends on the quality of material used. The less air that is able to circulate, the less heat that can be lost.
It is a simple process which will only take around two hours. We do not recommend doing it yourself, due to the potential to cause structural or cosmetic damage to your outer walls.
What Types of Cavity Wall Insulation Are There?
There are two main varieties of cavity wall insulation:
- Pumped insulation
- Solid insulation 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 projects, as there is minimal interference with the fabric of the 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
- Mineral wool polystyrene board cavity wall insulation
Pumped Insulation
For insulating existing cavity walls, a common method is "pumped" insulation. This involves injecting insulation material through small holes drilled in the outer wall.
It is generally preferred for retrofits because it is less invasive, making it a faster, more affordable, and less disruptive option for homeowners.
There are different types of pumped insulation available:
- Bonded bead: This uses small polystyrene beads mixed with a bonding agent that hardens for stability. The beads fill the entire cavity, eliminating cold spots while still allowing moisture to drain.
- Pumped foam: This involves a polyurethane foam that expands significantly as it dries, ensuring complete filling of the cavity and eliminating air gaps. Pressurised polyurethane foam is particularly useful for cavity walls that already have some insulation, as it can fill any remaining spaces or address issues like sagging.
Mineral Wool Polystyrene Board Cavity Wall Insulation
For solid cavity wall insulation, the common materials are usually rolls or batts of mineral wool, or rigid boards of polystyrene. These can offer excellent thermal performance, particularly in new construction.
However, when it comes to insulating an existing house, these methods are less frequently used because they typically require more construction work around the cavity walls.
How Much Does Cavity Wall Insulation Cost?
The cost of cavity wall insulation varies widely depending on several factors, but you can generally expect to pay between €7.50 and €10.50 per square metre.
For an average three-bedroom semi-detached house, the total cost typically ranges from €1,900 to €2,200. The final price is determined by the specific characteristics of your home and the chosen insulation material.
Several key factors will influence the final cost of your cavity wall insulation project:
- Size of your home: The larger the wall area that needs to be insulated, the higher the overall cost will be.
- Width of the cavity: The space between your inner and outer walls can vary. A wider cavity will require more insulating material, increasing the cost.
- Type of insulation material: The material you choose will have a direct impact on the price. For example, certain types of injected foam might be more expensive than bonded beads.
- Accessibility: If a contractor needs to use scaffolding or special equipment to reach a difficult area of your house, it will add to the labour costs.
- Labour costs: These can vary based on the contractor's rates, the complexity of the job, and your geographic location.
| Property | Wall Area (m²) | Cost per m² | Estimated Total Cost |
|---|---|---|---|
| Apartment | 70–100 | €8.50–€10.50 | €600–€1,050 |
| Two-bed semi-detached | 120–150 | €8.50–€10.50 | €1,020–€1,575 |
| Three-bed semi-detached | 180–220 | €8.50–€10.50 | €1,530–€2,310 |
| Four-bed semi-detached | 250–300 | €8.50–€10.50 | €2,125–€3,150 |
The prices above are estimates and do not include any SEAI grants. You should always get multiple quotes from different contractors before making a final decision.
Do I Need Planning Permission for Cavity Wall Insulation?
No. Planning permission is not required for cavity wall insulation. However, if your home is a protected structure or in a conservation area, you should enquire with your local council before commencing with your insulation work.
Are There Grants for Cavity Wall Insulation?
The SEAI is offering grants for cavity wall insulation to all homeowners. The grant amount is dependent on the size of your property but ranges from €700 for apartments to €1,700 for detached homes.
The grant is only available for homes that were built and occupied before 2011. To apply for a wall insulation grant, you can apply online via the SEAI Individual Home Energy Upgrade application portal.
| Property Size | Grant Value |
|---|---|
| Apartment (any) | €700 |
| Mid-terrace house | €800 |
| Semi-detached / end-terrace | €1,200 |
| Detached house | €1,700 |
How Much Money Can Cavity Wall Insulation Save You?
Keep in mind that by installing insulation you should also be able to save up to €300 a year off your heating bills, so view cavity insulation as an investment that will pay off after just a couple of years.
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What Are the Benefits of Cavity Wall Insulation?
There are several benefits to having your wall cavities insulated, from saving on energy costs to improving the value of your property.
- Heating bills: Proper wall insulation can significantly increase energy efficiency and lower your energy bills.
- Environmentally friendly: Reduces the amount of energy you need for your home heating.
- Noise reduction: Lowers the amount of noise you hear from inside your home.
- Heat retention: Makes your home more comfortable, especially during colder months.
- Higher property value: Well insulated walls help increase the BER rating of your home.
- Energy neutrality: Can help as part of a passive house.
- Combine with a heat pump: Together with a heat pump and other energy saving gadgets you can further lower your bills.
How Do I Find a Cavity Wall Insulation Contractor?
In order to find a contractor that both suits your needs and budget for your home cavity wall insulation project, we recommend following these steps:
- Online search: Search for contractors in your area and filter for those who are best reviewed.
- SEAI website: Consult the SEAI website for their list of registered contractors. If you are applying for a grant, you will need to contract a registered contractor from the SEAI.
- Check reviews: Look for contractors who are well reviewed. Look for those with positive reviews regarding quality of work, professionalism, budget, etc.
- Get recommendations: If any family members or neighbours have had insulation done, ask them for a recommendation.
- Contact multiple contractors: In order to get the best price, compare multiple quotes from multiple contractors before making your decision.
Potential Challenges of Cavity Wall Insulation and How to Avoid Them
While cavity wall insulation offers significant benefits, it is important to be aware of potential issues that can arise from poor installation.
- Dampness: Dampness can occur, but this is generally due to poor installation as opposed to a downside of the insulation itself. 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.
- Structural damage: Improper drilling or sealing can cause cosmetic or even structural damage to your outer walls. This is why it is essential to hire a qualified and registered contractor.
Frequently Asked Questions About cavity wall insulation
We do not recommend carrying out the insulation process by yourself. Cavity wall insulation requires specialist equipment and trained personnel to make sure it is done correctly to avoid any long-term issues.
Most houses built after the 1940s in Ireland have cavity walls.
You can check the thickness of your external walls (if they are more than 260mm thick, it is likely a cavity wall) or look at the pattern of the bricks (if they are laid lengthways in a simple alternating pattern, it is likely a cavity wall).
Dampness can occur, but this is generally due to poor installation as opposed to a downside of the insulation itself.
Walls that are in an area of the house that have wind-driven rain should be insulated with bonded bead insulation to allow any water that permeates to trickle down.
Done properly, cavity wall insulation should last the entirety of the lifetime of the building.