According to the UK Department for Energy Security & Net Zero, 75% of UK homes have cavity walls. Out of those buildings, 29% of properties lack cavity wall insulation. To make these homes energy efficient and reduce heat loss, you need to choose an efficient type of insulation. The insulation type determines the energy efficiency, insulation costs, longevity, and energy bills.
Cavity insulation material you choose should have high r value, work as a moisture barrier, and insulate your walls properly. This guide will discuss every insulation material suitable to improve thermal resistance and energy saving of your home. So, let’s begin the journey towards selecting the best insulator for your cavity wall insulation.
7 Best Types of Cavity Wall Insulation
An efficient insulation material is that which lowers the heating bills, prevents heat loss through walls, and makes your home warmer. However, if that insulation material is affordable too with higher r values, that’s a plus.
We have compiled some of the efficient materials to insulate cavity walls of your home. Whether you are upgrading the existing insulation or insulating the new builds, these can be the best wall insulation materials.
1. Polyisocyanurate (PIR) Insulation Boards
Let’s talk about PIR boards – my go-to choice when clients want top-notch cavity wall insulation. After working with these boards for over 15 years, I’ve seen firsthand how they’ve changed the home insulation game.
Just last month, I helped my neighbor tackle his heating bill problem. He couldn’t believe the difference in his home’s warmth after we installed PIR in his walls.
Sure, they’re pricier than some alternatives, but here’s the thing – you’re looking at an r value between 6.0 and 7.2 per inch. That’s seriously impressive.
The boards create this amazing moisture barrier that keeps the cavity dry as a bone. I remember this Victorian house I worked on last winter; the owners had struggled with damp for years. Six months after installing PIR, their walls were bone dry and their energy bills had dropped by almost £300.
- These boards laugh in the face of moisture – I’ve never seen a callback for damp issues
- They’re perfect for those tricky cavity spaces that need serious insulation
- Most installations I’ve done are still going strong after 20+ years
- Works like a charm in both old homes and new builds
2. Phenolic Foam Insulation Boards
Now here’s something interesting – phenolic foam boards. Think of them as the ninja warriors of cavity wall insulation. They’re thin but mighty, with an r value of 7.5 per inch.
I remember scratching my head when I first used them back in 2010. How could something so slim work so well? But boy, I was impressed.
Last summer, I installed these in a townhouse with particularly walls with narrow cavities. The homeowner had been told she couldn’t get decent insulation because of the space constraints.
You should’ve seen her face when her first winter heating bill came in – nearly half what she used to pay. The best part? They create this fantastic barrier that keeps heat right where you want it – inside your home.
- Perfect for those annoying narrow cavities that give other materials trouble
- They’re like a shield against fire – I’ve seen the test results myself
- Most of my installations from a decade ago are still performing beautifully
- Great for hitting those tough energy efficiency targets without losing space
3. Closed Cell Spray Foam
Let’s talk about one of the most versatile options for cavity wall insulation. Spray foam has really changed the game in recent years. With an r value between 6.0 and 7.0 per inch, it’s among the most efficient insulation materials I’ve worked with. The beauty lies in how it expands to fill every nook and cranny in your wall insulation.
Most homeowners I’ve helped with insulation projects love how spray foam creates an airtight seal with materials like perlite. It’s particularly good at tackling those tricky spots where heat tends to escape. Sure, the insulation costs might make you think twice, but the energy saving potential usually wins people over.
- Creates an unmatched air and moisture barrier
- Fills irregular cavity spaces completely
- Reduces heating bills significantly
- Lasts decades with minimal maintenance
4. Mineral Wool (Rock Wool)
Here’s an old reliable that’s stood the test of time. Mineral wool, or rock wool as some folks call it, strikes a nice balance between cost and performance. With an r value around 3.0-3.7 per inch, it might not top the charts, but it gets the job done reliably. I’ve seen countless cavity walls insulated with mineral wool still performing beautifully after decades.
What really sets it apart is how it handles sound and fire. Many of my clients choose it specifically because it helps dampen outside noise while providing excellent fire resistance. It’s also one of the more affordable options for cavity wall insulation, making it popular for larger homes.
- Naturally fire-resistant material
- Great for soundproofing as well as insulating
- Made from sustainable materials
- Perfect for budget-conscious projects
5. Polystyrene Beads (EPS/XPS)
These little beads pack quite a punch when it comes to insulating cavity walls. With an r value of 4.0-4.5 per inch, they provide solid thermal resistance while being incredibly easy to install. I’ve found them particularly useful in older homes where other types of insulation might be trickier to install.
The beads flow easily into irregular cavity spaces, creating an even layer of insulation. Most homeowners appreciate how they don’t settle over time like older materials used to. They’re also surprisingly good at handling moisture, which helps prevent damp issues down the line.
- Ideal for irregular cavity spaces
- Maintains performance over decades
- Excellent value for money
- Perfect for retrofitting existing homes
6. Polyurethane Spray Foam
When we look at premium options for cavity wall insulation, polyurethane foam often stands out. Having worked with it extensively, I can tell you its r value of 5.5-6.5 per inch makes it one of the most efficient insulation materials around.
What’s really interesting is how it performs as both an insulator and a moisture barrier. Furthermore, the Polyurethane spray can form the shape more quickly than Polystyrene beads.
Most homeowners I talk to are initially concerned about the higher insulation costs, but the energy saving potential usually wins them over.
From what I’ve seen in practice, homes with polyurethane foam in their cavity walls tend to maintain more stable temperatures year-round. It’s particularly good for challenging installations where you need something that can adapt to irregular spaces or need infiltration.
- Creates an excellent vapor and moisture barrier
- Perfect for complex cavity structures
- Typically reduces energy bills by 40-45%
- Maintains effectiveness for over 30 years
7. Cellulose
Here’s an interesting choice that’s gaining popularity, especially among environmentally conscious homeowners. Cellulose might sound simple – it’s essentially recycled paper treated with fire retardants – but don’t let that fool you.
With an r value between 3.2-3.7 per inch, it holds its own against more synthetic options for cavity wall insulation.
What I find fascinating about cellulose is how it manages to be both eco-friendly and highly effective at keeping homes warmer.
The installation process is straightforward, and its batts fills the cavity beautifully. I’ve noticed more clients choosing it not just for its green credentials but also because it offers solid thermal resistance at a reasonable price point.
- Made from up to 85% recycled materials
- Natural resistance to pests and mold
- Excellent sound dampening properties
- Cost-effective long-term solution
Material | R-Value/inch | Lifespan (years) | Cost/m² (£) | Installation Complexity |
PIR Boards | 6.0-7.2 | 50+ | £25-£35 | Medium |
Phenolic | 7.5 | 20-25 | £30-£40 | Medium |
Spray Foam | 6.0-7.0 | 25+ | £35-£45 | High |
Mineral Wool | 3.0-3.7 | 25+ | £15-£25 | Low |
Polystyrene | 4.0-4.5 | 30+ | £20-£30 | Low |
Polyurethane | 5.5-6.5 | 30+ | £30-£40 | High |
Cellulose | 3.2-3.7 | 20-30 | £15-£25 | Medium |
Each of these materials has its place in modern cavity wall insulation. The choice often comes down to specific factors like cavity width, local climate, budget constraints, and installation preferences.
What matters most is matching the right material to your specific needs while considering both immediate costs and long-term energy savings.
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Schemes For Cavity Wall Insulation Replacement in the UK
There are several wall insulation schemes available for both cavity and solid walls. If your home has solid walls, you will need both external wall insulation and internal wall insulation installation. For these installations, you can choose from various cavity wall insulation options discussed in this guide.
Here are a few of the schemes which offer insulation grants for homeowners and tenants.
All of these schemes provide complete funding for your home insulation upgrades. You just need to find the best insulation installers to fill the wall cavity with insulation materials.
To apply through the ECO4 scheme, you can contact ECO4 installers like ECO Energy Services. We take care of the entire application and installation process for you, without spending a penny.
Final Thoughts
The decision of choosing the insulation material is crucial to avoid the risk of damp and slag formation and moisture damage.
Where insulation stops escaping heat through the walls, it also helps reduce the carbon footprint. In 2025, cavity wall insulation greatly help reduce energy costs and heat loss for households.
However, the performance and wall insulation costs depend on your insulation material selection, so choose wisely.
If you are interested in Polystyrene, Polyurethane, or Polyisocyanurate, rigid insulation should be your preferred choice. Rigid insulation has one of the highest r values, which means it stops more heat transfer through the walls and saves you money.
FAQs
A well-insulated home is often energy-efficient and more comfortable. Plus, the deteriorated and damaged insulation can cause dampness, leading to health issues. If you are the one who likes to save on energy costs, likes comfortable space, and is concerned about your family’s health, replacing the old cavity wall insulation is totally worth it.
It totally depends on the material used and the quality of the insulation. Different materials have different lifespans, which depend on qualities like water and thermal resistance. Typically, you might need to replace the cavity wall insulation between the range of 20 to 100 years.
The primary function of cavity insulation is to improve thermal resistance and reduce heat loss. However, if the insulation is not installed properly or the materials are not moisture-resistant. It might cause dampness down the line. You should keep your insulation in check to avoid deterioration and dampness issues.