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Best Cavity Wall Insulation Option for Excellent Home Energy Efficiency

Cavity wall insulation

Are you considering cavity wall insulation and wondering which is the best option for your home? If the answer is yes, then you’re reading the right guide.

Installing cavity wall insulation isn’t a decision you should take lightly. It’s a significant investment into your home’s energy efficiency, comfort, and overall value and can have long-term implications for your energy bills.  

Here we’ll share details about the best cavity wall insulation options, their advantages, disadvantages and more.


What Is Cavity Wall Insulation?

Cavity wall insulation is a form of insulation that primarily targets the gaps or “cavities” between the inner and outer layers (leafs) of exterior walls. 

If you have a modern home, there’s a huge chance that your wall cavities are already filled, but this can sometimes fail. For older properties, usually pre-1920s, they don’t have wall cavities and therefore there isn’t a space to fill, so internal or external wall insulation is the more appropriate option.

The purpose of wall cavities is to prevent rainwater and moisture from gathering and penetrating the inner walls, causing dampness inside the building. But these wall cavities, when not filled, can cause significant heat loss and even allow excessive outside noise into a home.

As a solution, the wall cavities can be filled with insulating materials to minimise air movement and improve the thermal efficiency of the building. Cavity wall insulation doesn’t affect a building’s appearance at all as the insulating materials are simply injected inside the cavity and sealed in, creating a hidden barrier. Any holes made in the walls to access the cavities are simply filled in.

Best Cavity Wall Insulation Types

It wouldn’t be correct to tell you to pick one type of cavity wall insulation over another, as there’s no one-size-fits-all answer here. That’s why you need to take a look at this quick outline of the best cavity wall insulation types available first:


1. Polyurethane Foam (Spray Foam)

To start our cavity wall insulation list, we’ll go with one of the most popular options, Polyurethane (PUR) foam, also known as spray foam. This insulating material is increasingly the go-to option for homes seeking a highly effective insulation solution. It’s made from organic, carbon-based units that form a stable polymer. 

Essentially, it’s a plastic material you can easily spray to fill up hard to reach nooks and crannies, creating an effective air barrier that blocks out the elements. The spray foam expands to insulate the area, offering unmatched energy efficiency. 

However, how you apply this foam can be tricky, and that’s why it’s best to use a professional installer. Although not the cheapest insulation option on the market, Polyurethane foam is an effective barrier suitable for a range of situations.


  • Fits seamlessly into irregular spaces.
  • Cost-effective when compared to other methods.
  • It’s mould-resistant as it’s an inert polymer.


  • Over time, the spray foam can shrink.
  • Changes in the foam can sometimes lead to water damage risks.


2. Mineral Wool (Rockwool or Glasswool)

Mineral wool, such as rock or glass wool, is another material used for cavity wall insulation that gained popularity in the 1950s. Rockwool is usually created from molten volcanic rock, known for its fire resistance and high-temperature stability while glasswool is mainly made from molten glass and offers excellent thermal insulation at a budget-friendly price. 

What makes this choice an even more popular option now than it was before is that it’s typically made with natural and recycled materials. It’s considered one of the best environmentally-conscious choices that allows you to lower your carbon footprint.

Finally, while there are many claims that mineral wool is water-resistant due to its nature, there are contradicting statements. Various professionals notice that mineral wool can absorb some moisture, leading to dampness and the possible risk of clumping which can affect its effectiveness and structural integrity.


  • Most materials are environmentally friendly.
  • Budget-friendly.


  • Moisture sensitivity.


3. Expanded Polystyrene (EPS) Beads

As you can tell by its name, EPS beads are a unique, modern insulation option that looks like a tiny bead made with carbon polymer. Expanded polystyrene beads work by mixing them with a bonding agent before injecting the beads into the wall cavities. 

The beads settle into every nook and cranny, forming a cohesive insulating layer. The beads are also known for their moisture resistance, reducing the risk of dampness within the cavity walls. EPS is also recyclable, allowing the material to be repurposed into other products. 

Now, when discussing the drawbacks, the first factor we need to mention is problems with installation. While the process is simple, an incorrect installation or an inadequate bonding agent can lead to insulation failure. 

Also, over time, the beads can settle and shift, and the bonding agent may weaken, too, compromising the insulation’s effectiveness.


  • Straightforward installation process with minimal time.
  • Excellent insulation performance.
  • Reduced risk of water damage.


  •  The insulation can be ineffective if installed wrong.
  • The beads can shift and settle over time.


4. Cavity Wall Batts

This type of insulation is usually made of material like mineral wool that’s compressed into slabs of varying thickness. They’re most prevalent in new buildings and are loved for their water-resistant quality, which enhances their durability.

The slabs are designed to fit snugly against the cavity’s inner wall, guaranteeing space between the batts and the exterior walls. This design is necessary as it allows for little space for ventilation, which reduces dampness risks and, therefore, mould.

The drawback to cavity wall batts is that they might not offer the same level of insulation as some other materials. Also, because of the structural nature of cavity batts, they’re predominantly more suited for new builds or properties with ongoing renovations rather than retrofit projects.


  • Moisture resistance.
  • Some products are also first resistant.
  • Budget-friendly.


  • Might not offer the best insulation levels.
  • Better suited for new homes.

Benefits of Cavity Wall Insulation 

Now that you know the most popular types of cavity wall insulation, it’s time to look at what installation could offer you. Here are four main advantages:

1. Improved Energy Efficiency

The first noticeable benefit that cavity wall insulation provides is enhanced home energy efficiency. By filling up the gaps between the inner and outer walls with insulating materials, you reduce the rate at which heat escapes during the winter and enters during the summer. This is true regardless of the cavity wall insulation type you have.

So, the thermal barrier means your home requires less energy to maintain a comfortable temperature, making the building more efficient in its energy usage no matter the season!

2. Reduced Heating and Cooling Bills

As we mentioned, the new insulation barrier creates a balance in your home’s temperature, reducing your energy consumption. But what does it mean when it comes to bills?

Due to the general stability of your home, you won’t feel the need to keep turning up the dial on the heating in the colder months, or having to rely on cooling fans or AC when the temperatures rise in the summer months.. This reduced reliance on your heating and cooling systems directly translates to lower energy consumption and, consequently, lower energy bills.

As time goes on, the savings generated from the reduced bills can offset the initial cost of installing the insulation, making it a smart home improvement.

3. Lower Carbon Footprint

Now, we might’ve hammered this point a bit much, but again, the cavity wall insulation guarantees less energy consumption. In today’s environmentally-conscious world, having an energy-efficient home is a fantastic aspect, as less energy means a lower carbon footprint.

Since much of the energy supplied to homes is generated from fossil fuels, using less energy means less dependence on power plants and less carbon emission. In short, you play a crucial role in mitigating climate change by insulating your home! 

4. Extra Comfort

Finally, since insulation stops heat from escaping or entering your home at a rapid rate, the temperature change is significantly minimal. This stability guarantees comfort in the home which can also have positive health benefits..

Moreover, most insulation materials offer another extra perk: noise dampening. Because of the barrier they create, they effectively cut off any noise coming from the outside, making your home a quiet haven. 

Drawbacks of Cavity Wall Insulation

To make an informed decision about whether you should install cavity walls, you must consider both the benefits and potential drawbacks.

So, here are some of the main problems you might encounter:

1. Suitability Challenges 

One of the first problems you’ll encounter with cavity wall insulation is that it largely depends on the structural characteristics of your building. Specific insulation options, like cavity wall batts, are much better suited for homes undergoing serious renovations or old ones that can more easily incorporate these modifications.

This is because some insulation can be rigid and require specific conditions for installation that are more readily met during extensive renovation projects. Sadly, this can lead to increasing your budget to help facilitate the installation process.

2. Possible Moisture Penetration 

Another problem you can face is moisture penetration, especially in regions with high rainfall that can experience wind-drive rain. If the outer wall isn’t weatherproofed adequately or the insulation properly installed, the rainwater can seep through and dampen the material.

Of course, this can compromise its insulation properties, and lead to bigger issues like black mould and damp spots. When installing cavity wall insulation, you need to ensure that your outer walls are sound and without cracks..

Also, once you’ve picked out your favourite wall cavity, take a look at its cons and make sure it doesn’t let in rainwater or absorb water.

3. Difficult to Adjust

Though this might not be a big issue to some, once you install a cavity wall insulation, removing or replacing it can be costly. Of course, this is really only something you’ll have to do if something happens to affect the integrity of the insulating material, like shifting or absorbing water, or if a better option becomes available.

The difficulty or cost of removing or adjusting cavity wall insulation may discourage some homeowners from upgrading their insulation, but it is doable and recommended if your cavity wall insulation is already damaged. Your ineffective insulation will already be costing you money so it makes financial sense to remedy the problem. 

4. High Costs

Finally, the drawback that leaves most homeowners grimacing is the overall cost. While the material itself might not necessarily be overly expensive, it’s a job that really needs to be carried out by skilled professionals and requires specialised equipment.

Despite this, price shouldn’t be enough to put you off as you need to balance the immediate investment against the anticipated energy savings and increased comfort levels, as well as looking at possible grant funding that may be available to you. Adding insulation to your home can appear costly, but it’s a price your future energy bills will offset.

Frequently Asked Questions

Below, you’ll find a few popular questions many homeowners wondered about cavity wall insulation that’ll help you learn more about them.

What is the most sustainable cavity wall insulation?

When it comes to cavity wall insulation, glass wool is by far the most sustainable option. The material is made primarily from recycled glass, making it an eco-friendly choice that utilises waste material and reduces the demand for new raw resources.

What houses should not have cavity wall insulation?

Some homes might not be suitable for cavity wall insulation, such as solid-wall properties (usually pre-1920s), elevated properties or timber and steel-framed ones.However, it’s best to ask a professional to inspect your house before deciding this yourself. 

Why is my house so cold even with cavity wall insulation?

If you have a chilly home even after insulating the cavity wall then there’s possibly a problem with the insulation. Proper insulation should solidify your walls more by acting as a barrier and keeping heat from escaping. If this isn’t the case with your home, you should get a professional to inspect the existing insulation.

Final Words

So, have you decided which is the best cavity wall insulation for your home? If not, don’t rush! The team at Eco Grants can advise you on your insulation options, including the condition of your current insulation (if any), and if your home is suitable for cavity wall insulation. 

From mineral wool, and cavity batts to EPS bead and polyurethane foam, there are plenty of cavity wall options, each of which may be suitable depending on your home. Going with effective cavity wall insulation, you’ll be making an investment that will pay off in energy bill savings for many years to come.

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