The 5 best cavity wall insulation options for your home 2024

• Cavity wall insulation materials range in price from £5-£75 per square metre
• Mineral wool is the best option for older properties
• Rigid insulation boards or cavity batts are the best option for newer properties

There are many ways to insulate your property’s cavity walls (check out the costs of spray foam insulation, for instance), but some ways are better than others.

The right way for you will depend on the size of your property, how much heat you’re currently losing and what you can afford.

Whatever you choose, cavity wall insulation will help you save money and energy.

After all, about a third of all the heat lost in a home escapes through the walls (Energy Saving Trust, 2023).

In this article, we share the best cavity wall insulation options to consider for your home.

If you’re considering cavity wall insulation, you can find the best deals by simply popping a few details in this quick form.

Once we have these, we’ll put you in touch with our trusted insulation installers, who will provide you with their top deals.

What are the best types of cavity wall insulation?

The suitability of each cavity wall insulation type depends on various factors, such as the construction of your home, the climate in your area, and your budget.

Here are some of the most commonly used types of cavity wall insulation:

• Spray foam insulation – a mixture of polyol resin and isocyanate that create a foam, which is sprayed into cavity walls and expands to fit the space and form a seal
• Mineral wool – made from natural or synthetic fibres derived from minerals such as rock or glass
• Beads and granules – small foam particles typically made of expanded polystyrene (EPS)
• Rigid insulation boards – panels typically made from expanded polystyrene (EPS), extruded polystyrene (XPS), or polyisocyanurate (PIR)
• Cavity batts – mineral wool that has been compressed to form slabs, covered with a water-resistant film

What is the most efficient type of cavity wall insulation?

The most efficient cavity wall insulation is spray foam – it expands upon application creating an airtight seal, providing a high level of thermal resistance with a longer life than other forms of insulation.

However, it is on the expensive side, so think very carefully about what you can afford.

Want to see if spray foam is right for you? Check out our guide: Is Spray Foam Insulation Worth It?

What insulation should I choose for a wall cavity?

The type of insulation you should use in a cavity wall depends on several factors including the age of your home, your local climate, and your budget.

Older properties benefit from mineral wool which is breathable and can be installed without any obvious aesthetic changes.

Newer properties may be better using rigid insulation boards that can enhance the structural integrity of the walls and are typically moisture-resistant.

Are there any houses that shouldn’t have cavity wall insulation?

Houses that should not have cavity wall insulation include timber-framed properties, steel-framed properties, properties experiencing issues with penetrative damp, and properties with a cavity wall under 50mm or over 150mm.

Which cavity wall insulation should I get?

The type of cavity wall insulation you should choose depends on various factors. These include the specific characteristics of your property, your insulation goals, budget, and any other considerations you believe important such as soundproofing or fire resistance.

Spray foam insulation

Spray foam insulation is applied using a spray application method. It consists of a mixture of two components, polyol resin and isocyanate, which react and expand upon contact to form a foam.

It’s available in two types: open-cell foam and closed-cell foam. Open-cell foam is softer and less dense, while closed-cell foam is denser and provides a higher level of insulation. The foam is sprayed onto the designated areas, conforming to the shape of the space being insulated.

The foam adheres to the surface, creating a continuous layer of insulation that effectively reduces heat loss or gain and helps to prevent moisture-related issues such as condensation.

The average price of spray foam insulation is £20-£50 per square metre.

Mineral wool

Mineral wool is an insulation material made from natural or synthetic fibres derived from minerals such as rock or glass. It works by trapping air within its fibres, which helps to reduce heat transfer.

Mineral wool insulation is installed by blowing the material into the cavity using specialist equipment. The material fills the voids, providing an effective thermal barrier. It can significantly reduce heat loss through the walls, improving the energy efficiency of a building. It also offers soundproofing benefits by absorbing sound waves.

The average price of mineral wool is £13-£17.50 per square metre.

Beads and granules

Beads and granules insulation utilises small foam particles to fill the gaps and voids in the wall cavity. These particles are typically made of expanded polystyrene (EPS). The installation process involves drilling small holes into the external walls of the property at regular intervals.

Through these holes, the foam particles are blown into the cavity using an injection system. As the particles are injected, they disperse and interlock, forming a continuous layer of insulation that fills the available space and reduces heat transfer. The drilled holes are then filled to restore the appearance of the walls.

The average price of beads and granules for cavity wall insulation is £18-£22 per square metre.

Rigid insulation boards

Rigid insulation boards are typically made of materials such as expanded polystyrene (EPS), extruded polystyrene (XPS), or polyisocyanurate (PIR). The boards are fixed to the surface of the wall or other areas using adhesive, mechanical fixings, or a combination of both.

The boards are cut to fit the required dimensions and then secured in place. Joints between the boards are sealed to ensure a continuous insulation layer. They work by reducing heat transfer through conduction. The closed-cell structure of the boards traps air, preventing the movement of heat.

The cost of rigid insulation boards vary slightly depending on the material used. Typically per square metre EPS boards are around £10, PIR boards cost about £5-£15 and XPS boards are £10-£15.

Cavity batts

Cavity batts are typically used in new builds or extensions where the cavity width allows for full-fill insulation. The batts are slabs of mineral wool that have been compressed together and covered with a water-resistant film. The slabs are fitted tightly together to fill the entire void, reducing heat transfer through the walls.

The typical cost for cavity batts ranges anywhere from £12 to £75 per square metre depending on the thickness of the batts.

Is cavity wall insulation right for my home?

The answer to to this question depends on various factors. Firstly it is important to make sure that your home has a cavity that is suitable for insulation.

A wall is suitable for insulation if it has a cavity at least 50mm wide.

It’s essential to check your property meets the necessary building regulations and requirements for cavity wall insulation.

Factors such as exposure to wind-driven rain, brickwork in bad condition, and the presence of damp or structural issues should be considered.

If your home meets the requirements and has poor insulation (for example you experience issues with heat loss, cold spots, or high energy bills) then you could certainly benefit from cavity wall insulation.

What’s the best cavity wall insulation for older properties?

The best type of cavity wall insulation for older properties is mineral wool.

This is because older properties are often more prone to issues such as moisture and condensation, which mineral wool is designed to prevent.

Mineral wool is breathable, allowing moisture to pass through the wall while still providing insulation. This helps in maintaining a healthy and dry environment within the property.

Mineral wool also has excellent fire-resistant properties, making it a safe choice for older properties. It is non-combustible and can act as a fire barrier, reducing the risk of fire spread within the cavity walls.

It also has good soundproofing properties, which can be an added benefit in older properties that may have thinner walls.

As mineral wool is installed through small, drilled holes, it minimises any impact on the external appearance of the property, preserving its original appearance.

What’s the best cavity wall insulation for newer properties?

For newer properties, one of the best types of cavity wall insulation is rigid insulation boards.

They have excellent thermal insulation properties and can improve the structural integrity of the walls as they are rigid and provide additional support.

They are typically moisture-resistant too, particularly beneficial for newer properties where maintaining a dry and moisture-free cavity is important to avoid potential future issues such as damp or mould.

Rigid insulation boards are straightforward to install, especially in properties with accessible cavities. This can save time during the installation process.

For homes that aren’t built yet, cavity batts are worth considering due to their superior fire resistance.

How do I get started?      

There are various options when it comes to cavity wall insulation – and the first step to take is understand exactly what you need.

Consulting with insulation professionals or surveyors should be the first step you take as they can help evaluate the suitability of different insulation types and recommend the most appropriate solution for your home.

To find the best deals for spray foam insulation, we can put you in touch with our trusted insulation installers. Simply add a few details into this quick form and they’ll get in touch directly with their best deals.

Summary

• Cavity wall insulation will save you money and energy, but it’s important to understand what you can afford before you get started.
• Spray foam insulation is the most efficient, but it is also quite expensive.
• If you have an older property, mineral wool will probably work best.
• Houses that are timber-framed, steel-framed or experiencing penetrative damp shouldn’t have cavity wall insulation. Nor should those with a cavity wall under 50mm or over 150mm.
• If you’re considering cavity wall insulation, you can find the best deals by simply popping a few details in this quick form.