top of page

Energy Saving Grants Blog

Stay up to date with the latest news related to Energy Saving Grants, energy ratings, Green Deal, and environmental issues effecting energy grants.

What is Cavity Wall Insulation? Benefits Unveiled

Cavity wall insulation is among the numerous methods to insulate your home. Through this informative guide, our primary focus is on understanding cavity wall insulation and its relevance to homeowners. Homeowners benefit from energy savings and cost reductions by opting for this insulation method.

Additionally, a significant advantage of cavity wall insulation is that it preserves the house's external appearance. So, there will be no discernible visual alterations for those retrofitting their homes. Within this discussion, we'll explore the core question of What is cavity wall insulation?, delve into its various types, and learn about the most effective ones, with their potential costs.

What is Cavity Wall Insulation?

What Is Cavity Wall Insulation?

Cavity wall insulation involves placing insulating materials in the space or "cavity" between a building's inner and outer walls. This insulation technique enhances a building's energy efficiency by minimizing heat escape through its walls.

With this approach, it's possible to decrease the heat loss of a building by an average of 30%. Consequently, this substantially drops in energy expenses and heightened energy conservation.

Cavity Wall Insulation: How it Works?

When a room is warm and separated from a colder environment by a wall, heat naturally transfers through the wall, attempting to balance the temperature. This would hypothetically lead to the interior and exterior having the same temperature.

However, in real-life scenarios, rooms are typically heated. As such, additional warmth is added when heat leaves through the wall, ensuring the room remains at a pleasant temperature.

The speed at which this thermal energy travels across the wall amplifies when the temperature difference is more pronounced, such as during a chilly winter.

Understanding cavity wall insulation: how it works reveals that this method acts as a thermal shield, significantly decelerating the heat's escape from a room. Consequently, with the diminished heat loss, there's less need to continuously heat the space to maintain a desired temperature.

Conversely, during summer, this insulation ensures the external heat doesn't penetrate the home's interior as quickly, reducing the reliance on cooling systems.

Hence, cavity wall insulation is pivotal in optimizing energy consumption throughout the year, reflecting positively on utility bills. Given its cost-effectiveness and the speed of its installation, it stands as a noteworthy consideration for homeowners.

What Materials Are Used In Cavity Wall Insulation?

Every building and surrounding environment demands specific insulation materials for its cavity walls, recognizing that what works optimally for one might not be the best for another. A diverse range of materials are available for this purpose:

  • Mineral Wool: This material is effective for thermal insulation and offers soundproofing qualities. Its resilience against fire and moisture further accentuates its suitability.

  • Expanded Polystyrene involves injecting tiny bead-like spheres into the cavity and filling it to ensure insulation. These beads are cost-effective and lightweight, boasting commendable thermal insulating traits. When fused with a binder during setup, they create a cohesive insulation layer.

  • Polyurethane Foam: Applied as a spray, this foam expands upon contact with the cavity and solidifies. It excels in providing heat insulation and acts as a barrier against air leaks.

  • Phenolic Foam: Crafted from phenol-formaldehyde resin, this rigid foam stands out for its superior insulation abilities and minimal thermal conductivity. Its inherent resistance to both moisture and fire makes it an ideal choice for cavity wall insulation.

Types Of Cavity Wall Insulation

Various cavity wall insulation options are available, and the optimal choice depends on your budget and the nature of your building.

Cavity Wall Insulation Boards: These are great for new constructions. Notably thin, these boards still deliver outstanding thermal conductivity. This means you can achieve the desired U-values without a thick insulation layer.

Pumped Cavity Wall Insulation: This technique involves blowing insulation into the building via tiny wall openings. It's the go-to method for retrofitting projects where traditional cavity wall insulation methods aren't feasible due to pre-existing wall structures.

Mineral Fibre Cavity Wall Insulation: Suitable for new developments, mineral fibre stands as an alternative to insulation boards. However, it possesses a slightly inferior thermal conductivity in comparison. As a result, a more substantial quantity is necessary to hit the targeted U-value.

How To Install Cavity Wall Insulation?

Typically, installing cavity wall insulation involves drilling various small holes, each roughly 25mm in diameter (similar to the size of a ten pence coin), into the wall's mortar at uniform distances.

Through these holes, the insulation material is then injected into the cavity. The drilled holes are sealed and filled after the insulation is successfully blown in. Some professionals also use a telescopic lance system for walls that present access challenges to facilitate the process.

In the case of new constructions, rigid insulation boards are commonly integrated into the wall cavities during the building phase.

How Much Does Cavity Wall Insulation Cost In The UK? How Much Will You Save?

The cost of cavity wall insulation in the UK generally falls between £25 and £30 for every square meter of wall. The total expense primarily depends on the building's size that you intend to insulate.

That said, there's an alternative to lower this cost. The ECO4 scheme offers cavity wall insulation grants that could cover the total! You might not have to spend a penny if you fit the eligibility criteria and your property is suitable for the insulation.

Considering the savings from cavity wall insulation, the financial benefits fluctuate based on individual properties. However, for a typical three-bedroom house, energy savings post insulation can be estimated at around £250 annually.

Given an installation expenditure ranging from £600 to £1000, the savings generated from the cost of cavity wall insulation in the UK would typically offset the initial investment in less than four years.

Add the table (

Benefits Of Cavity Wall Insulation

  • Cavity wall insulation can enhance home heating efficiency, saving around £250-300 annually for an average 3-bedroom house.

  • Investing in cavity wall insulation sees a payback in 3-4 years through reduced heating expenses.

  • The Energy Saving Trust states that cavity wall insulation can cut carbon dioxide emissions by 560kg.

  • Cavity wall installation accredited by the CIGA (Cavity Insulation Guarantee Agency) comes with a 25-year guarantee.

Limitations Of Cavity Wall Insulation

  • Cavity wall insulation might not be appropriate for homes with walls exposed to heavy wind-driven rain.

  • Before installing insulation, if your home has damp issues, consult a professional surveyor for an assessment.

Does Cavity Wall Insulation Cause Damp?

Cavity wall insulation doesn't induce dampness; contrarily, it can be a preventive measure against moisture in a structure.

Nevertheless, a comprehensive building inspection is crucial to detect and rectify any existing dampness issues before installing insulation. Installing insulation in a building already plagued with dampness can worsen the condition.

Issues related to dampness, such as moisture entrapped in the wall cavity before the installation, can lead to permanent moisture entrapment. Therefore, ensuring that a qualified and seasoned professional installs your insulation is imperative to avoid such problems.

Is My Home Suitable To Install Cavity Wall Insulation?

What is cavity wall insulation, and is my home qualified for it?" is a common question among homeowners. Generally, your home might be a good candidate for cavity wall insulation if:

  • Your external walls have an unfilled cavity.

  • The masonry or brickwork is well-maintained.

  • The cavity's width is a minimum of 35mm, or 50mm, for certain insulation types.

However, understanding cavity wall insulation: how it works is crucial, as there are situations where it shouldn't be used, especially if:

  • There are maintenance issues or structural problems like wall cracks.

  • There are visible signs of rising or penetrating dampness.

  • The cavities are dirty, wall ties are unclean, or there's construction debris within the cavity.

  • The walls are in exposed locations, especially vulnerable to severe weather conditions and persistent rain.

  • Guttering is blocked or overflowing.

In such instances, cavity wall insulation might not be the ideal choice unless corrective measures are feasible.


In conclusion, understanding the intricacies of cavity wall insulation is crucial for homeowners looking to enhance their home's energy efficiency.

While many properties in the UK can benefit from this insulation method, certain conditions and structural factors must be considered before installation. Moreover, while the initial cavity wall insulation cost in the UK might seem like an investment, the long-term savings on heating bills and environmental impact make it worthwhile.

It's essential to consider the immediate costs and the long-term benefits when evaluating the actual value of such an investment in your home's future.

Read more: What Is Loft Insulation? How Does Loft Insulation Work?

Featured Posts
Follow Us
  • Energy Saving Grants on Facebook
  • Energy Saving Grants on Twitter
  • Energy Saving Grants on Pinterest
  • Energy Saving Grants on Instagram
Check Your Eligibility Using Our Grant Checker

Please ensure that all information provided below is 100% accurate. Any errors in your personal information could delay or prevent you qualifying for a government funded grant.

Please note that you do not necessarily need to be in receipt of tax credits or benefits as we still may be able to obtain funding for you via your Council or through other funding schemes.

bottom of page