Blown Cavity Wall Insulation: What Is It, Types & Costs

Around 71% of UK homes have cavity walls, yet nearly 29% lack proper insulation, leading to higher energy bills. With energy costs rising—Ofgem reports a 1.2% increase—upgrading to cavity insulation can significantly cut expenses.

Blow-in insulation UK is one of the most effective solutions, known for its reliability and excellent thermal performance. Properly installed insulation improves energy efficiency, making your home warmer and reducing heat loss.

This WhatCost guide will cover everything about blown cavity wall insulation, including materials, costs, and benefits. To get started, consult a professional. WhatCost makes it easy! Fill out our quick 30-second form to receive up to four free quotes from trusted insulation specialists in your area. Click below and start saving today!

Blown cavity wall insulation involves drilling 25mm holes into the walls and blowing in the chosen insulation material, which fills the gap between the internal and external walls—hence the name. Once the material is in place, the holes are professionally sealed. The entire process typically takes two to three hours to complete.

Loose fill cavity wall insulation requires specialised equipment, so it’s crucial to hire a CIGA-certified installer. Choosing a certified professional ensures proper installation and provides the added benefit of a 25-year guarantee, making this insulation a reliable and worthwhile investment.

Blown cavity wall insulation is a straightforward process that requires minimal effort and is quick to install. Knowing these steps is crucial in determining whether this installation method is suitable for your property and aligns with your properties. Here is a step-by-step guide on how blown in cavity wall insulation is installed:

The entire process usually takes two to three hours, depending on the size of the property, and should always be carried out by a certified professional to ensure quality and compliance.

Insulating your home offers numerous benefits, from lowering energy bills to creating a more comfortable living environment. Blown in cavity wall insulation is no exception—in fact, insulating your cavity walls is one of the most effective ways to improve your home’s energy efficiency. Here are the key benefits of blown-in cavity wall insulation:

With the current energy crisis in the UK and rising energy bills, cavity wall blown insulation is becoming increasingly appealing for homeowners. Savings on energy costs can vary by property size; larger homes may incur higher installation costs but also offer greater potential savings.

The savings in Northern Ireland differ slightly from the rest of the UK: 

There are several blown cavity wall insulation materials, each with advantages and disadvantages. Choosing the right blown-in cavity wall insulation is crucial for making an informed decision that will benefit your home and align with your preferences. Here are the most common loose fill cavity wall insulation materials available:

Mineral wool is a dense, fibre-based insulation material that effectively provides soundproofing and thermal insulation. However, its weight may limit its use in cavity walls with poor structural integrity. 

Composed of rock or glass, mineral wool costs between £13 and £17.50 per square meter and comes in forms such as batts, blankets, or loose fill. Rockwool cavity wall insulation offers an impressive R-value of 3.7 to 4.3 per inch, surpassing glass alternatives.

A key benefit of mineral wool is its exceptional fire resistance, making it the safest insulation choice for your home. It is also moisture-resistant, preventing mould and mildew growth.

EPS polystyrene beads, or expanded polystyrene beads, are popular in loose fill cavity wall insulation due to their excellent thermal performance, durability, and weather resistance. They are especially effective for blown-in cavity wall insulation, providing consistent coverage and eliminating gaps.

With an R-value of 2.6 to 3.3 per inch and a cost of around £10 per square meter, EPS beads offer solid thermal insulation. They are water-resistant, reducing dampness risk, and are flame- and smoke-resistant, making them safe for homes.

A key benefit is their long-term stability; they resist settling over time, ensuring effective insulation. However, as a petroleum-based product, they have environmental downsides, including harmful fumes during production. Some varieties are recyclable, providing a more eco-friendly option. Overall, EPS beads balance cost, durability, and energy efficiency, making them a practical choice for cavity wall insulation.

Cellulose is a loose fill cavity wall insulation made from recycled paper, providing an eco-friendly option for cavity wall insulation. Available in wet and dry forms, it costs about £10 per square meter and offers an R-value of 2.4 to 3.8 per inch. While its thermal performance is slightly lower than that of polyurethane foam or polystyrene beads, it remains an effective insulator.

One of its key advantages is sustainability, as it’s made from recycled materials and treated with boric acid for fire, pest, and mould resistance. However, cellulose can absorb moisture, which may reduce its effectiveness in damp conditions. It does not produce harmful off-gassing, making it a healthier indoor option. Overall, cellulose is a practical choice for eco-conscious homeowners.

Fibreglass is one of the most cost-effective insulation materials available, with an average cost of £10 per m2. Made from glass, it is available in blanket form (commonly called batts) and as loose fill, making it versatile for various applications. 

Fibreglass offers an R-value of 3 to 4 per inch. While it does not absorb water, fibreglass can retain moisture within its structure, which reduces its thermal performance and creates the potential for mould and mildew growth. 

Despite this drawback, it remains a reliable choice for blown cavity wall insulation. Fire resistance is another strong point of fibreglass—it can withstand temperatures up to 540°C, ensuring it will not contribute to the spread of fire in your home. Additionally, it is an effective soundproofing material, providing added benefits beyond thermal insulation.

Choosing the best blown cavity wall insulation material depends on your priorities, such as affordability, thermal efficiency, fire resistance, and environmental impact. Here’s a quick overview:

Selecting the right insulation is crucial for durability and comfort in your home. It can be overwhelming, but with the help of a trusted professional, you can find the perfect insulation tailored to your needs.

Don't let finding the right installer stress you out—WhatCost is here to help! Just take 30 seconds to fill out our form, and you'll receive up to four free quotes from top insulation specialists in your area. Click below to simplify your search and enhance your home's efficiency!

Blown cavity insulation costs typically range from £550 to £4,300, depending on property size, location, and insulation material. In areas like London, labour costs are higher due to the cost of living. Larger homes also incur greater expenses due to more materials and longer installation times. Below is a table outlining costs based on property type in England, Wales, and Scotland:

In Northern Ireland, the cost of cavity wall blown insulation are slightly cheaper than the rest of the UK:

Blown cavity insulation can be a significant expense, especially during times of high living costs. While the energy savings help offset the upfront investment, the initial cost may still be unaffordable for some. Fortunately, there are several cavity wall insulation grants available in the UK to help reduce the financial burden. 

To qualify for home insulation grants, you must meet specific eligibility criteria, making working with a certified professional essential. UK building regulations require grants to be used for professionally installed insulation, so DIY projects do not qualify.

Finding the right insulation specialist can be challenging, but WhatCost simplifies the process. Fill out our quick 30-second form, and we’ll connect you with up to four free quotes from top-rated experts in your area. Don’t wait—get started now!