Blown Cavity Wall Insulation: A UK Guide

Cavity walls are commonly found throughout the UK, making up nearly three-quarters of all properties. These walls consist of an inner and outer wall with a cavity or space in between to prevent moisture ingress. However, this cavity space should also be insulated to boost your home’s thermal efficiency.

A popular method of insulating cavity walls is through blown in insulation, which consists of a group of materials such as mineral wool, fibreglass, cellulose, and EPS polystyrene beads. This complete guide by GreenMatch UK will give you everything you need to know to make the right choice for your household.

Ready to get cavity wall insulation? Let GreenMatch UK solve all your problems. Through our nationwide network of pre-vetted installers, we can send you up to 3 free home-tailored quotes completely free of charges and obligations. Click the button below to begin! 

Blown cavity wall insulation fills the hollow space between your home's exterior walls with loose-fill insulation material. Here’s how the installation process takes place:

The entire process of cavity insulation takes only 1 - 2 hours, is non-invasive, and will leave your home's facade completely unchanged, making it a highly efficient means of insulating your walls. 

While the initial investment for cavity wall insulation may seem hefty, blown cavity wall insulation has plenty of benefits that justify the price tag. Here are just some of the key perks you can expect to enjoy:

Beyond the basics, you may be wondering just how much you could potentially save with cavity wall insulation. Take a look at the average annual savings per home type in the UK and in Northern Ireland:

Several blown insulation materials on the market are suited for cavity wall insulation. Each comes with its own price ranges, pros, cons, and properties worth considering. 

Regardless, all blown insulation materials are installed in the same manner; by a professional using industry equipment to inject material into the cavity space through drilled holes.

To get a better idea of what insulation material is best suited for your needs, let’s start by first taking a look at each material a bit more in-depth, as well as blown cavity wall insulation cost per m2 of material.

Mineral wool cavity wall insulation is one of the most popular on the market. Due to its relative affordability, availability and versatility, it makes for a very worthy option. Costing an affordable £13 - £17.5 per m2. Mineral wool is usually made from rock or glass and can be found as batts of blankets, or as loose fill used for blown in insulation, such as for cavity walls. Rockwool cavity wall insulation tends to perform better than glass.

Mineral wool also exhibits an impressive r-value range of around 2.5 - 3.3 m²K/W depending on the opted density of the material, with rockwool cavity insulation on the higher end of the spectrum. It is also hydrophobic, meaning it does not absorb water and is even flame and smoke-resistant.

EPS polystyrene beads are highly effective small spheres of polystyrene that have taken the insulation market by storm. These cavity wall insulation beads have highly impressive thermal capabilities, durability, and resistance to weathering making them a great long-term choice for blown cavity wall insulation.

With an r-value of 2.6 - 3.3 m²K/W, EPS polystyrene beads cost around £10 per m2 of material. They are also moisture, flame and smoke resistant, making them a safe household choice. 

As a downside, EPS polystyrene is a synthetic material that can release harmful fumes during production but can also be recycled into new polymer products after use.

Cellulose is perhaps one of the most sustainable and environmentally friendly blown fibre insulation options available on the market today. Made from recycled paper and wood products, cellulose only costs around £10 - £12 per m2, but boasts an impressive r-value of 2.4 - 2.8 m²K/W, making it a quite effective insulator.

As a downside, cellulose does not boast the same hydrophobic properties as some previously mentioned materials due to being composed of paper and wood, but as an advantage, cellulose does not produce harmful off-gassing during or after installation.

Fibreglass, much like mineral wool, can be found as batts of blankets or as loose-fill insulation to be injected into cavity walls. Made from recycled glass, it is relatively sustainable and disposable after use. 

Fibreglass costs around £10 per m2, but boasts an r-value range of 2.2 - 4.3 m²K/W, giving it an impressive cost-to-thermal efficiency balance. 

The best-blown cavity wall insulation will depend on several factors, such as what a customer considers the best qualities for an insulation material. 

For those looking for the cheapest blown cavity wall insulation material, then options such as fibreglass emerge as a great option. Alongside its smaller price tag, it still boasts an impressive r-value and moisture-resistant qualities.

For those looking for the most sustainable blown cavity wall insulation material, then cellulose is likely your best bet. It may not be as impressive in its properties, but it is entirely produced from recycled paper and wood waste, fully non-toxic, and can be recycled with ease.

For the most thermally efficient blown cavity wall insulation material, EPS polystyrene beads stand out as the top contender. With their high r-value, durable properties and robustness, polystyrene beads can provide sustained thermal comfort to a home for decades.

According to Energy Saving Trust UK, the average cost of blown cavity fill insulation for a standard UK detached house is around £4,600 for a full job, including materials and labour costs. However, this cost can vary depending on the type of property you have, and the insulation material you opt for.

Below is a summary of the average costs of a full cavity wall insulation per property type:

While cavity wall insulation, or wall insulation in general, tends to be more expensive than other home insulation upgrades, there’s a big chance you can get some assistance on the cost with some cavity wall insulation grants!

Luckily, the UK government has launched two key grant schemes to help fuel-poor, low-income, and energy-inefficient households with home insulation upgrades. These are the Great British Insulation Scheme (GBIS) and the Energy Company Obligation (ECO4). 

Both home insulation grant schemes prioritise homeowners and renters who fall into the low-income group. Some indicators of those who belong in this bracket are:

In addition, the Energy Performance Certificate (EPC) rating of a house can be a factor in whether you qualify or not for assistance. An EPC rating tells you how energy efficient your home is, rated from A (most efficient) to G (least efficient). Homeowners with an EPC rating below D can generally qualify for assistance. 

Deciding to insulate your cavity walls is a great step, but the real struggle is finding the right blown cavity wall insulation installers near you. With the endless choices, researching and vetting each company can have you stuck in an endless loop with no bargain in sight for insulating your home. Luckily, GreenMatch UK can help you out.

Simply fill in our 30-second online form, and we’ll send you up to 3 free home-tailored quotes straight from our nationwide network of professionals. The best part? Our services are completely free of charges and obligations. Click the button below to begin!