21st Nov 2022 -

Whether you are looking to install cavity wall insulation within a building project, or within your own home, the benefits provided make it all but essential in modern buildings. Houses built after the 1920s are likely to have cavity walls, brick walls built as two layers with a space between them. Older houses are likely to only have a single solid wall, making them ineligible. As about a third of lost heat in a house goes through walls, ensuring you have sufficient cavity wall insulation should be a priority. Insulation of your cavity walls will save energy for homeowners, keep their homes warm, and save on heating bills. Thoroughly insulating cavity walls makes them more environmentally effective, reducing the amount of heating needed.

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In this guide from Building Materials Nationwide, we’ll take a look at your options in terms of cavity wall insulation, both as a refurbishment and within a new build. Then we’ll look at the cavity wall insulation costs for buying and installing within a home, including the cost per metre squared. We’ll also look at a government scheme that could completely cover the costs of your cavity wall insulation.

Your Options in Cavity Wall Insulation

In a newly built property, there is a wide range of traditional thermal insulation products available. There are boards, rolls, slabs and batts, many designed specifically to be used within a cavity wall, usually fitting between wall ties. These are installed during the building process, offering high-quality insulation to homeowners.

For a building refurbishment, these insulation materials will not be installable without removing a wall, so a method called filling is almost always used. This involves drilling small holes into a cavity wall (normally the outside wall to avoid interfering with any interior decoration or dry lining) and injecting an insulating material into the cavity, before resealing the holes. Cavity barriers are used within semi-detached or terraced houses, inserted into the dividing line to contain the insulation within your home. There are a variety of options for what can be blown into your cavity walls, such as mineral wool, beads or granules, and foamed insulants.

Mineral Wools

Mineral wools, such as glass or rock wool, will be treated with a binder and water repellent during the manufacturing process. Blown mineral wools are non-combustible, offering effective thermal insulation. They have been used within the UK for over 50 years, and are designed to last as long as a building lasts.

Polystyrene Beads

Polystyrene beads are another choice for blown cavity wall insulation. These beads are coated with a binding agent or adhesive, holding them in place once blown into a cavity. They can be used in thinner cavity walls, and in properties built from stone (which blown fibre insulation can struggle to evenly fill). Polystyrene beads offer good thermal insulation and water resistance. 

Polyurethane Injected Foam

Historically Urea Formaldehyde foam was used as a cavity wall filling, but degradation and health issues mean that it is not used anymore. Polyurethane foam is the most expensive filling, but offers excellent thermal insulation and strength, bonding inner and outer walls together. It can be used within difficult stone walls, expanding to fill all voids. Polyurethane foam also offers great water resistance.

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Cavity Wall Insulation Isn’t for Everyone

There are some situations where your home may be unsuitable for cavity wall insulation installation. If your home is in an area with severe levels of wind-driven rain, or the outer walls of your home are in poor condition, rain can penetrate the external walls of your house, crossing the cavity wall insulation and causing dampness within your inner walls. In these cases, you will have to have the cavity wall insulation removed, which is a very costly process. If you are worried that your home may be unsuitable for pumped cavity wall insulation, it may be worth hiring a chartered surveyor to assess your walls before opting for filled insulation.

The Cost of Fitting Cavity Wall Insulation in the UK

Traditional insulation for cavity walls can be bought as single boards or rolls, allowing you to measure and buy the necessary amount to fill the cavity walls within a newly built property. At Building Materials Nationwide, we have a range of boards, slabs, batts, and Celotex boards in stock on our website. While prices are subject to change, our cheapest boards are around £10 for a 1.2m by 0.455m board, our cheapest slabs are around £19 for a 1.2m by 0.455m slab. Our lowest-priced insulation batt is around £32 for a 1.2m x 0.455m slab, and our lowest-priced Celotex board is around £4.50 for a 1.2m x 0.45 board.

The labour cost of blown insulation will depend on the size of your house. Blown cavity wall insulation is not a time-consuming process, never taking more than a day. For a smaller flat, you can expect the insulation job to take between 1 and 2 hours and cost £50-£100. A detached one-floor house will take between 3 and 4 hours and cost about £150-£200. A terraced house or a semi-detached house will take between 2-3 hours, costing between £100 and £150 for filling. A detached house will take between 3 and 4 hours, costing £150 to £200.

Cavity Wall Insulation Costs Per M2 in the UK

While they can only be bought as larger boards, based on the current lowest prices, the cost per m2 of a cavity insulation board will be around £18.30. The cost of an insulation slab will start at about £34.70 per m2. Our lowest-priced insulation batts will cost about £58.60 per m2. Finally, our range of Celotex insulation boards will start at around £8.20 per m2.

Bearing in mind that you will not be able to install them yourself unless you own specialist equipment, the costs of mineral wool will be about £13-18 per metre2. Expanding Polystyrene Beads will cost between £18-22 per metre2. Polyurethane Foam costs about £22-26 per meter2.

Averaging labour and material costs for blown cavity wall insulation you’ll be looking at about £300-£350 for a smaller flat. The average cost of cavity wall insulation for a detached single-story house will be about £400-£450. For a terraced house, you’ll be spending around £350-£400. A semi-detached house will cost around £450-£500 for cavity wall insulation. A detached house will be between £700-£750 for blown cavity wall insulation. These costs may rise in older houses with complex walls, which may require the more expensive insulation filling. While this is not a cheap process by any means, it will be cost-effective over its lifespan, saving on energy bills by increasing the energy efficiency of your house.

If you or your home meet certain criteria you may be eligible for energy company obligation grants. Under this scheme, energy companies can offer up to £1000 for cavity wall insulation from energy companies. Energy suppliers serving over 150,000 customers are obligated to offer these grants through the scheme. While smaller companies have more limited obligations, if you are looking at insulating cavity walls in a house you own, you should contact your energy company before paying for the work yourself.

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Our Range of Cavity Wall Insulation For Sale

At Building Materials Nationwide, we have a range of solid cavity wall insulation for sale. We aim to remove the stress that so often comes with ordering building supplies, offering a one-stop solution; a great range of products, sold at competitive prices, with UK-wide delivery options. Through our website, we have a comprehensive selection of cavity wall insulation. We offer Boards, Slabs, Batts, and Celotex Boards for sale.

We also have a range of useful guides available through our website. For further information on insulation, why not read our guide to making your home more energy efficient, or our top tips on how to insulate a garage.

For our customers in the trades, we also offer trade accounts. Opening a trade account will gain you access to a dedicated account manager, who’ll communicate with you via phone or email. Your dedicated account manager will be able to assist you with large or unusual orders, and even be able to source products not listed on our website through our wide network. If you’re in the trades, sign up for a trade account through our website today, gaining access to our full product range, our express delivery options, and your own dedicated account manager.