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Cavity Wall Insulation Cost – Everything you need to know

In the UK, houses built before the 1920s often have solid walls. From the 1920s onwards, homes tend to have cavity walls, which are also called Hollow walls. 

How can cavity walls and a good insulation solution save more money on your bills? Read on and get in touch with us to learn more.


What’s a cavity wall? 

A cavity wall consists of two layers and a gap – or cavity – between them. The inner wall is called the internal leaf and the outer wall is called the external leaf. 

Typically, the two walls have the same thickness of at least 10 mm. Sometimes, the internal leaf may be a little thicker compared to the external one. The cavity between them is between 4 – 10 cm. 

The two leaves should have at least 10 mm of thickness and typically, they have the same thickness. However, sometimes, the internal leaf may be a little thicker. The cavity should be between 4 – 10 cm. Metal ties or links are used to connect the two layers of the wall. 

Thanks to the cavity between the two walls, cavity walls can reduce heat transmission, thus, saving more money on your heating bills. 


How can I know I have cavity walls?

There are several ways to find out the kind of wall at your home. As a general rule of thumb, homes built before the 1920s were constructed with solid walls. That means if your home was built after that period, it should have cavity walls. 

Another way to check your wall is to look at the pattern of the bricks. Cavity walls usually have an even pattern and brinks are arranged lengthways. Meanwhile, on solid walls, bricks are put in an alternative pattern, making it look like the length of the bricks is not even.

You can also contact professional traders or the local authority’s building control department who will be able to help you find out if you have cavity walls at home.


The benefits of insulation for cavity wall

The gap between the two walls is filled with insulation materials to prevent heat loss in the property. The most common materials used for cavity wall insulation are mineral wool, polystyrene balls and expanding foam. 

As heat loss is mainly caused by poor-quality wall insulation, upgrading the insulation for your cavity walls is a smart solution to save more money on your energy bills in a long run. Additionally, according to Energy Saving Trust, it will take only around five years for cavity wall insulation to pay for itself. In short, investing in cavity wall insulation will bring you a warmer home and lower energy bills. 

The advantage of preventing heat loss of cavity walls will help you improve the energy performance of your property which is essential for landlords who want to sell or rent out their houses or flats. Apart from that, cavity walls with high-quality insulation also reduce dampness and outer efflorescence, diminish the weight on the foundation and act as an effective sound insulator.

It’s also worth mentioning that installing insulation for cavity walls is simple and quick and can normally be completed within two hours. Furthermore, it doesn’t disrupt other activities at your place.


Are my cavity walls qualified for insulation?

If your home was built only around 20 years ago, it has probably been insulated. You can have a proper borescope inspection with a registered installer. They will drill a small hole in your external wall and check if the gap between the walls is filled with insulation material. Otherwise, you can contact your local authority’s building control department for their consultancy and help. 

In case you need to install insulation for your wall, the first step is to work with a registered installer to conduct a survey of the condition of your living space. The instalment can be started immediately if your home meets these criteria:

The cavity is not filled yet. 

The cavity is 50 mm or wider. 

There is no rubber in the cavity.

The masonry is in good condition.

Both the internal and external leaves are not exposed to driving rain.

The property is not exposed to the harm of flooding.

Based on the outcome of the survey, the installer will plan the next step, which can be either deciding on the type of insulation material or undertaking additional improvements for your walls before the insulation instalment.

If all the criteria above are met, the cavity can be filled with either mineral wool or polystyrene beads.

If the cavities between your walls appear to be narrow or uneven, that may lead to a risk of flooding. In that case, polyurethane foam should be the best insulation material and you should reach out to a specialist foam insulation installer to survey your home before the instalment. 

Damp patches should be removed before you start your work on the wall insulation. 

Joint walls will require extra work in advance. If your external leaf is joined by another house, a cavity barrier will be needed to ensure your neighbour won’t be affected by your insulation instalment. 

If you live in a flat, you will need the agreement of everyone sharing the same block with you before being able to install the wall insulation.


How can I find an installer?

In the UK, qualified installers must be members of The National Insulation Association (NIA), The Cavity Insulation Guarantee Agency (CIGA) or The British Board of Agrément (BBA).

There are two factors you need to check: firstly, ensure that the installer is signed up to a code of professional practice, and secondly, make sure that the installation is guaranteed by CIGA or an independent insurance-backed guarantee. 


Types and costs of insulation instalment for cavity walls

The total cost to install insulation for cavity walls depends on different factors. For example, insulation for a detached property tends to be more expensive than insulation costs for a mid-terraced house or a bungalow of the same size.

You should contact several installers to compare their quote and coordinate with them to survey your place to find out the final costs.

In terms of insulation materials:

Blown mineral fibre consisting of fibreglass or mineral wool is the most common type of insulation for cavity walls. They are tufts that are expandable after being blown in, filling up the cavity. If installed correctly, it can remain for the lifetime of your property.
The restriction is that mineral fibre can be used for only cavities with standard or large size. If the gap is below 50 mm, the insulation material may be patchy. Furthermore, it’s strictly to keep mineral fibre dry before installing it to maintain the quality of the material.
Averagely, it takes around £11 per sqm to install mineral fibre insulation.

For narrow cavities, you can consider using polystyrene (EPS), which consists of small beads blown into the cavity by compressed air and a mix of adhesives. This kind of material comes with several benefits: the beads can easily fill up the gap, creating solid insulation layers without gaps. At the same time, it still allows moisture to drain through, reducing the risk of built-up dampness.
The disadvantage of EPS is that loose granules may escape through airbricks, lowering the quality of the insulation.
This kind of insulation costs approximately £11.50 per sqm. 

Polyurethane (PU) foam is the most expensive insulation material for cavity walls as it’s also the most high-quality material. It is pumped into cavities, filling up the space and strongly supporting the strength of complex structures where wall ties are corroded or flood risk is high.
The average cost for insulation with polyurethane foam is around £28 per sqm.

What if I have problems after the insulation instalment?

After installing insulation for your cavity walls, you may face unexpected situations, such as the appearance of damp and mould. The first option should be contacting your installer and having them revisit your property to find out the cause of the problem. If it’s the installation, they should offer remedial work or remove and reinstall the insulation. 

Make sure to check if you’re still covered by the 25-year CIGA Guarantee that allows you to fix the problems without paying extra costs. If you don’t have a CIGA Guarantee, an independent insurance-backed guarantee can also offer the same support. 

In case you can’t get any assistance from CIGA and any independent insurance-backed guarantees, contact a company that provides paid fixing service. It’s important to work with reliable specialists accredited with a cavity wall insulation scheme like CIGA or BBA.

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