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A guide to cavity wall insulation

In this series of retrofit measures blogs, we’ll be explaining different retrofit measures which can improve the energy efficiency of homes – reducing energy usage to cut energy bills and carbon emissions, and improve the comfort of your home.

We’ll include information on how the measure works, what types of homes it may be right for, what installation looks like, and more. In this post we’re looking at cavity wall insulation.

What is cavity wall insulation?

In uninsulated homes, around a third of heat loss is through the walls. This is particularly an issue in homes with cavity walls – which are made up of two walls (the outer usually brick; the inner usually brick or concrete) with a gap between them. Cavity wall insulation reduces this heat loss by filling the gap between the two walls – the ‘cavity’ with insulating material which prevents or reduces the leakage of heat.

How does cavity wall insulation work?

The most common method for fitting cavity wall insulation is for insulation material to be injected into the cavity – usually mineral wool, polystyrene beads, or polyurethane foam. This is done by drilling small holes in the outside walls at various intervals, injecting the material through the holes, and then filling the holes back up so they are not noticeable.

This procedure must be done by a professional and reputable installer to ensure it does not cause issues. If you work with Cosy Homes Oxfordshire on your home retrofit you’ll have access to our network of trusted contractors, who we will contact and manage for you.

What types of home does cavity wall insulation suit?

Cavity wall insulation is only relevant for homes which have cavity walls. If your home was built after the 1920s it will likely have cavity walls. If your home was built before 1920 it will probably have solid walls, and so solid wall insulation is more relevant for you.

Some homes with cavity walls will already have them insulated – it was common practice from the 1990s onwards to add insulation into cavity walls during construction.

Cavity wall insulation is not suitable for flats, unless you have agreement from the owners of all flats in your block to insulate the whole block.

If you aren’t sure what type of walls your home has, Cosy Homes Oxfordshire can help with that through our home assessment and Whole House Plan service.

What are the expected costs and savings?

As with any retrofit measure, the potential carbon and cost savings vary depending on the type and size of your home. Cavity wall insulation is a relatively simple measure which makes a big difference, and can reduce heat loss by up to a third – so it’s likely you can make substantial savings within 5 years of the insulation being installed.

The Energy Savings Trust predicts costs and savings as below (April 2019 data). Please note that you might be able to reduce these costs by carrying out the work at the same time as other home retrofit improvements through our Whole House Plan approach.

 Detached houseSemi-detached houseMid terraceBungalowFlat
Typical cost (£)£610£475£390£460£345
Energy bill savings (£/year)£280£165£105£110£85
Carbon emissions diverted (kgCO2/year)1150kg680kg430kg460kg335kg

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