Cavity Wall Insulation — Stop Heat Escaping Through Your Walls

Around a third of all heat lost in an uninsulated home escapes through the walls. Cavity wall insulation fills the gap and keeps your home warmer for less.

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£310

Potential annual savings

Typical cost: £400 – £700

With UK energy bills remaining high under the current price cap, the 35% of heat that escapes through uninsulated walls represents a significant and avoidable cost. Most homes built after 1920 have cavity walls — two layers of brick with a gap between them — that can be filled with insulating material. Cavity wall insulation is one of the most effective ways to reduce heating demand, typically saving around £310 per year and paying for itself within two to three years.

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Potential annual saving

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Typical installation cost

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Average payback period

Wall heat loss prevented

What Is Cavity Wall?

Cavity wall insulation involves injecting insulating material into the gap (cavity) between the inner and outer leaves of your external walls. The most common materials used are mineral wool fibre, polystyrene beads, or polyurethane foam. The process is carried out from outside the property by drilling small holes in the mortar joints, which are filled and made good after installation.

How It Works

Eligibility Check

A surveyor confirms your home has cavity walls (typically built after 1920), checks the cavity width, and assesses the condition of the brickwork and any potential issues.

Drill Injection Holes

Small holes (around 22mm diameter) are drilled into the external mortar joints at regular intervals across the wall surface.

Inject Insulation

Insulation material is pumped through the holes under pressure, filling the cavity evenly from bottom to top.

Make Good

The drill holes are sealed with matching mortar. The entire process typically takes two to three hours with no disruption inside the home.

Is It Right for My Home?

Cavity wall insulation is suitable for homes built from approximately 1920 onwards that have unfilled cavity walls. The cavity must be at least 50mm wide. Properties with severe exposure to wind-driven rain, damaged brickwork, or very narrow cavities may not be suitable. A professional survey will confirm eligibility. Homes with solid walls (typically pre-1920) will need external or internal wall insulation instead.

Key Benefits

Cut Heating Bills

Save up to £310 per year by preventing heat from escaping through your walls, reducing the amount of energy needed to keep your home warm.

Quick Installation

Most cavity wall insulation jobs are completed in just two to three hours, with all work carried out from outside — no internal disruption.

Even Room Temperatures

Insulated walls reduce cold spots and draughts, creating a more comfortable and consistent temperature throughout your home.

Reduce Condensation

Warmer internal wall surfaces help reduce condensation and the associated risk of damp and mould growth.

Lower Carbon Emissions

Reducing your gas consumption directly cuts your household carbon footprint, contributing to the UK's climate goals.

Improve EPC Rating

Cavity wall insulation can improve your Energy Performance Certificate by one or more bands, increasing your home's value and saleability.

Cost Breakdown

Our partner network means you'll typically pay less than these averages.

Property Type	Typical Cost	Annual Saving	Payback
Detached	£600 – £700	£310	2–3 years
Semi-Detached	£450 – £550	£215	2–3 years
Terraced	£400 – £475	£160	2–3 years
Bungalow	£400 – £500	£175	2–3 years

Government Grants Available

ECO4

The ECO4 scheme provides fully funded cavity wall insulation for eligible low-income households and those receiving qualifying benefits such as Universal Credit or Pension Credit.

Check Eligibility →

Warm Homes Plan

The Warm Homes Plan offers grants towards cavity wall insulation for fuel-poor households, helping to reduce energy bills and improve home warmth.