Cavity walls are one of the biggest sources of heat loss in UK homes. If the space between the inner and outer walls is not insulated, warm air escapes through the walls far more quickly, making the home difficult to heat and much more expensive to run.

Under the ECO4 scheme, eligible households can receive free cavity wall insulation, which is one of the most effective upgrades for boosting energy efficiency, improving warmth, and lowering heating bills.

How cavity wall insulation works

Most homes built after the 1920s have cavity walls — two layers of brick with a gap in between. This cavity allows heat to escape unless it is filled with proper insulation.

During installation, specially designed insulation beads are blown into the cavity through small drilled holes in the external wall. These beads lock together, forming a solid thermal barrier that prevents heat loss.

Cavity wall insulation under ECO4

ECO4 funds cavity wall insulation when:

• The property has suitable cavity walls
• The cavity is empty or poorly insulated
• The home has a low EPC rating (D–G)
• The upgrade forms part of the whole-house plan to improve efficiency

A qualified surveyor will inspect the walls to confirm they are suitable, check for signs of damp, and make sure the property’s structure allows for safe installation.

Benefits of cavity wall insulation

• Significantly reduced heat loss
• Lower annual heating bills
• Warmer rooms and fewer cold spots
• Improved EPC rating
• Faster heat-up times for the home
• Long-lasting, maintenance-free insulation

Cavity wall insulation delivers some of the biggest improvements in overall energy efficiency, especially when combined with loft insulation or internal wall insulation.

25-year guarantee

All cavity wall insulation installed under ECO4 comes with a 25-year guarantee, giving you long-term protection and peace of mind.

Installation quality

All work is completed by certified, TrustMark-accredited installers, ensuring safe installation, structural protection, and compliance with government standards.

For eligible households, cavity wall insulation is one of the quickest, most cost-effective upgrades — and can transform the warmth and efficiency of your home for decades.