Tech guide: Is cavity wall insulation right for your home?

Cavity wall insulation is one of the most effective ways to improve your home’s energy efficiency, helping to reduce energy bills and create a warmer, more comfortable living space. But it’s not suitable for every home, and if installed incorrectly, it can lead to serious damp and ventilation issues.

Before taking the plunge, here’s what you need to know:

How does cavity wall insulation work?

Many homes built after 1920 have cavity walls, with a gap between the inner and outer layers. Insulating this space by injecting mineral wool, polystyrene beads, or polyurethane foam can cut heat loss by up to a third, keeping more warmth inside.

But: This work must be carried out by a qualified professional, as poor installation or unsuitable conditions can cause damp problems.

Is my home suitable?

Cavity wall insulation isn’t a one-size-fits-all solution. Some homes are more at risk of damp or poor performance. Key considerations include:

• Age of the property – Homes built before 1920 typically have solid walls and need a different insulation approach.
• Exposure to weather – If your walls are exposed to heavy wind-driven rain or have had past damp issues, cavity insulation may trap moisture, causing mould.
• Cavity width – If the cavity is too narrow, insulation may not be effective.

A professional whole house energy efficiency assessment is essential to determine whether cavity wall insulation is the right solution.

Costs and savings

The cost of cavity wall insulation varies based on your home’s size and type. Estimates from Which? suggest:*

• Detached house – £4,600 installation, up to £370 annual savings
• Semi-detached house – £2,800 installation, up to £230 annual savings
• Mid-terrace house – £2,300 installation, up to £160 annual savings
• Bungalow – £2,500 installation, up to £180 annual savings
• Flat – £950 installation, up to £100 annual savings

Many homeowners recover their costs within five years, making it a worthwhile investment when done correctly.

*Prices from 2024, are subject to inflation, and may vary depending on region, and type of insulation.

The risks of single retrofit measures

Cavity wall insulation is not a standalone solution. Adding insulation without considering ventilation, moisture control, and heating systems can lead to serious unintended consequences, such as:

• Damp and mould caused by trapped moisture in walls.
• Poor ventilation, leading to condensation and unhealthy indoor air quality.
• Overheating in summer if insulation is not paired with proper shading and ventilation strategies.

To avoid expensive mistakes, insulation should be part of a whole-house retrofit plan that considers how all elements of your home work together.

Plan your insulation properly

At Cosy Homes Oxfordshire, we take a whole-house approach to insulation, ensuring every improvement is designed to work with your home’s unique needs for maximum comfort, energy savings, and long-term value.

Get in touch with our team on 0330 223 2742 or send us a message to book a home energy efficiency assessment and receive a tailored Whole House Plan—helping you make the right refurbishment decisions for a warmer, healthier, and more efficient home.