What is cavity wall insulation and how does it work?

Cavity wall insulation is a method used to reduce heat loss and energy consumption in buildings by filling the gap between the external and internal walls with insulating materials. This gap, known as a cavity, is typically found in homes built between the 1920s and 1980s in the UK. Insulating this space allows homeowners to maintain a more stable indoor temperature year-round, saving energy and reducing energy bills.

How it Works

The process involves drilling small holes at regular intervals in the external walls and then injecting insulating materials into the cavity from the outside. Common materials include mineral wool, Expanded Polystyrene (EPS) beads combined with a binding agent, and Urea Formaldehyde (UF) foam insulation. To ensure effectiveness, the insulation must fill all parts of the cavity. This method helps reduce the U-value of the walls, improving their thermal performance.

Real-World Applications and Examples

In the UK, millions of homes (approximately 5 million) can benefit from cavity wall insulation, especially those built within the specified period. UK homeowners who have installed cavity wall insulation often report significant reductions in heating costs and a more comfortable living environment.

Key Pros and Cons

Pros

• Energy Savings: Reduces heat loss, leading to lower energy bills.
• Cost-Effective: Compared to other insulation types, it's relatively inexpensive.
• Eligibility for Grants: Many UK homeowners may qualify for free installation through government-backed schemes.
• Maintenance of Wall Integrity: Helps preserve the structural integrity by preventing moisture from entering the cavity, although exceptions exist.

Cons

• Potential Damp Issues: In rare cases, especially in exposed locations or where the external walls are in poor condition, filling the cavity can lead to damp problems.
• Installation Challenges: Requires access to all parts of the external wall, which can be difficult for some properties.
• Cost of Incorrect Installation: If not done properly, it can lead to costly repairs.

Practical Advice

• Assessment: Before installation, ensure that your walls are suitable for cavity wall insulation. A boroscope inspection can determine this.
• Quality Installation: Ensure that the installer is reputable and covered by a guarantee such as the Cavity Insulation Guarantee Agency (CIGA).
• Address Existing Damp Issues: If your home has existing damp problems, rectify these before installing insulation.

Common Mistakes and Solutions

• Insufficient Filling: Ensure the insulation fills all parts of the cavity to avoid gaps and ineffective insulation.
• Ignoring Damp Conditions: Always address damp issues before installing insulation to prevent worsening the problem.
• Poor Access Management: Plan for adequate access to all external walls during installation.