The Difference Between Cavity Wall and Solid Wall Insulation

When it comes to keeping your home warm and energy-efficient, wall insulation plays a crucial role. But what’s the difference between cavity wall insulation and solid wall insulation? And which one might your home need?

At Warmify, we’re here to explain the difference—and show you how to access free insulation through trusted schemes.

What is Cavity Wall Insulation?

Many homes built after the 1920s have cavity walls—two layers of brick with a gap (or “cavity”) between them.

Cavity wall insulation fills this gap with insulating material, stopping heat from escaping and making your home more energy-efficient.

Ideal for homes built after the 1920s.
Quick and affordable to install—and free if you qualify.

What is Solid Wall Insulation?

Older homes (often pre-1920s) typically have solid walls, with no gap between layers. Insulating these walls requires either:

• Internal solid wall insulation – boards fitted to the inside of walls.
• External solid wall insulation – insulating material added to the outside, finished with render or cladding.

Ideal for older, solid-walled properties.
Improves energy efficiency and reduces draughts.

How to Tell Which Walls You Have

• Check the age of your home – Pre-1920s homes are likely solid wall; post-1920s are often cavity.
• Look at the brickwork – Cavity walls usually have regular brick patterns; solid walls often have bricks laid lengthwise.
• Check your EPC – It will state your wall type.

Not sure? Don’t worry.

Use our quick eligibility checker to see if you qualify for a free survey and advice.
Contact us for help identifying your wall type and what upgrades suit your home.

Why Insulate Your Walls?

• Lower energy bills – Proper insulation can cut heating costs by up to 35%.
• Improved comfort – Warmer, draught-free rooms.
• Better EPC rating – A more energy-efficient home can boost property value.
• No upfront cost – If you’re eligible, insulation is fully funded.
  
  

Warmify Makes It Easy

• We check your eligibility for funding.
• We arrange a free home survey.
• We recommend cavity or solid wall insulation based on your home.
• We manage the installation—at no cost to you.
  
  

Take the First Step

Wall insulation can make a big difference to your home’s comfort and energy bills. Let Warmify help you find out what’s right for your home.