If you’re considering cavity wall insulation, the first thing you need to know is whether your home actually has cavity walls. Not all properties do, and insulating a solid wall as though it were a cavity wall isn’t possible.
The good news is there are a few straightforward ways to check without needing a professional. Here’s how.
What Is a Cavity Wall?
A cavity wall is made up of two separate layers, an outer wall and an inner wall, with a gap (the cavity) between them. The outer layer is usually brick, and the inner layer is typically brick or concrete block. The cavity between them is usually 50mm to 100mm wide.
This gap was originally designed to stop rainwater reaching the inside of your home. Rain can penetrate the outer layer of brickwork, but the cavity prevents it from crossing to the inner wall. It also provides a space that can be filled with insulation to reduce heat loss.
Check Your Brick Pattern
This is the quickest way to check if you have an exposed brick exterior.
Cavity walls: If all the bricks are laid lengthways in a uniform, stretcher bond pattern (you only see the long rectangular faces), your home almost certainly has cavity walls. This is the most common pattern on UK homes built from the 1930s onwards.
Solid walls: If you can see a mix of long bricks and shorter square ends (called headers) alternating in the pattern, your walls are likely solid. This is known as Flemish bond or English bond, and is typical of older Victorian and Edwardian properties.
If your external walls are rendered, pebble-dashed, or clad in timber, you won’t be able to see the brick pattern. In that case, the wall thickness method below is more reliable.
Measure Your Wall Thickness
You can do this at any open window or external doorway. Measure from the inside surface of the wall to the outside surface.
Cavity walls are typically 260mm to 350mm thick. The two layers of brick or block plus the cavity between them add up to a wider overall wall.
Solid walls are usually under 260mm. A single-brick solid wall is around 220mm thick.
If your walls are thicker than 350mm, your home may have been built with a wider cavity, or may have already had insulation installed. A professional survey can confirm exactly what’s inside the wall.
Check Your Property Age
The age of your home is a useful indicator, though not a guarantee.
Built after the 1930s: Almost certainly cavity walls. Cavity wall construction became standard practice across the UK from the late 1920s onwards.
Built between 1920 and 1935: Likely cavity walls, but some properties from this transition period were still built with solid walls. Worth checking with the brick pattern or wall thickness method.
Built before 1920: Most likely solid walls. Victorian and Edwardian homes were typically built with solid brick construction. However, some properties from this era do have cavities, particularly in certain regions, so it’s not a definitive rule.
Built after the 1990s: Almost certainly has cavity walls, and they may already have insulation installed from when the property was built. Building Regulations from the 1990s onwards generally required insulation to be included during construction.
What About Properties in Cheshire and the North West?
Across our service area in Cheshire, Greater Manchester, Shropshire and Staffordshire, the housing stock is varied. Semi-detached and terraced homes in towns like Nantwich, Crewe, Stockport and Warrington, many built from the 1930s through to the 1970s, are typically cavity wall construction and are good candidates for insulation.
Older properties in areas like Chester’s city centre, parts of Shrewsbury, and some of Manchester’s Victorian terraces are more likely to have solid walls. Properties in rural Cheshire and Shropshire can vary depending on when and how they were built.
If you’re unsure, that’s what our free assessment is for.
Still Not Sure? Book a Free Assessment
The methods above will give you a good indication, but the only way to know for certain what’s inside your walls is a professional inspection. During our free cavity wall assessment, we use a borescope camera to look directly into the cavity through a small drilled test hole. This confirms whether you have cavity walls, whether the cavity is clear or already filled, and whether your property is suitable for insulation.
The assessment is free, takes around 30 minutes, and there’s no obligation.
Book a free cavity wall assessment → | Call 01270 814145
Frequently Asked Questions
How can I tell if I have cavity walls without drilling?
Check the external brick pattern (uniform lengthways bricks suggest cavity walls) and measure the wall thickness at a window or doorway (260-350mm indicates cavity walls). Your property’s age is also a useful guide: most UK homes built after the 1930s have cavity walls.
Can I check if my cavity walls are already insulated?
Sometimes you can spot small circular marks in the mortar joints on the outside of your home, which indicate drill holes from a previous insulation installation. However, the only reliable way to confirm is a borescope inspection, which looks directly into the cavity.
My walls are rendered. How do I check?
If you can’t see the brick pattern, measure the wall thickness at an open window or doorway. Cavity walls are typically 260-350mm thick. If you’re still unsure, a professional assessment will confirm it.
Do all cavity walls need insulating?
Not necessarily. Some properties aren’t suitable due to narrow cavities, damaged brickwork, high exposure to wind-driven rain, or existing damp issues. We always assess your property before recommending any work.