How to Tell If Your Lancashire Home Has Cavity Wall Insulation

Around 35% of eligible homes in Lancashire still do not have cavity wall insulation, despite it being one of the most cost-effective energy-saving measures available. Filling the cavity in a typical 3-bed semi costs £800-£2,500 privately but is often available for free or heavily subsidised through government energy efficiency schemes funding. It saves an average of £185-£290 per year on heating bills. If you are not sure whether your Lancashire home has cavity walls or whether they have already been filled, here are five reliable ways to find out.

Cavity wall construction became standard in most of England from the 1930s onwards, with the cavity (a gap between the inner and outer walls) designed to prevent damp penetration. Homes built between 1930 and 1990 in Lancashire almost certainly have cavity walls but may or may not have had them filled with insulation. Homes built after 1990 should have been insulated during construction, though this is not guaranteed. Homes built before 1920 are more likely to have solid walls with no cavity at all.

Method 1: Measure the Wall Thickness

The simplest check is to measure the thickness of an external wall at a door or window opening. Open a window or door and measure the total wall thickness from the inside surface to the outside surface:

• Less than 260mm (about 10 inches): Almost certainly a solid wall with no cavity. Common in pre-1920 Lancashire terraces.
• 260-300mm (about 10-12 inches): Likely a cavity wall. The cavity itself is typically 50-75mm wide.
• Over 300mm: Could be a wider cavity, a solid stone wall, or a cavity wall that has already been insulated (filled cavities make the wall feel slightly thicker due to the insulation material).

In Lancashire’s stone-built areas (Rossendale, Pendle, Ribble Valley), thick stone walls can be 400-600mm and may look like they have a cavity but actually do not. Stone walls need specialist assessment.

Method 2: Look at the Brick Pattern

If your home has exposed brickwork (not rendered or pebble-dashed), the brick-laying pattern tells you a lot:

Cavity wall pattern: All bricks are laid lengthways (the long face showing). This is called stretcher bond, and it means the outer wall is a single layer of bricks with a cavity behind.

Solid wall pattern: A mix of long bricks (stretchers) and short bricks (headers, showing the end of the brick). This is Flemish bond or English bond, and it means the bricks are interlocked through the full thickness of the wall with no cavity.

Many Lancashire terraces from the Victorian and Edwardian era show the solid wall pattern clearly. If yours shows the stretcher-only pattern, you likely have a cavity wall.

Method 3: Check Your EPC

Your Energy Performance Certificate (EPC) contains information about your wall construction and insulation status. You can look up your EPC for free on the government’s EPC register using your postcode.

Look for the “Walls” section in the EPC details. It will state something like:

• “Cavity wall, filled” – you already have cavity wall insulation
• “Cavity wall, unfilled” or “Cavity wall, as built” – you have cavity walls that have NOT been insulated
• “Solid brick, no insulation” – you have solid walls, not cavity
• “System built” or “Timber frame” – your construction type is different (cavity wall insulation does not apply)

Be aware that EPCs are sometimes inaccurate, particularly for older properties or where the assessor could not verify the wall construction. If the EPC says “assumed unfilled” or similar, the assessor was making a best guess. A professional cavity wall survey is more reliable.

Method 4: Look for Drill Holes

If your cavity walls have been filled, there should be evidence of the injection process on the outside of the building. Cavity wall insulation is pumped into the wall through small holes (typically 22mm diameter) drilled through the outer wall at regular intervals.

Look for a pattern of small, filled-in holes on the external walls, usually about 1 metre apart horizontally and at regular vertical intervals. The holes are filled with mortar after injection, so they appear as slightly different-coloured or textured spots on the brickwork. They are most visible on red brick and can be harder to spot on rendered or pebble-dashed walls.

If you can see these holes, your cavity walls have almost certainly been insulated. If there are no holes visible anywhere on the external walls, the cavity is likely unfilled.

Method 5: Get a Professional Borescope Inspection

The definitive test is to have a professional drill a small hole in the external wall and insert a borescope (a tiny camera on a flexible cable) into the cavity to see whether it is empty or filled. This takes about 10 minutes, creates a hole the size of a pencil (which is filled afterwards), and gives a clear answer.

Many cavity wall insulation companies in Lancashire offer free borescope inspections as part of their survey. If you are considering getting your cavity filled, the surveyor will do this check as standard. It is also useful if you suspect a previous insulation job has deteriorated (old foam or bead insulation can settle or degrade over time).

What If Your Cavity Is Unfilled?

If you discover your Lancashire home has unfilled cavity walls, getting them insulated is one of the best value energy improvements you can make:

• Cost if paying privately: £800-£2,500 depending on property size
• government energy efficiency schemes funding: Potentially free if you receive qualifying benefits and your home is EPC D or below
• government insulation scheme: Potentially free or subsidised if your home is in Council Tax band A-D
• Annual saving: £185-£290 per year on heating bills
• Payback period (if paying privately): 3-9 years
• Installation time: 2-4 hours for a standard property

The process is straightforward: an installer drills small holes in the external wall at regular intervals, pumps insulation material (usually mineral wool, polystyrene beads or foam) into the cavity, and fills the holes. There is minimal disruption and no internal work required.

When Cavity Wall Insulation Is Not Suitable

Not every cavity wall should be filled. There are circumstances where cavity wall insulation can cause problems:

• Exposed locations: Homes on exposed hillsides in the Pennines or along the Fylde coast may experience wind-driven rain penetrating through filled cavities. A specialist assessment is essential in these locations.
• Narrow cavities: Cavities less than 50mm wide may not fill properly or may bridge moisture across to the inner wall.
• Existing damp problems: If there are existing damp or moisture issues in the walls, these should be resolved before cavity insulation is installed.
• Damaged or missing wall ties: Corroded wall ties can mean the cavity is not structurally suitable for insulation without remedial work first.

A reputable installer will assess all of these factors during their survey. Our guide on dealing with damp and condensation in Manchester terraced houses covers moisture issues in more detail.

Can cavity wall insulation cause damp?

In most situations, properly installed cavity wall insulation does not cause damp. However, in exposed locations where wind-driven rain is severe, incorrectly installed insulation can act as a bridge for moisture. This is why a thorough pre-installation survey is essential. If your home is in an exposed position, the surveyor should assess whether cavity wall insulation is appropriate or whether alternative methods are better.

My home has been rendered – can I still check for cavity insulation?

Yes. You cannot see the brick pattern or drill holes through render, but you can still measure wall thickness at windows and doors. The borescope inspection method works through render too – the surveyor drills through the render and brick into the cavity. An EPC check is also a good starting point for rendered properties.

How long does cavity wall insulation last?

Modern cavity wall insulation (mineral wool or EPS beads) is expected to last the lifetime of the building – typically 25+ years. Older urea formaldehyde foam (used in the 1970s-80s) can shrink and degrade over time, and some homes have had this old foam extracted and replaced with modern materials. If your home was insulated 30-40 years ago, a borescope check can confirm whether the insulation is still performing.