If your home feels draughty or your heating bills seem higher than they should be, your walls may be responsible. In an uninsulated property, about 25–35% of heat can escape straight through external walls, making your heating work overtime and costing you more than necessary.
If your home was built after the 1920s, chances are it features cavity walls that are perfect candidates for insulation.
Cavity wall insulation is one of the simplest, quickest, and most cost-effective ways to make your home warmer, reduce energy waste and bring down annual bills. Unlike external wall insulation, the process involves filling the gap or cavity between your home’s inner and outer walls with an insulating material, effectively slowing the transfer of heat.
Cavity wall insulation costs
Average installation costs per property type
The cost of cavity wall insulation in the UK varies depending on property size, insulation material, and installer rates. On average, most homeowners can expect to pay:
- Detached house: £2,700–£4,600.
- Semi-detached house: £1,500–£2,700.
- Terraced house: £950–£1,800.
- Flat or maisonette: £950–£1,400.
These prices generally include all materials, labour, and a guarantee (commonly 20–25 years). The price may be marginally higher if any old insulation needs removing or if your property is in London or the South East, where labour is more expensive.
DIY vs professional installation costs
DIY cavity wall insulation isn’t generally recommended. Professional installers use specialised equipment to drill small holes in external brickwork and inject insulation throughout the cavity under controlled pressure. Doing this yourself can result in cold spots, damp problems or incomplete installation, and you could end up having to pay a professional to sort it out.
Professional installation costs usually range from £13 to £30 per m², depending on the insulation material. While that’s higher than DIY kit costs, you benefit from total coverage, professional guarantees, and compliance with building regulations.
Payback period and long-term savings
A properly insulated home can save anywhere from £110 a year (flats) to £405 a year (detached homes) on heating. With a typical lifespan of 25 years or longer, payback periods are often between three and 10 years, one of the fastest for any insulation upgrade. If you qualify for grants, the payback starts immediately, and your home is warmer from day one.
Types of cavity wall insulation materials
Mineral wool/glass wool
Mineral wool is blown into the cavity, providing thermal and acoustic benefits. It is fire resistant, breathable, and widely used across the UK, especially for older homes.
Polystyrene beads
Polystyrene beads (sometimes coated with adhesive) are injected into the cavity, filling gaps thoroughly and working well around structural obstructions. They deliver excellent thermal efficiency, are lightweight, moisture-resistant, and ideal for exposed or complex wall structures.
Urea formaldehyde foam (older method)
Although it was common decades ago, foam insulation is rarely installed nowadays due to shrinkage and moisture issues. If your home has historic foam insulation, professional checks are advisable.
Which insulation material is best?
For most homes, mineral wool and polystyrene beads are the top choices. Mineral wool is cost-effective and durable; beads offer better moisture resistance for exposed sites. Your installer will advise the best fit for your property, taking into account cavity size, exposure, and budget.
How cavity wall insulation is installed
Professional installation process (step-by-step)
- Survey: An expert checks the suitability of your walls (cavity width, existing insulation, exposure).
- Drilling holes: Small holes are drilled in exterior brickwork at intervals.
- Injecting insulation: Chosen material is pressure-blown or injected to fill the cavity evenly.
- Sealing holes: Mortar is used to refill the holes, blending with the existing brickwork.
- Final check: The installers confirm that the cavity is fully insulated and issue a guarantee certificate.
How long does it take?
For the typical family home, installation is completed in two to four hours, with minimal disruption since all work is performed from outside. Larger properties may take a full day. Once it’s complete, you can usually carry on living as normal, only in a warmer home.
Can you DIY cavity wall insulation?
DIY kits exist but aren’t recommended due to technical demands and potential risks. Only professionals have the right tools to ensure every part of the cavity is filled and to offer a warranty. If you’re planning to sell or rent your home, professional certification is vital.
People also ask
How do I know if my house has cavity wall insulation?
Most homes built from the 1920s to the 1990s feature cavity walls. A uniform brickwork pattern is one clue; for confirmation, check for filled drill holes at intervals on exterior walls or book a borescope inspection.
What is the difference between cavity and solid wall insulation?
Cavity wall insulation fills the gap between two walls; solid wall insulation is added inside or outside homes without a cavity (usually older properties). Solid wall solutions are typically more expensive and disruptive.
Is cavity wall insulation worth it?
Absolutely. It is one of the lowest-cost energy upgrades, pays back quickly, and often makes homes cosier, quieter, and more valuable on the market. It can also help you meet the legally required Minimum Energy Efficiency Standards as a landlord.
Does cavity wall insulation make your house warmer?
By dramatically reducing lost heat, cavity wall insulation keeps rooms comfortable in winter and cooler in summer. Fewer cold spots and draughts are common benefits.
How much does cavity wall insulation cost for a 3-bed house?
For a typical 3-bed semi, you could expect costs between £1,500 and £2,700, depending on location and wall size.
Is cavity wall insulation free?
Many homeowners qualify for support under government grants like ECO4 or the Great British Insulation Scheme, especially if the property has a low EPC rating or occupants receive certain benefits. Professional installers such as Eco Insulation can check eligibility and arrange funded installation.
Cavity wall insulation remains a quick, affordable, and high-impact way to cut bills and improve home comfort.