Cavity wall insulation costs between £250 and £2,500 in the UK, depending on your house type and the material used. A mid-terrace home can be insulated for as little as £250, while a large detached property typically costs £600-£2,500. Installation takes just 2-3 hours, and annual energy savings of £180-£395 mean most homeowners recoup the cost within 3-5 years.
We have compared installer pricing across all UK house types and insulation materials to give you an accurate cost breakdown for 2026. All prices include materials, labour, and the standard 25-year CIGA guarantee. We also cover who qualifies for free cavity wall insulation through government grants.
- A 3-bed semi costs £350-£1,000 for cavity wall insulation - installation takes 2-3 hours through small drill holes in the outer wall, with no internal disruption
- Detached homes save £180-£395 per year on heating bills - payback period is 3-7 years depending on property size, even without government grant funding
- Mineral wool is the most common material at £250-£700 - it is fire-resistant, moisture-permeable, and comes with a 25-year CIGA guarantee as standard
- Free insulation is available through ECO4 and GBIS grants - households on qualifying benefits or in EPC band D-G properties can get fully funded installation
- Not all homes are suitable for cavity wall insulation - properties with narrow cavities (under 50mm), severe rain exposure, or solid walls need an alternative approach
How Much Does Cavity Wall Insulation Cost?
Cavity wall insulation costs vary primarily by house type, because larger homes have more wall area to fill. A mid-terrace property has the smallest external wall area and costs the least, while a detached home with four exposed walls costs the most. Here is a breakdown by house type for 2026.
| House Type | Cost Range | Annual Saving | Payback Period |
|---|---|---|---|
| Mid-terrace | £250-£700 | £90-£175 | 2-4 years |
| End-terrace | £300-£900 | £130-£260 | 2-4 years |
| Semi-detached | £350-£1,000 | £150-£310 | 2-4 years |
| Detached | £600-£2,500 | £180-£395 | 3-7 years |
| Bungalow | £350-£900 | £120-£240 | 2-4 years |
These prices include materials, labour, and the standard CIGA (Cavity Insulation Guarantee Agency) guarantee. Prices can vary by 10-20% depending on your region, with London and the South East typically at the higher end.
Cost by Insulation Material
Three main materials are used for cavity wall insulation in the UK, each with different properties and price points. Your installer will recommend the best option based on your wall construction, cavity width, and local weather exposure.
| Material | Cost (3-bed semi) | Thermal Performance | Best For |
|---|---|---|---|
| Mineral wool | £350-£700 | Good | Standard cavities (50mm+), most common choice |
| Polystyrene beads | £400-£900 | Good | Irregular cavities, rubble-filled walls |
| Polyurethane foam | £500-£1,200 | Excellent | Narrow cavities, maximum thermal performance |
Mineral wool (also called rock wool or glass wool) is the industry standard and suits most properties. Polystyrene beads flow around obstructions better than wool, making them useful for walls with rubble or debris in the cavity. Polyurethane foam offers the best thermal performance per millimetre but costs more and cannot be easily removed if problems arise.
How Cavity Wall Insulation Works
A registered installer drills small holes (around 22mm diameter) into the mortar joints of your outer wall at regular intervals. Insulation material is then injected through the holes using specialist equipment, filling the cavity between the inner and outer walls. The holes are sealed and colour-matched to the existing mortar.
The entire process takes 2-3 hours for a typical semi-detached home. There is no internal disruption, no need to move furniture, and you can stay in the property throughout. The injection holes are virtually invisible once sealed.
Before installation, the surveyor checks your cavity width (needs to be at least 50mm), wall condition, and exposure level. Properties in exposed locations with heavy driving rain may not be suitable, as trapped moisture can cause damp problems. A reputable installer will always complete this survey before quoting.
Is Cavity Wall Insulation Worth It?
For most eligible homes, cavity wall insulation is one of the best energy upgrades available. The combination of low cost, fast installation, and significant energy savings makes it hard to beat on pure return on investment.
A semi-detached homeowner paying £500 for cavity wall insulation and saving £230 per year will recoup the cost in just over 2 years. Over a 25-year guarantee period, that is a total saving of over £5,000 – a 10x return on investment.
Beyond bill savings, cavity wall insulation improves your EPC rating (typically by 1-2 bands), reduces condensation on cold internal walls, and makes your home noticeably warmer and more comfortable. If you are planning to sell, a higher EPC rating is increasingly important to buyers and can support a higher asking price.
Who Cannot Get Cavity Wall Insulation?
Not every home is suitable for cavity wall insulation. Around 30% of UK homes have solid walls with no cavity, and others may have cavities that are already filled or too narrow. Understanding whether your home qualifies is the first step before requesting quotes.
Your home is unlikely to be suitable if:
- It was built before the 1920s (most pre-1920 homes have solid walls with no cavity)
- The cavity is narrower than 50mm
- The cavity has already been filled
- Your home is in a severely exposed location with persistent driving rain
- There is existing damp or structural damage to the walls
If your home has solid walls, external wall insulation or internal wall insulation are the alternatives. Both cost significantly more but can still be partially or fully funded through government grants.
Cavity Wall Insulation Risks and Problems
While cavity wall insulation is safe and effective for most properties, problems can occur when it is installed in unsuitable homes. The most common issue is damp penetration in properties with high rain exposure. Insulation material can bridge the cavity and allow moisture to track through to the inner wall.
Other potential issues include incomplete filling (leaving cold spots), settling of bead insulation over time, and foam insulation that cannot be easily removed if problems develop. These risks are minimised by using a CIGA-registered installer who carries out a proper pre-installation survey.
If you experience damp problems after cavity wall insulation, contact your installer immediately. CIGA guarantees cover extraction and remediation for 25 years. Do not ignore signs of damp – early intervention prevents costly damage.
The CIGA guarantee is your main protection. It covers the cost of extracting and replacing insulation if problems arise within 25 years. Always check that your installer is CIGA-registered and that a guarantee certificate is issued after completion.
How to Get Cavity Wall Insulation Quotes
Getting competitive quotes is straightforward, but a few steps will help you avoid overpaying or choosing the wrong installer. Always get at least three quotes from different companies to compare pricing and recommendations.
Check that every installer is TrustMark-registered and a member of CIGA. Ask what material they recommend and why, whether the price includes the CIGA guarantee, and how long the installation will take. A good installer will always complete a physical survey before quoting and will explain any risks specific to your property.
Government insulation grants through ECO4 and GBIS can cover the full cost for eligible households. Even if you do not qualify for free insulation, you may be able to access discounted installation through energy company obligations. For a broader view of all insulation options and costs, see our home insulation cost hub.
