Free Cavity Wall Insulation 2026: How to Apply Under ECO4

Free cavity wall insulation is available to eligible UK households in 2026 through the ECO4 scheme. If your home was built between roughly 1920 and 2000 and has unfilled cavity walls, and you receive qualifying benefits or have a poor EPC rating, you could have cavity wall insulation installed at no cost.

The ECO4 scheme ends on 31 December 2026, so eligible households should check their eligibility now.

What is cavity wall insulation and why does it matter?

Cavity wall insulation involves filling the gap (or "cavity") between the inner and outer walls of a property with insulating material — typically mineral wool, polystyrene beads, or polyurethane foam. Once filled, the wall is much better at retaining heat.

Many homes built in the UK between the 1920s and early 2000s were constructed with cavity walls that were not filled at the time of building. Uninsulated cavity walls can account for up to 35% of a home's heat loss, meaning a significant portion of your heating bill may be escaping through your walls.

Cavity wall insulation typically:

• Reduces heating bills by hundreds of pounds per year in homes with high heat loss
• Improves EPC ratings — often by a full grade or more
• Makes the home more comfortable, with fewer cold spots
• Reduces carbon emissions

Is free cavity wall insulation available in 2026?

Yes. Through ECO4, eligible households can receive cavity wall insulation at no cost. The scheme funds the full cost of materials and installation — there is nothing to pay.

ECO4 is still accepting applications in 2026, but the scheme ends on 31 December 2026. After that date, free cavity wall insulation for eligible households will need to be accessed through the Warm Homes Local Grant, delivered by local councils — a different and potentially slower process.

Does my property have cavity walls?

Not all properties have cavity walls. Here is a general guide:

If you are unsure whether your walls are solid or cavity, an approved installer can check this for free as part of a property assessment. They can also use specialist equipment to confirm whether an existing cavity is already filled.

Who qualifies for free cavity wall insulation under ECO4?

Eligibility for ECO4 — and therefore for free cavity wall insulation — is based on two routes:

Benefits route: You or someone in your household receives a qualifying benefit:

• Universal Credit
• Pension Credit
• Child Benefit
• Income Support
• Income-based Jobseeker's Allowance (JSA)
• Income-related Employment and Support Allowance (ESA)
• Housing Benefit
• Working Tax Credit or Child Tax Credit

Property route: Your home has an EPC rating of D, E, F or G, even if you don't receive qualifying benefits.

Both homeowners and private renters are eligible. Social housing tenants (council or housing association) should speak to their landlord.

How to apply for free cavity wall insulation under ECO4

The process is simple:

1. Check eligibility — Use our free online checker to confirm your initial eligibility in about 2 minutes.
2. Book a property assessment — An approved installer will visit your property to assess your walls and confirm which measures are available and suitable.
3. Installation — If approved, cavity wall insulation is installed by trained technicians, typically in a single day. Holes are drilled in the outer wall, the insulating material is injected, and the holes are sealed and made good.

You do not need to contact your energy supplier or any government body. Approved installers manage the ECO4 application process on your behalf.

What does cavity wall insulation installation involve?

The installation process is minimally disruptive:

• Technicians drill small holes (around 22mm) in the outer wall of your property, typically at regular intervals
• Insulating material is injected through the holes to fill the cavity
• The holes are sealed with matching mortar
• Most installations take between four and eight hours for an average semi-detached house
• You can remain in your home throughout
• There is no significant mess inside the property

After installation, your walls will look the same from the outside, with only small mortar patches visible where the holes were drilled.

How much could I save?

The savings from cavity wall insulation depend on your home's size, construction, and current heating system. According to energy industry estimates:

• A semi-detached home could save around £200–£350 per year in heating costs
• A detached house could save £400–£600 per year
• A mid-terrace house could save around £150–£250 per year

For ECO4 eligible households, these savings come at no upfront cost, making the return on investment immediate.

Frequently asked questions

Can I get cavity wall insulation if I'm a private renter? Yes, if you qualify under ECO4 (through benefits or poor EPC rating). Your landlord will need to give consent for the work to be carried out, but as the work is free and improves the property, most landlords agree.

What if my cavity is already partially filled? In some cases, older cavity wall insulation may have deteriorated or only partially filled the cavity. An installer can assess this and advise on whether re-filling is appropriate.

Is cavity wall insulation covered under guarantee? Cavity wall insulation installed under ECO4 must be covered by a recognised guarantee scheme. Your installer will provide details of the applicable guarantee.

What if my walls are solid, not cavity? Solid walls can be insulated using external or internal solid wall insulation, which is a different and more complex (and expensive) process. ECO4 can fund solid wall insulation for eligible households in some cases. An installer will advise.

How long does the ECO4 application take? From initial enquiry to completed installation, the process typically takes four to ten weeks depending on installer capacity in your area. With the December 2026 deadline approaching, it is advisable to start the process as soon as possible.