If you have been putting off applying for eco4, the clock is now genuinely running out. The scheme that has funded free and subsidised wall insulation for hundreds of thousands of UK households is closing its obligation period on 31 December 2026, and after that date there is no confirmed successor scheme in the same form.

What Eco4 Actually Is

Eco4 is the fourth version of the Energy Company Obligation, a government backed scheme that requires energy suppliers to fund energy efficiency measures in eligible homes. It is administered by Ofgem on behalf of the Department for Energy Security and Net Zero, and it exists to tackle fuel poverty while cutting household energy bills.

Unlike a simple grant, eco4 takes what is called a whole house approach. Instead of funding a single measure in isolation, suppliers are encouraged to install combinations of improvements together, cavity wall insulation alongside loft insulation, for example, because the combined effect on a home’s energy performance is greater than any single measure on its own.

Who Actually Qualifies for Eco4

Eligibility is based primarily on receiving certain means tested benefits, such as Universal Credit, Pension Credit, or Income Support. Alongside that, your property typically needs an EPC rating of E, F, or G, since the scheme is designed to help the least efficient homes first.

There is also a route called eco4 Flex, which allows local authorities to refer households that would not otherwise qualify under the standard criteria, provided they can show the household is in fuel poverty or vulnerable to living in a cold home. This widens who can access funding beyond strict benefit eligibility, so it is worth checking with your local council even if you are unsure whether you qualify under the main scheme.

Wall Insulation Under Eco4

Cavity wall insulation is one of the most commonly delivered measures under eco4, largely because it is quick to install and delivers a strong energy performance improvement for a relatively modest cost. For solid wall properties, where cavity fill is not an option, external or internal wall insulation can also be funded under the same scheme, alongside other structural insulation and heating measures.

Because eco4 favours a whole house approach, wall insulation is often bundled with other measures during the same assessment. If your walls and your heating system are both underperforming, a single eco4 application can address both, which is generally more cost effective than tackling them separately over time.

Why the December 2026 Deadline Matters

The eco4 obligation period was originally set to run from July 2022 to 31 March 2026. It has since been extended, and energy suppliers must now deliver all remaining qualifying measures in full no later than 31 December 2026. Ofgem’s own delivery guidance confirms this extended deadline, rather than the earlier date still mentioned in some older articles.

In practice, this means the closer you get to the end of the year, the harder it becomes to complete an application, get a survey booked, and have the work carried out in time. Suppliers have finite obligations to fulfil, and demand tends to spike as deadlines approach, so acting earlier rather than later gives you a meaningfully better chance of securing funding before the scheme closes.

What Happens After Eco4 Ends

There is no confirmed like for like successor to eco4 announced at this stage. Some support continues through the wider Warm Homes Plan, including grants and low or zero interest loans for households above the strict benefit thresholds, but the specific structure of eco4 itself is not guaranteed to continue in its current form.

This is exactly why the closing window matters. If wall insulation funding through eco4 is available to you now, waiting until the scheme’s future is clearer could mean missing the opportunity entirely. Households who might otherwise qualify should treat 2026 as the year to check eligibility, not a future one.

How to Check Your Eligibility

Because eco4 is delivered through obligated energy suppliers rather than a single central application, the fastest route is usually to check with your current energy supplier directly, or to search for eco4 Flex through your local council if you are unsure whether you meet the standard benefit criteria. A reputable installer can also carry out an initial eligibility check as part of a free survey.

If your home has solid walls rather than a cavity, it is worth understanding the cost difference before applying, since external wall insulation involves different installation requirements and a different funding pathway under eco4 than standard cavity fill.

Getting Started Before the Deadline

The safest approach is to start the eligibility check now rather than closer to the end of the year, since installer capacity tightens as suppliers rush to meet their obligations before 31 December 2026. For a full breakdown of how wall insulation works, what it costs without funding, and which method suits your property, our complete guide to wall insulation is a useful starting point.

If you think you might qualify, get in touch with our team today for an eligibility check before this year’s eco4 funding window closes for good.

Internal Wall Insulation for Older UK Homes: What You Need to Know in 2026

Internal wall insulation is one of two approaches available to homeowners with solid walls who want to improve their property’s thermal performance. It is the right solution in some situations and the wrong one in others. This guide covers how it works, what it costs, when it makes sense, and when a different approach would serve you better.

Why Older Homes Need Wall Insulation

Properties built before the 1920s in the UK have solid walls rather than cavities. A solid wall loses far more heat than a properly insulated cavity wall. In practical terms, an uninsulated solid wall can account for up to 45% of a home’s total heat loss. This shows up directly on your energy bills every winter and on your EPC rating.

For homeowners in Victorian terraces, Edwardian semis, or any other solid wall property, wall insulation is one of the highest-impact improvements available. The question is whether internal or external insulation is the right approach for your specific situation.

What Is Internal Wall Insulation?

Internal wall insulation involves adding an insulating layer to the inside face of your external walls. The insulation sits behind a new plasterboard finish, which creates a new internal wall surface. From inside the room, the result looks like any other plastered wall.

There are two main methods. The first is rigid insulation boards bonded directly to the existing wall surface using adhesive. This is the thinner of the two options and suits walls that are in good condition and relatively flat. The second is a timber or metal stud frame built against the wall and packed with mineral wool or rigid insulation. This allows for thicker insulation but takes up more floor space.

Both methods require the room to be cleared, the new wall to be installed and finished, and the room to be fully redecorated afterwards. Radiators, sockets, switches, window sills, and skirting boards all need to be removed and refitted as part of the process.

What Are the Advantages of Internal Wall Insulation?

It Does Not Change the External Appearance

Internal wall insulation has no visible impact on the outside of the building. This makes it the only practical option for listed buildings, properties in conservation areas, and homes on terraces where the street-facing elevation must remain unchanged.

If your property is subject to planning restrictions that prevent external changes, internal insulation is the route to take. Always confirm this with your local planning authority before proceeding.

It Can Be Done Room by Room

Unlike external wall insulation, which treats the whole building at once, internal insulation can be installed one room at a time. This allows you to spread the cost and disruption over a longer period. If you are renovating a room anyway, adding internal wall insulation to the external walls as part of that project is a cost-effective way to improve the thermal performance of the space.

It Can Achieve a Good Thermal Result

A well-specified internal insulation system can deliver a U-value of 0.3 W/m2K or below, which matches the performance of a good external system. The key is using sufficient thickness of the right insulation material and detailing the junctions carefully to minimise thermal bridging.

What Are the Disadvantages of Internal Wall Insulation?

It Reduces Your Floor Space

Every wall treated with internal insulation moves inward. Depending on the insulation thickness and method, you may lose between 80mm and 150mm on each external wall face. In a large room this is barely noticeable. In a small bedroom or narrow hallway, it can make a real difference to how the space feels and functions.

It Is More Disruptive Than External Insulation

External wall insulation takes place entirely outside the building. You live in the house as normal while it happens. Internal insulation requires each treated room to be cleared, stripped, and rebuilt. If you are insulating all external walls across the whole house, the disruption is substantial.

It Leaves Cold Bridges at Junctions

One of the technical limitations of internal wall insulation is that it is difficult to carry through floor and ceiling junctions without significant additional work. Cold bridges at these junctions reduce the overall thermal performance of the system and can lead to condensation at the junction points. A competent installer will address this as far as possible, but the issue is more pronounced with internal insulation than with external.

It Does Not Address External Wall Condition

External wall insulation wraps the building and protects the existing wall surface from weathering. Internal insulation does nothing to address the external condition of the wall. If the wall has cracked pointing, damaged render, or any other defect that allows moisture to penetrate, these issues need to be resolved separately.

How Much Does Internal Wall Insulation Cost in 2026?

Internal wall insulation typically costs between £4,000 and £14,000 for a standard semi-detached property in 2026, before accounting for redecoration, moving radiators and sockets, and other associated works. When these additional costs are included, the gap between internal and external insulation narrows significantly.

Grant funding is less widely available for internal wall insulation than for external. However, some ECO4 and Great British Insulation Scheme funding does apply. Check your eligibility at gov.uk (https://www.gov.uk). The Energy Saving Trust also provides guidance at energysavingtrust.org.uk (https://www.energysavingtrust.org.uk).

For properties where external wall insulation is appropriate, that option typically delivers stronger thermal performance and a better EPC rating improvement with less internal disruption. For a full comparison, visit ecoinsulation.co.uk.

When Is Internal Wall Insulation the Right Choice?

Internal wall insulation is the right choice when external insulation is not permitted due to planning restrictions, when you are renovating a specific room and want to combine the work, or when the property is a flat where only certain walls need treatment and coordinating an external project with the wider building is not practical.

For most whole-house projects on standard solid wall properties outside conservation areas, external wall insulation delivers a better overall result with less disruption to daily life.

For EPC certificate guidance and how an improved wall insulation rating affects your property, visit epccertificates.co.uk. For floor insulation, which is often a complementary measure in older properties, visit floorinsulation.co.uk.

Contact Us

If you are considering internal wall insulation for an older UK property in 2026, contact us today. We will survey your home, confirm whether internal or external insulation is the more appropriate solution, check your eligibility for any available grant funding, and give you a clear, no-obligation recommendation.