Home Insulation Cost UK 2026: What Installers Charge and How to Get It Free via ECO4

Quick Answer

Home insulation in the UK costs £300–£600 for loft insulation (blown or batt), £400–£600 for cavity wall insulation, and £5,000–£15,000 for solid wall insulation (external or internal). Thousands of properties qualify for free insulation under the government's ECO4 scheme — primarily households on means-tested benefits or with a low EPC rating. Even without a grant, loft and cavity wall insulation pay back through energy savings within 2–5 years. Solid wall insulation takes 15–30 years to pay back at current energy prices.

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Types of Home Insulation and Their Costs

Loft Insulation

The most cost-effective single insulation measure available. Heat rises, and in an uninsulated home up to 25% of heat loss occurs through the roof.

Blown (loose-fill) mineral wool or cellulose:

• Blown into the loft space between joists
• Fast to install (2–4 hours)
• Cost: £300–£600 for a typical semi-detached house
• Recommended depth: 270mm (current Building Regulations standard)

Loft boards / accessible loft:

• If you use your loft for storage, insulation must go below the boards (between joists) AND above (using rigid insulation between counter-battens)
• More complex — allow £600–£1,200

Flat roof insulation:

• Internally fitted rigid board insulation or externally as part of a re-roofing project
• £1,500–£5,000 depending on area

Annual saving: A well-insulated loft saves £150–£300/year in heating bills (depending on property size and existing insulation depth). Payback period: 1–3 years.

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Cavity Wall Insulation

Most UK homes built between 1920 and 1990 have a cavity wall — two layers of brick with a hollow space between. Filling this cavity with mineral wool, polystyrene beads, or injected foam significantly reduces heat loss.

Process: Installers drill small holes in the external mortar joints every 1–1.5 metres, inject insulation, and repoint the holes. Takes half a day. No internal disruption.

Cost: £400–£600 for a typical 3-bedroom semi-detached house

What affects price:

• House size
• Wall condition (damaged or damp walls may not be suitable)
• Cavity width (narrow cavities are harder to fill fully)

Caution: Cavity wall insulation should only be installed in walls with no signs of damp and in areas with average or low exposure to driving rain. Incorrectly installed cavity wall insulation can cause damp penetration — use a BBA-certified installer and confirm a pre-installation survey is conducted.

Annual saving: £150–£250/year in energy bills. Payback: 2–4 years.

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Solid Wall Insulation

Pre-1920 homes typically have solid walls (225mm brick or stone with no cavity). These are much harder and more expensive to insulate.

External Wall Insulation (EWI): Rigid insulation boards are fixed to the outside of the property, covered with a render or cladding finish.

Requires scaffolding, which adds £1,000–£3,000.

Internal Wall Insulation (IWI): Rigid insulation boards or stud walls with mineral wool insulation fixed to internal faces of external walls.

IWI reduces internal room dimensions by 75–100mm per wall and requires skirting boards, architraves, and sockets to be re-fixed. More disruptive than EWI but cheaper.

Annual saving: £200–£400/year. Payback: 20–40 years at current prices without grants.

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Floor Insulation

Often overlooked. Suspended timber floors (common in Victorian and Edwardian houses) can be insulated from below using mineral wool or rigid board installed between joists.

Cost: £500–£2,000 depending on property size and access

Solid concrete floors: Rigid insulation board laid beneath a new screed — more expensive and disruptive (£3,000–£8,000) but worthwhile during a major renovation.

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Underfloor Heating and Insulation

Underfloor heating should always be installed on top of insulation. Without floor insulation, heat is lost downward rather than rising into the room.

If installing UFH in a renovation: add rigid PIR insulation board (50mm minimum) beneath the screed. Cost per m²: £15–£30/m².

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ECO4: Free Insulation for Qualifying Homes

The Energy Company Obligation (ECO4) scheme requires large energy suppliers to fund energy efficiency improvements for low-income or fuel-poor households. The current phase (ECO4) runs until March 2026, with an extension expected.

Who qualifies:

• Households receiving means-tested benefits (Universal Credit, Pension Credit, Child Tax Credit, Housing Benefit, etc.)
• Properties with an EPC rating of D, E, F, or G (i.e., below average efficiency)
• Some local authority referral schemes cover households not on benefits if the property has very low EPC rating

What's covered:

• Loft insulation
• Cavity wall insulation
• Solid wall insulation (external or internal)
• Heat pumps
• Solar panels (in some cases)

How to apply: Contact energy suppliers (British Gas, E.ON, EDF, Octopus, OVO, etc.) directly and ask for an ECO4 assessment. Alternatively, use the government's Simple Energy Advice service or a TrustMark-registered ECO4 installer.

Important: Only use TrustMark-registered installers for ECO4 work. Unregistered "free insulation" companies that cold-call or door-knock have been involved in fraudulent schemes — verify registration before allowing any work to proceed.

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The Great British Insulation Scheme (GBIS)

Running alongside ECO4, the Great British Insulation Scheme (GBIS) offers single-measure insulation grants to a broader group — including households not on benefits, if the property has a low EPC rating (D or below) and is in council tax band A–D.

Typical contribution from GBIS: covers 50–100% of single-measure insulation (loft or cavity wall) in eligible properties.

Check eligibility at gov.uk/great-british-insulation-scheme.

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Installer Rates: What Insulation Installers Charge

Most insulation work is quoted as a fixed price for the complete job. Cavity wall and loft insulation companies typically price per job rather than per day.

For ECO4 work, installers are paid by the energy company — you pay nothing if eligible.

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Choosing the Right Insulation Measure for Your Property

If you're unsure, commission an EPC assessment (£60–£120) or request a free energy assessment through Simple Energy Advice. This identifies which measures will have the highest impact in your specific property.

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Frequently Asked Questions

Does cavity wall insulation cause damp? Poorly installed cavity wall insulation in properties with existing damp or in high-exposure areas (driving rain) can introduce damp problems. Use a BBA-certified installer, ensure a proper pre-installation survey is done, and check whether your wall is suitable. The Cavity Insulation Guarantee Agency (CIGA) provides 25-year guarantees on approved installations.

Can I install loft insulation myself? Yes — top-up loft insulation using mineral wool rolls is one of the few genuinely practical DIY insulation tasks. Wear a dust mask, eye protection, and gloves. Ensure the existing insulation isn't asbestos (common in homes built before 1985 using loose vermiculite). Do not block eaves or ventilation points.

How do I know if my home has cavity walls or solid walls? Measure the wall thickness. If the external wall is 220–270mm thick, it's likely a solid brick wall. If it's 280mm+, it's probably a cavity wall. Alternatively, check a nearby door or window reveal — cavity walls have a distinctive inner and outer leaf visible in the jamb.

Will insulation make my house feel smaller? External wall insulation adds 80–120mm to the outside of the property — no internal impact. Internal wall insulation removes 75–100mm of internal space per insulated wall — noticeable in smaller rooms. Consider this before choosing IWI over EWI.

Is there VAT on insulation installation? From April 2022, VAT on residential energy-saving materials (including insulation) was reduced to 0% in the UK. This means insulation installations are VAT-free, reducing costs by 20% compared to pre-2022 pricing.