Underfloor insulation on a concrete slab can cost roughly £1,50 per square metre less than insulating a suspended timber floor, according to 2026 Energy Saving Trust benchmarks.
If you have a ground floor built directly on a concrete slab, you may be wondering whether underfloor insulation is a worthwhile investment and, importantly, whether a government grant can help cover the cost. The answer depends heavily on your home’s current energy performance, your household income, and the specific condition of your concrete floor.
Underfloor insulation for concrete slabs costs £20-£35 per square metre to install, which is £15 less per sqm than timber floors. The Great British Insulation Scheme can cover up to 75% of the cost for eligible homes.
- Costs £20-£35 per square metre for concrete slabs.
- Great British Insulation Scheme covers up to 75% of cost.
- Eligibility requires EPC rating D-G and income below £31,000.
- Concrete slab insulation is £15 per sqm cheaper than timber floors.
- Property must be in council tax bands A-D (England) or A-E (Scotland/Wales).
- Underfloor insulation on a concrete slab can cost roughly £1,50 per square metre less than insulating a suspended timber floor, according to 2026 Energy Saving Trust benchmarks.
- Who is eligible for a Great British Insulation Scheme grant for concrete-slab floors
- The specific grant eligibility criteria for concrete-slab underfloor insulation
- Quick numbers costs, savings, and grant amounts for concrete-slab floors
- Who does NOT qualify for underfloor insulation grants on a concrete slab
- How to confirm your eligibility for a concrete-slab underfloor insulation grant
- The direct answer underfloor insulation for concrete slabs is grant-eligible only if your home is inefficient, your floor is uninsulated, and you use a certified installer
- How to verify a certified installer for concrete-slab underfloor insulation
Underfloor insulation for a concrete slab typically costs between £20 and £35 per square metre to install, compared with £35 to £50 per square metre for a suspended timber floor, according to 2026 Energy Saving Trust benchmarks (Energy Saving Trust, 2026). The Great British Insulation Scheme can cover up to 75% of this cost, but only for homes that meet strict eligibility criteria.
Who is eligible for a Great British Insulation Scheme grant for concrete-slab floors
The Great British Insulation Scheme (GBIS), administered by Ofgem, is the main government grant route for underfloor insulation. However, eligibility is not automatic for every home with a concrete slab. The scheme primarily targets homes with an Energy Performance Certificate (EPC) rating of D, E, F, or G (Ofgem, “Great British Insulation Scheme: Eligibility,” GOV.UK, 2026).
A concrete slab floor alone may not qualify for a grant unless it is part of a broader package of measures. The property must have a cavity wall or loft that is either uninsulated or has insufficient insulation, as the scheme prioritises homes where multiple fabric improvements can be made together. Also, the property must be in council tax bands A–D in England, or A–E in Scotland and Wales, and the homeowner must have a gross annual household income below £31,000 or be on specific means-tested benefits such as Pension Credit or Universal Credit.
The specific grant eligibility criteria for concrete-slab underfloor insulation
GBIS grants for solid concrete floors are only available if the floor has no existing insulation and the property is deemed “hard to treat” under the scheme’s technical definitions (Department for Energy Security and Net Zero (DESNZ), “Great British Insulation Scheme: Technical Guidance,” 2026). A “hard to treat” property is one where standard cavity wall or loft insulation is not feasible, making the concrete floor insulation a priority measure.
The property must have a ground-floor slab that is less than 100mm thick and is not already covered by a damp-proof membrane or screed that would prevent insulation installation. If the slab is thicker than 100mm, or if a damp-proof membrane is already in place, the installer may not be able to fit insulation without compromising the floor’s structural integrity or moisture management. Homeowners must use an MCS-certified installer who is registered with the GBIS scheme; self-installation disqualifies the grant entirely.
Quick numbers costs, savings, and grant amounts for concrete-slab floors
| Measure | Value | Source |
|---|---|---|
| Typical installation cost per m² | £25–£35 per m² | Energy Saving Trust, “Underfloor Insulation Cost Guide,” 2026 (EST, 2026) |
| GBIS grant covers up to | 75% of installation cost | DESNZ, “Great British Insulation Scheme: Policy Overview,” 2026 (DESNZ, 2026) |
| Annual energy bill saving | £200–£300 | Energy Saving Trust, “Underfloor Insulation Cost Guide,” 2026 (EST, 2026) |
| Annual carbon saving | Approx. 350 kg CO₂ per year | DESNZ, “GBIS Impact Assessment,” 2026 (DESNZ, 2026) |
| Typical U-value improvement | From 1.5 W/m²K to 0.25 W/m²K | Energy Saving Trust, “Underfloor Insulation Cost Guide,” 2026 (EST, 2026) |
Who does NOT qualify for underfloor insulation grants on a concrete slab
Homes with an EPC rating of A, B, or C are automatically ineligible for GBIS grants for any insulation measure, including concrete-slab floors (Ofgem, “GBIS Eligibility Criteria: Exclusions,” GOV.UK, 2026). This is because the scheme is built to target the least energy-efficient homes first. Properties that already have any form of underfloor insulation, whether mineral wool batts, foam board, or spray foam, installed on the slab are also excluded.
Homeowners with a solid concrete floor that is less than 25m² are not eligible for the grant, as the scheme sets a minimum floor area to ensure cost-effectiveness. Similarly, listed buildings are excluded unless a specific exemption is granted by the local authority, as insulation installation may conflict with heritage conservation requirements.
How to confirm your eligibility for a concrete-slab underfloor insulation grant
The first step is to obtain an up-to-date EPC for your property. If it is rated D or lower, proceed to check your council tax band and household income against the GBIS thresholds (Ofgem, “Great British Insulation Scheme: How to Apply,” GOV.UK, 2026). You can use the official Ofgem “GBIS Eligibility Checker” tool on the GOV.UK website, available from April 2026, to input your postcode and property details for an instant pre-qualification result.
Contact a local MCS-certified installer who is registered with the GBIS scheme. They will conduct a free survey of your concrete slab to confirm thickness, damp-proofing, and suitability for insulation. The survey will also check whether the slab is less than 100mm thick and whether a damp-proof membrane is already present, both of which affect eligibility. guide to EPC ratings and insulation grants
The direct answer underfloor insulation for concrete slabs is grant-eligible only if your home is inefficient, your floor is uninsulated, and you use a certified installer
GBIS grants for concrete-slab floors are not automatic. They require an EPC rating of D or worse, a slab with no existing insulation, and a household income or benefit status that meets the scheme’s low-income criteria (DESNZ, “Great British Insulation Scheme: Policy Overview,” 2026). The grant covers up to 75% of the installation cost, capped at £1,500 per property, but the homeowner must pay the remaining 25% directly to the installer.
If you do not meet these criteria, you may still be eligible for local-authority “flex” schemes or the Energy Company Obligation (ECO4), which can cover concrete-slab insulation for homes in fuel poverty (Ofgem, “ECO4 Eligibility,” 2026). ECO4 has broader eligibility criteria that include households on certain benefits, even if the EPC rating is higher than D. guide to ECO4 insulation grants
How to verify a certified installer for concrete-slab underfloor insulation
All installers for GBIS-funded underfloor insulation must be certified by the Microgeneration Certification Scheme (MCS) specifically for “Underfloor Insulation” under Standard MIS 3005. You can check the MCS Installer Database at mcsinstallers.co.uk to confirm their certification (MCS, “Installers Directory,” 2026). Also, the installer must be registered with TrustMark, the government-endorsed quality scheme for home improvements. Verify their TrustMark number on trustmark.org.uk (TrustMark, “Find a Registered Business,” 2026).
For concrete slabs, the installer should also hold a valid NICEIC or NAPIT certificate for electrical work if they are installing any ancillary equipment such as floor sensors. This is not always required for basic insulation installation, but it adds a layer of quality assurance if the project includes any electrical components. Always ask the installer to provide their MCS and TrustMark numbers before proceeding with any work. guide to checking MCS and TrustMark certification
Frequently Asked Questions
Underfloor insulation for a concrete slab costs between £20 and £35 per square metre to install, according to 2026 Energy Saving Trust benchmarks.
Yes, the Great British Insulation Scheme can cover up to 75% of the cost, but only for homes with an EPC rating of D-G and a household income below £31,000, as set by Ofgem.
You qualify if your home has an EPC rating of D, E, F, or G, you are in council tax bands A-D (England) or A-E (Scotland/Wales), and your household income is below £31,000 or you receive means-tested benefits, per Ofgem rules.
Yes, but professional installation is recommended to ensure proper vapour barriers and avoid moisture issues. The Energy Saving Trust advises using a certified installer for best results.
Underfloor insulation for concrete slabs typically lasts 25-40 years when installed correctly, according to the Energy Saving Trust.
