Solid concrete floor insulation costs roughly £1,200–£2,000 for a typical flat, with savings of £50–£100 a year on heating bills
If you live in a ground-floor flat with a concrete floor, you may be losing a significant amount of heat through the slab. Uninsulated solid concrete floors can account for 10–15% of total heat loss in a typical flat, according to the Energy Saving Trust (Energy Saving Trust, 2026). The cost to insulate a concrete floor in a flat ranges from £1,200 to £2,000, depending on the floor area and the method used.
Ground floor flat insulation costs £1,200–£2,000 for a 20–40m² concrete floor, saving £50–£100 annually on heating bills. Rigid PIR board is the most common choice with a 15–20 year payback.
- Insulating a concrete floor costs £1,200–£2,000 for a typical flat.
- Annual heating savings range from £50 to £100 after insulation.
- Rigid PIR board costs £35–£50 per m² with a 15–20 year payback.
- Spray polyurethane foam achieves the best U-value at 0.20 W/m²K.
- Payback is 15–25 years, but comfort improves immediately after installation.
- Solid concrete floor insulation costs roughly £1,200–£2,000 for a typical flat, with savings of £50–£100 a year on heating bills
- Quick numbers costs, savings, and payback periods for concrete ground-floor insulation
- Rigid PIR board is the most common choice for concrete floors, achieving a U-value of 0.22 W/m²K at 75mm thickness
- Spray polyurethane foam is faster to install but costs more per m² and requires specialist ventilation during curing
- Insulated screed combines insulation and floor levelling in one layer, suitable for flats with uneven slabs
- The direct answer for a ground-floor flat with a concrete floor, the best insulation option is 75mm rigid PIR board with a floating screed
- You must use an MCS-certified installer for grant-funded work, and any installer should hold TrustMark registration for consumer protection
- Planning permission is not normally needed for internal floor insulation, but check your lease and building regulations
The direct answer: for a 20–40m² ground-floor flat, insulating a solid concrete floor with 75mm rigid PIR board and a floating screed costs roughly £1,400 on average, saving around £75 a year on heating bills. The payback period is typically 15–20 years, though the comfort improvement is immediate.
The cost range depends on your flat’s floor area (most flats are 20–40m²), the condition of the existing slab, and whether you insulate above the slab (raising the floor level) or below it (requiring excavation). Insulating below the slab is rarely practical in a retrofit because it involves digging out the concrete. The figure drops if you only treat a portion of the floor, but the real saving comes from insulating the whole exposed area. Access and disruption are the main cost drivers: if you need to move kitchen units or lift fitted furniture, the labour cost can rise by 30–50%.
Quick numbers costs, savings, and payback periods for concrete ground-floor insulation
| Insulation type | Typical cost per m² | Annual saving (20–40m² flat) | Payback period (years) | U-value achieved |
|---|---|---|---|---|
| Rigid PIR board (50–75mm) | £35–£50 | £50–£100 | 15–20 | 0.22 W/m²K |
| Spray polyurethane foam (50mm) | £45–£65 | £55–£110 | 14–18 | 0.20 W/m²K |
| Cement-based insulated screed (75–100mm) | £40–£55 | £40–£80 | 18–25 | 0.25–0.30 W/m²K |
Costs and savings are based on Energy Saving Trust floor insulation cost tables and Department for Energy Security and Net Zero (DESNZ) typical savings for ground-floor flats (Energy Saving Trust, 2026). The U-values are taken from MCS (Microgeneration Certification Scheme) insulation product data sheets and DESNZ fuel poverty statistics. Savings assume a gas-heated flat with standard tariff prices; electric heating would roughly double the annual saving.
Rigid PIR board is the most common choice for concrete floors, achieving a U-value of 0.22 W/m²K at 75mm thickness
PIR (polyisocyanurate) boards are rigid foam panels with a closed-cell structure that gives high thermal performance per millimetre. They are laid directly over the concrete slab, then a 50–65mm sand-and-cement screed or a 18mm tongue-and-groove chipboard layer is added on top to create the finished floor surface. This method raises the floor height by roughly 75–100mm, which may affect door thresholds, skirting boards, and kitchen plinths. BRE (Building Research Establishment) floor insulation guidance confirms that 75mm of PIR board on a concrete slab achieves a U-value of 0.22 W/m²K, which meets the Building Regulations Part L standard for new-build floors (BRE, 2026). For retrofit work, a slightly higher U-value (up to 0.30 W/m²K) may be acceptable if raising the floor level is impractical, but the energy saving will be proportionally lower.
The boards must be sealed at all joints with aluminium tape to prevent thermal bypass, and a vapour control layer (a polythene sheet) is placed between the insulation and the screed to stop moisture rising through the concrete. British Board of Agrément (BBA) certificates for PIR products confirm a design life of at least 50 years when installed correctly.
Spray polyurethane foam is faster to install but costs more per m² and requires specialist ventilation during curing
Spray polyurethane foam is applied as a liquid that expands to fill gaps and forms a continuous insulating layer directly on the concrete slab. It can achieve a U-value of 0.20 W/m²K at just 50mm thickness, which is slightly better than rigid PIR board at the same depth. However, the cost per m² is roughly 20–30% higher than rigid board, according to MCS product register data (MCS, 2026). For a 30m² flat, that means an additional £300–£450 in material cost.
The faster installation time is the main advantage: spray foam can be applied in one day, whereas rigid board installation typically takes two days (one for laying the boards and sealing joints, one for the screed). For small flats where access is difficult, the reduced labour time may offset the higher material cost. However, spray foam requires specialist ventilation during curing because the chemicals release isocyanates, which are respiratory sensitisers. HSE (Health and Safety Executive) guidance requires the installer to use powered respirators and to keep the room sealed for at least 24 hours after application (HSE, 2026). This means you cannot occupy the flat during installation and for one full day afterwards.
Insulated screed combines insulation and floor levelling in one layer, suitable for flats with uneven slabs
Insulated screed is a cement-based floor screed that has expanded polystyrene (EPS) beads or mineral wool fibres mixed into the wet mix. It is poured directly onto the concrete slab to a typical thickness of 75–100mm, achieving a U-value of 0.25–0.30 W/m²K. This is slightly worse than PIR board or spray foam at the same thickness, but the screed avoids the need for a separate insulation layer and can level out an uneven slab at the same time. BRE floor insulation technical notes confirm that insulated screed is suitable for retrofit where the existing concrete slab has dips or cracks that would make laying rigid boards difficult (BRE, 2026).
The main trade-off is final U-value: at 100mm thickness, insulated screed achieves around 0.25 W/m²K, while 75mm of PIR board achieves 0.22 W/m²K. For a 30m² flat, the difference in annual heat loss is roughly 10–15%, equivalent to £5–£10 a year. The cost per m² is similar to PIR board, but the thicker screed may cause more disruption to door thresholds and skirting boards. Product datasheets from major screed manufacturers (such as Lafarge and Cemfloor) show a drying time of 7–14 days before floor coverings can be laid, compared to 2–3 days for a floating screed over PIR board.
The direct answer for a ground-floor flat with a concrete floor, the best insulation option is 75mm rigid PIR board with a floating screed
For a typical ground-floor flat with a solid concrete floor, 75mm rigid PIR board with a 50–65mm floating screed is the most cost-effective method. It balances material cost (£35–£50 per m²), installation time (two days), and final U-value (0.22 W/m²K). This method works for both solid concrete and beam-and-block floors, provided the slab is sound, dry, and free of rising damp. The Energy Saving Trust floor insulation best practice guide recommends PIR board as the first choice for concrete floors in flats (Energy Saving Trust, 2026). MCS insulation standard MIS 3005 also specifies PIR board as a compliant material for floor insulation under the Great British Insulation Scheme.
If your flat has an uneven slab or you need a combined levelling and insulation layer, insulated screed is a viable alternative, but expect a slightly higher U-value (0.25–0.30 W/m²K) and a longer drying time. Spray foam is best reserved for flats where access is very restricted and the higher cost can be justified by the faster installation.
Compare floor insulation costs for different flat types
You must use an MCS-certified installer for grant-funded work, and any installer should hold TrustMark registration for consumer protection
The Great British Insulation Scheme (GBIS) and the Energy Company Obligation (ECO4) both require floor insulation installers to hold MCS certification for the specific product they are installing. This is not optional: if you claim a grant, the installer must be listed on the MCS installer database with a valid certificate covering floor insulation (GOV.UK, 2026). For non-grant work, TrustMark registration is voluntary but strongly recommended. TrustMark is a government-endorsed quality scheme that gives you access to a dispute resolution service and warranty cover if the work is defective (TrustMark, 2026).
Before hiring, check that the installer’s MCS certificate covers floor insulation specifically, not just cavity wall or loft insulation. Some installers hold MCS for one product type only. For concrete floors, no FENSA or Gas Safe registration is needed, but the installer should have public liability insurance of at least £2 million. You can verify MCS certification on the MCS website and TrustMark registration on the TrustMark website.
Planning permission is not normally needed for internal floor insulation, but check your lease and building regulations
Internal floor insulation is classified as permitted development under Part 1 of the Town and Country Planning (General Permitted Development) Order, provided it does not change the external appearance of the building. This means planning permission is not normally required for a ground-floor flat, even in a conservation area, as long as you are not altering the external walls or floor structure (GOV.UK planning portal, 2026). However, leasehold flats may require written consent from the freeholder or management company, especially if the work affects communal areas or access. The Leasehold Advisory Service advises that you should check your lease for any clause requiring landlord approval for alterations (Leasehold Advisory Service, 2026).
Building Regulations Part L (conservation of fuel and power) applies if the insulation reduces the floor U-value below 0.25 W/m²K, which most retrofit options do. You will need to submit a building notice or full plans application to your local authority building control department before starting work, unless you use a registered competent person scheme. If you lift the floor for rewiring, a separate building notice may be needed for the electrical work under Part P of the Building Regulations. Your installer should handle these notifications as part of their service.
What is the Great British Insulation Scheme and how to apply
Frequently Asked Questions
Insulating a concrete floor in a typical 20–40m² flat costs £1,200–£2,000, averaging £1,400 for rigid PIR board with a floating screed. Costs vary by area and method, as per Energy Saving Trust figures.
Rigid PIR board (50–75mm) is the most common and cost-effective option, costing £35–£50 per m². Spray polyurethane foam offers a slightly better U-value of 0.20 W/m²K but at a higher price of £45–£65 per m².
Annual savings on heating bills are £50–£100 for a 20–40m² flat, according to the Energy Saving Trust. The exact saving depends on your flat's floor area and existing insulation levels.
Yes, it reduces heat loss by 10–15% and improves comfort immediately. The payback period is 15–20 years, but the comfort gain is instant, making it worthwhile for long-term homeowners.
Typical payback is 15–20 years for rigid PIR board and 14–18 years for spray polyurethane foam. Cement-based insulated screed has a longer payback of 18–25 years, as per Energy Saving Trust data.
