Floor insulation for a concrete slab costs roughly £25 to £50 per square metre installed
The total cost for a typical three-bedroom semi-detached home, which has a ground floor area of roughly 55 m², is between £1,375 and £2,750. This range comes from Energy Saving Trust typical cost data (Energy Saving Trust, 2026). The price varies by insulation material, the thickness required, and whether the slab is solid or suspended.
PIR (polyisocyanurate) board is the most common material. EPS (expanded polystyrene) is a cheaper alternative. Mineral wool is used less often for solid slabs. Labour for cutting and fitting insulation boards adds roughly £10 to £15 per m² (Checkatrade average rates, 2026). If you combine floor insulation with underfloor heating installation, that adds a further £25 to £40 per m².
The typical annual saving from insulating a concrete slab floor is £100 to £200 on heating bills
Savings depend on the existing floor U-value compared with the target. An uninsulated solid concrete slab typically has a U-value of 0.7 to 0.9 W/m²K. Building Regulations Part L (2021, updated 2025) requires a target of 0.22 W/m²K (GOV.UK, Approved Document L, 2025).
A 55 m² floor upgrade saves approximately 800 to 1,200 kWh per year (Energy Saving Trust, “Domestic Floor Insulation” report, 2026). At the 2026 average gas price of 6.24 p/kWh under the Ofgem price cap for October to December 2026 (Ofgem, 2026), this equates to £50 to £75 saved annually for gas-heated homes. Electric heating doubles the saving to £100 to £200 per year. The payback period is 10 to 25 years for gas heating, but 5 to 12 years for electric heating.
Quick numbers, floor insulation cost, saving, and U-value table
| Metric | Value | Source |
|---|---|---|
| Cost per m² (materials + labour) | £25–£50 | EST cost database, 2026 |
| Typical annual saving (gas) | £50–£75 | EST + Ofgem price cap Oct–Dec 2026 |
| Typical annual saving (electric) | £100–£200 | EST + Ofgem price cap Oct–Dec 2026 |
| Target U-value (Building Regs) | 0.22 W/m²K | Approved Document L, 2021 (2025 update) |
| Uninsulated slab U-value | 0.7–0.9 W/m²K | BRE/EST standard values |
| Recommended insulation thickness (PIR) | 60–100 mm | Manufacturers’ data (Kingspan, Celotex) |
| Payback period (gas heating) | 10–25 years | EST calculation |
| Payback period (electric heating) | 5–12 years | EST calculation |
Floor insulation for a concrete slab works by adding a layer of rigid insulation board on top of the slab, then a new screed or flooring deck
The standard method is to lay 60 to 100 mm of PIR or EPS board directly onto the cleaned, damp-proofed concrete slab. A vapour control layer (VCL) is placed between the slab and insulation to prevent moisture rising (NHBC standards, 2026). A 50 to 75 mm sand/cement screed or a floating timber deck is then installed over the insulation to create the finished floor surface.
Thermal bridging at the edges must be addressed by insulating the perimeter up the wall (BRE “Thermal Bridging Guide”, 2026). For suspended concrete slabs, such as beam-and-block, insulation is often placed between the beams or below the slab. The on-top method described above is most common for solid slabs.
Lay rigid insulation boards on the slab, seal all joints, then screed over
The process is: clean slab, apply damp-proof membrane if none exists, lay insulation boards tightly with staggered joints, tape all joints, install edge insulation strips, then pour or float screed or lay a timber deck. The insulation must be continuous, with no gaps or compression (MCS standard for floor insulation, 2026).
The final U-value must be calculated using the BRE “U-value Calculator”, available free on GOV.UK. how to calculate U-values for floor insulation This ensures compliance with Building Regulations.
The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing.
The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing. In England, this means bands A to D (GOV.UK, “ECO4: guidance”, 2026). The grant typically covers 100% of the cost for qualifying households. Otherwise, you must self-fund.
For self-funders, the installation must be carried out by an MCS-certified installer to qualify for any future grant or certification (MCS website, 2026). Check eligibility at gov.uk/great-british-insulation-scheme or via your energy supplier. full guide to GBIS eligibility criteria
You must use an MCS-certified installer for floor insulation to meet Building Regulations and grant requirements
All floor insulation work must comply with Part L of the Building Regulations, which covers conservation of fuel and power. A registered installer who is MCS, TrustMark, or FENSA certified for associated glazing can self-certify (GOV.UK, “Building Regulations: Approved Document L”, 2026). MCS certification is mandatory for any installation claimed under ECO4 or GBIS (MCS “Installation Standards for Floor Insulation”, 2026).
For gas-safe work, such as moving a boiler to access the floor, a Gas Safe Register engineer is required (Gas Safe Register, 2026). Electrical work, such as underfloor heating connections, must be done by a NICEIC or NAPIT registered electrician under Part P of the Building Regulations (GOV.UK, Part P, 2026).
Frequently Asked Questions
Floor insulation for a concrete slab costs £25 to £50 per square metre installed, according to Energy Saving Trust cost data for 2026. Labour adds roughly £10 to £15 per m² based on Checkatrade average rates.
Yes, floor insulation on a concrete slab is worth it, especially for electric-heated homes. Annual savings reach £100 to £200 per year according to the Energy Saving Trust, with a payback of 5 to 12 years.
Building Regulations Part L requires a target U-value of 0.22 W/m²K for floor insulation, as confirmed in Approved Document L (2025) from GOV.UK. An uninsulated solid concrete slab typically has a U-value of 0.7 to 0.9 W/m²K.
PIR (polyisocyanurate) board is the most common material for concrete slab floors. EPS (expanded polystyrene) is a cheaper alternative, while mineral wool is used less often for solid slabs.
Combining floor insulation with underfloor heating installation adds a further £25 to £40 per m². This is based on typical UK installation rates from Checkatrade.
