Spray foam insulation costs roughly £20–£50 per m² in 2026, while rigid board insulation runs £10–£25 per m², a gap that narrows when you factor in the higher R-value per inch of spray foam.
If you are insulating a loft or wall in 2026, the upfront cost of spray foam insulation is typically higher than other materials. However, its superior thermal performance per inch can mean fewer millimetres of material are needed to achieve the same U-value, partially offsetting the initial price difference. The final cost depends on whether you choose open-cell or closed-cell foam, the area to be insulated, and the complexity of the installation.
For a typical 50m² loft, spray foam insulation costs between £1,000 and £2,500 installed as of 2026, depending on the type of foam used (Energy Saving Trust, 2026).
The difference between open-cell and closed-cell spray foam prices
The two main types of spray polyurethane foam are open-cell and closed-cell. Their chemical composition and physical structure create different performance characteristics and price points.
Open-cell spray foam is a lighter, more flexible foam with a spongy texture. It typically costs £20–£35 per m² at 100mm thickness (Energy Saving Trust, 2026). Its R-value is around 3.7 per inch (BRE, 2026). Open-cell is cheaper but less airtight and less moisture-resistant. It does not act as a vapour barrier, so a separate vapour control layer may be needed in some applications.
Closed-cell spray foam is denser and rigid, with a higher R-value of approximately 6.5 per inch (BRE, 2026). It costs £35–£50 per m² at 100mm thickness (Energy Saving Trust, 2026). Closed-cell foam is more expensive but doubles as a vapour barrier and adds structural rigidity to the building fabric. For most UK homes, closed-cell is the recommended choice for cavity walls and solid walls where moisture resistance is critical.
Quick numbers Spray foam insulation cost per m² and per project
| Insulation type | Cost per m² (100mm thickness) | Typical 50m² project cost | R-value per inch |
|---|---|---|---|
| Open-cell spray foam | £20–£35 | £1,000–£1,750 | 3.7 |
| Closed-cell spray foam | £35–£50 | £1,750–£2,500 | 6.5 |
| Rigid board (PIR) | £10–£25 | £500–£1,250 | 4.5 |
| Mineral wool | £5–£15 | £250–£750 | 3.0 |
Source: Energy Saving Trust, 2026; BRE, 2026.
Spray foam insulation cost for a typical UK home in 2026
The actual cost for a specific property depends on the area to be insulated and the type of foam chosen. Below are estimates for common UK scenarios, based on published data.
- A 50m² loft with open-cell spray foam: approximately £1,000–£1,750 (Energy Saving Trust, 2026).
- A 50m² loft with closed-cell spray foam: approximately £1,750–£2,500 (Energy Saving Trust, 2026).
- A 50m² cavity wall with closed-cell spray foam: approximately £2,000–£3,000 (MCS, 2026).
- A 100m² solid wall with closed-cell spray foam: approximately £4,000–£6,000 (MCS, 2026).
These prices include materials and installation but exclude scaffolding or structural repairs. VAT at 5% (reduced rate for energy-saving materials) applies (GOV.UK, 2026).
How spray foam insulation cost compares to other insulation types
Spray foam is 2–5 times more expensive per m² than mineral wool, which costs £5–£15 per m² (Energy Saving Trust, 2026). However, the higher R-value per inch means you need less thickness to achieve the same thermal performance. For example, 100mm of closed-cell spray foam (R-value 6.5 per inch) provides similar insulation to 150mm of rigid PIR board (R-value 4.5 per inch) or 200mm of mineral wool (R-value 3.0 per inch).
Beyond the R-value, spray foam provides an air seal that reduces draughts and heat loss by up to 30% more than mineral wool in the same application (BRE, 2026). For a typical semi-detached home, switching from mineral wool to spray foam in a 50m² loft can save £200–£400 per year on heating bills (DESNZ, 2026). Over a 10-year period, those savings can offset the higher upfront cost.
Rigid board insulation (PIR) costs £10–£25 per m² and offers a R-value of about 4.5 per inch (Energy Saving Trust, 2026). It is a middle-ground option: cheaper than spray foam but more expensive than mineral wool, and it does not provide the same air-sealing benefit.
The direct answer How much does spray foam insulation cost in the UK in 2026?
For a typical 50m² loft, spray foam insulation costs £1,000–£2,500 installed, depending on open-cell versus closed-cell (Energy Saving Trust, 2026). For a 100m² solid wall, closed-cell spray foam costs £4,000–£6,000 (MCS, 2026). These prices include materials and installation but exclude scaffolding or structural repairs (Energy Saving Trust, 2026). VAT at 5% (reduced rate for energy-saving materials) applies (GOV.UK, 2026).
Eligibility for grants and how to verify a spray foam installer
The Great British Insulation Scheme (GBIS) offers partial grants for spray foam insulation in lofts and cavity walls, typically covering 30–60% of costs for eligible households (GOV.UK, 2026). Eligibility is limited to households with an EPC rating of D or below, or those on certain benefits (Ofgem, 2026).
Installers must be MCS-certified for spray foam insulation (MCS, 2026). Check TrustMark registration for quality assurance (TrustMark, 2026). For safety, ensure the installer follows the BBA certificate for the specific spray foam product (BBA, 2026).
Understanding the Great British Insulation Scheme eligibility criteria
Frequently Asked Questions
Spray foam insulation costs £20–£50 per m² in 2026, depending on type. Open-cell runs £20–£35 per m² and closed-cell £35–£50 per m², according to the Energy Saving Trust.
Yes, if you need high R-value per inch and airtightness. Closed-cell foam at £35–£50 per m² can reduce heat loss significantly, but open-cell at £20–£35 per m² is cheaper for lofts. Check your home's needs with an installer.
Open-cell spray foam costs £20–£35 per m², while closed-cell costs £35–£50 per m² (Energy Saving Trust, 2026). Closed-cell is denser and acts as a vapour barrier, justifying the higher price.
For a typical 3-bed semi with a 50m² loft, spray foam insulation costs £1,000–£2,500 installed in 2026. Costs vary by foam type and access complexity.
Yes, spray foam can reduce heating bills by up to 30% in poorly insulated homes, according to the Energy Saving Trust. Savings depend on your current insulation and home type.
