Spray Foam Insulation Costs UK — What to Charge for Open and Closed Cell Foam in 2026

Open Cell vs Closed Cell: The Fundamental Difference

Spray polyurethane foam (SPF) comes in two chemically distinct formulations. Choosing the wrong type for a given application is one of the most common specification errors in the trade.

Open Cell Foam

Open cell foam has a low density — typically 8–12 kg/m³ — and a soft, flexible texture when cured. The cell structure is deliberately ruptured during expansion, leaving an interconnected network of open cells. This makes open cell foam vapour-permeable: moisture vapour can pass through the material, which is an advantage in some applications and a critical weakness in others. Thermal conductivity is around 0.038 W/mK. Open cell foam is significantly cheaper than closed cell and expands to a much greater volume per kilogram of chemical applied — typically 100:1 expansion ratio or more. It is well suited to internal partition walls (for sound insulation), internal stud wall applications and some loft rafter configurations where vapour permeability is acceptable. Its softness also makes it easy to trim flush with rafter faces using a bread knife or hot wire cutter.

Closed Cell Foam

Closed cell foam has a high density — typically 30–50 kg/m³ — and a rigid, structural character when cured. The cells remain intact and sealed, trapping the blowing agent gas inside, which gives closed cell foam its superior thermal performance: conductivity of 0.022–0.028 W/mK, roughly half that of open cell. To achieve the same U-value target, closed cell foam can be applied at half the thickness of open cell — a decisive advantage where rafter or substrate depth is limited. Closed cell foam also acts as a moisture barrier, resisting liquid water and water vapour transmission. It bonds tenaciously to most substrates including timber, steel, concrete and masonry, and adds meaningful structural stiffness to a rafter assembly. These properties make it the correct choice for roof applications, flat roof undersides, cold store construction, metal building insulation and any situation where a vapour control layer is required.

Spray Foam Insulation Costs at a Glance (2026)

All prices are supply and apply (materials plus labour) for a 2-man team, based on 2026 UK market rates. Prices vary with access difficulty, area size, foam depth required and regional labour costs. Larger areas reduce the per-m² cost; awkward access and small, broken-up areas increase it.

What Drives the Cost

Spray foam pricing is more variable than most insulation products because so many site-specific factors affect how long the job takes and how much chemical is consumed.

• Foam depth (U-value target): The biggest single cost driver. Chemical consumption is directly proportional to the volume of foam applied. A 50mm closed cell application to achieve a U-value of around 0.35 W/m²K costs roughly half what a 100mm application costs. Always specify the target U-value and the resulting foam depth in your quote — this is the parameter that defines what is being priced.
• Substrate type: Foam adheres differently to timber, steel, concrete and masonry. Steel and concrete substrates in cold or damp conditions may require a primer or surface preparation step before foam can be applied. Masonry can be dusty or contaminated, requiring blowing out or brushing down. Timber in old loft spaces is often contaminated with decades of dust and fibrous loft insulation debris, which needs clearing before spray begins.
• Access and working conditions: Loft spaces are the most physically demanding spray foam environment. A pitch that requires the operatives to work flat on their backs between rafters 400mm on centre, in a 600mm-high eaves section with no boarding, takes substantially longer than an open loft with full standing height. Scaffold access for external flat roofs or metal buildings adds cost. Price access difficulty into your day rate, not your per-m² rate.
• Masking and preparation: Every surface that must not receive foam — tank platforms, pipework, electrical cables, water tanks, purlin ties — requires masking with polythene sheet and tape before application. In a typical 3-bed semi loft this can take 1–2 hours of a 2-man team's time before any foam is applied.
• Area size: Chemical rigs have a minimum viable heat-up and preparation time regardless of how much foam is applied. Small areas (under 20m²) carry a minimum mobilisation cost — typically £300–£500 — that prices them at a higher per-m² rate than larger areas.

Application Equipment and Overhead Costs

Spray foam is not a product you can apply with off-the-shelf tools. The chemical components — the A-side (isocyanate) and B-side (polyol blend) — must be precisely metered, heated to the correct temperature range and mixed at the spray gun tip at an exact 1:1 ratio. Too cold, too hot or off-ratio and the foam will either not cure properly, produce excessive shrinkage or generate a tacky, under-reacted surface that off-gasses isocyanate into the building. This is why the equipment specification matters and why you should treat rig costs as a real overhead.

• Full spray rig (proportioner pump, drum heaters, heated hose, spray gun): New cost £15,000–£30,000 depending on whether you opt for a pneumatic proportioner or an electric/hydraulic unit. A pneumatic proportioner (e.g. Graco Reactor or PMC) at the lower end of the price range is adequate for residential work up to medium scale. Electric proportioners with digital ratio control are more consistent and suit contractors doing regular commercial volume.
• Rig rental: Several equipment hire companies offer spray foam rigs on a daily or weekly basis at £300–£600 per day. If you are doing fewer than 4–5 spray foam jobs per month, rental is likely more cost-effective than ownership — particularly for a new entrant to the market who wants to test demand before committing capital.
• PPE and respiratory protection: Isocyanate is a Category 1A respiratory sensitiser. HSE requires supplied-air breathing apparatus (SABA) or air-fed respirators during spray operations. Full-face air-fed hood systems cost £500–£1,500 per operative. Factor in the cost of air compressor supply or airline airline connections. Chemical-resistant coveralls, gloves and boots are single-use consumables and must be budgeted per job.
• Chemical drums: A 200-litre set (one drum A-side, one drum B-side) covers roughly 20–25m² at 100mm closed cell or 50–70m² at 100mm open cell. Chemical cost per drum set runs £400–£800 depending on product and supplier.

Labour Rates and Team Composition

Spray foam insulation is a 2-man operation. The spray operative handles the gun and controls foam application; the labourer assists with masking, drum changeovers, monitoring foam quality and ensuring ventilation is maintained. Working alone is not safe practice: the isocyanate hazard requires a second person present who can respond if the operative is overcome.

• Spray operative (lead installer): £200–£300 per day. An experienced operative who can also survey, specify foam depth and operate and maintain the rig commands the upper end of this range.
• Labourer / second operative: £120–£160 per day.

A typical 3-bed semi loft (50–70m² of rafter area at 100mm open cell) takes a 2-man team a full day including rig set-up, masking, application and pack-down. That gives a combined labour cost of £320–£460 for the day. Add chemical, PPE consumables and rig overhead and you arrive at a job cost of £1,000–£1,800 before profit margin — consistent with market prices of £1,500–£4,000 for this application, with the variation driven by access difficulty, foam depth and regional labour costs.

BBA and KIWA Certification: Why It Matters

Not all spray foam products on the UK market carry third-party certification. The British Board of Agrément (BBA) and KIWA are the two principal certification bodies that assess spray foam products against defined performance criteria and issue Agrément Certificates. These certificates confirm that a product has been independently tested, that the performance claims are substantiated, and that there is a defined specification for how the product must be applied.

For a spray foam insulation contractor, BBA or KIWA certification matters in three practical contexts:

• Building control acceptance: Local authority building control officers are more likely to approve a spray foam installation specified using a BBA-certified product with a defined scope of use than one using an uncertified product with manufacturer-only data sheets.
• Insurance recognition: Some home insurers and specialist retrofit insurers require BBA or KIWA certification as a condition of recognising a spray foam installation within the property's cover. Using an uncertified product leaves you exposed if a claim arises.
• Commercial and public sector tendering: Many commercial clients and housing associations specify BBA-certified products in their tender documents. Without this, you cannot bid for those contracts.

Always name the specific product and its certification status on your quote. A quote that states “spray foam insulation applied to rafters” is not a specification. A quote that states “Icynene LD-C-50® open cell spray foam, BBA Certificate 10/4742, applied at 100mm to rafter underfaces” is.

ECO4 Funding: Spray Foam Is No Longer Eligible

This is a point of significant confusion in the market. Spray foam insulation was removed from ECO4 eligibility in most circumstances in 2023, following concerns raised by RICS surveyors, mortgage lenders and consumer protection bodies about the mortgage implications for homeowners. The decision by Ofgem and DESNZ (the Department for Energy Security and Net Zero) was that the mortgage risk to the homeowner outweighed the thermal benefit in the scheme context, particularly for loft and roof void applications.

If you are approached by a managing agent or energy broker claiming that spray foam is ECO4-eligible and that they can secure funding for loft spray jobs, treat this with scepticism. Verify directly via the Ofgem ECO4 guidance documentation before committing to any ECO4-funded spray foam project. Proceeding with an ineligible measure under a grant scheme exposes your business to clawback and potential regulatory action.

The Great British Insulation Scheme (GBIS) similarly does not routinely fund spray foam in roof voids. Cavity wall spray foam occupies a greyer area — confirm current eligibility with the managing agent and your TrustMark registration body before pricing any grant-funded cavity application.

Thermal Performance: The Numbers Behind the Claims

Understanding the thermal performance difference between open and closed cell foam matters when you are specifying depth and justifying your quote to a technically informed client.

• Open cell foam at λ = 0.038 W/mK requires approximately 150mm to achieve a U-value of around 0.25 W/m²K at rafter level (accounting for the thermal bridging effect of the rafters themselves). At 100mm, open cell typically achieves 0.35–0.40 W/m²K — acceptable for Part L compliance but not optimal.
• Closed cell foam at λ = 0.024 W/mK achieves the same 0.25 W/m²K target at approximately 80mm. This is why closed cell is specified where rafter depth is limited — on a Victorian property with 100mm×50mm rafters, 80mm of closed cell leaves 20mm of ventilation gap, whereas 150mm of open cell is physically impossible without losing the ventilation gap entirely.

Always carry out a U-value calculation for every spray foam quote and include the output in the written quote. For loft rafter applications, the calculation must account for the linear thermal bridge of the rafters (typically using ISO 10211 zone method or BRE IP 1/06). If you are not comfortable producing U-value calculations in-house, use an online tool such as the BRE U-value calculator or commission a calculation from a thermal modeller — it costs £50–£150 and protects you in any Building Regulations compliance dispute.

How to Quote Spray Foam Insulation

A professional spray foam quote has five components. Miss any one of them and you are creating a dispute risk.

1. Detailed site survey: Measure the actual rafter or substrate area to be treated. Measure rafter depth and centres. Assess access difficulty (loft hatch size, ridge height, boarding). Note any contamination, existing insulation to remove, or structural concerns. Photograph the loft before any work begins.
2. Product specification: Name the foam product, manufacturer, BBA or KIWA certificate number, foam type (open or closed cell), and the specified application depth. This is your contractual commitment to what will be delivered.
3. U-value calculation: State the existing U-value of the roof element (uninsulated rafters in a cold loft are typically 2.5–3.0 W/m²K), the proposed foam depth, and the achieved U-value. Confirm compliance with Part L of the Building Regulations where applicable.
4. Mortgage and insurance disclaimer: Include a clearly worded section that states the mortgage and insurance implications of spray foam in the roof void. Require the client to initial this section specifically, not just sign the bottom of the quote.
5. Exclusions: Be explicit about what is not included — removal of existing loft insulation, electrical or plumbing alterations, reinstatement of loft boarding, any structural repairs identified during survey. Spray foam surveys sometimes reveal roof timber defects that must be rectified before foam is applied. Do not apply foam over defective timbers and do not include structural repairs in your foam price unless you have separately scoped and priced that work.

Where Spray Foam Jobs Come From

The referral network for insulation contractors who do spray foam work is different from most other insulation products. Because spray foam has specialist applications — flat roofs, cold stores, agricultural buildings, metal cladding systems — as well as the residential retrofit market, leads arrive from a wide range of sources.

• Energy assessors and retrofit coordinators: Particularly for loft and rafter applications. Even though spray foam is no longer ECO4-eligible, energy assessors still encounter clients who want the warm roof option and refer them to installers who can specify it correctly. Building a relationship with local retrofit coordinators and assessors is one of the highest-value referral channels for a residential spray foam contractor.
• Mortgage brokers (paradoxically): Some mortgage brokers who advise clients on properties that already have spray foam will refer those clients to removal specialists or to contractors who can provide a RICS-acceptable report on the installation's quality. This is a growing niche.
• Roofing contractors: Roofers who replace flat roofs or repair pitched roofs regularly encounter opportunities to upsell insulation as part of the works. Many pass these to specialist spray foam contractors as a sub-contract or refer them directly.
• Agricultural and commercial direct: Farmers insulating steel portal frame buildings, warehouse owners upgrading cold stores, and food processing facilities with hygiene-grade closed cell requirements — these clients typically find you via Google search or direct referral and convert at higher average values than residential.