Insulation Board Costs UK — What to Charge for Rigid Insulation Installation in 2026
Rigid insulation board is used everywhere — flat roofs, pitched roofs, solid walls, party walls, floors under screed. But pricing it correctly is tricky. Board type, thickness, application, cold bridge risk, and building regs compliance all feed into what you should be charging. This guide covers supply costs, supply-and-fit rates, Part L requirements, and the practical details that separate a profitable insulation job from a comeback.
Rigid Insulation Board Types & Supply Costs (2026)
The biggest variable in your quote is the board type. Lambda value (λ) determines how thick you need to go to hit a target U-value — the lower the lambda, the thinner the board you can specify, and the more you can charge for the space saved.
| Board type | λ (W/mK) | Typical thickness | Supply cost /m² | Best for |
|---|---|---|---|---|
| EPS (expanded polystyrene) | ~0.038 | 100mm | £5–£10 | Below slab, cavity fill, low-cost applications |
| XPS (extruded polystyrene) | ~0.034 | 100mm | £8–£14 | Under floor, inverted roofs, wet/damp conditions |
| PIR (polyisocyanurate) | ~0.022–0.023 | 90mm | £10–£18 | Flat & pitched roofs, walls — most common |
| PUR (polyurethane) | ~0.022 | 90mm | £10–£18 | Similar to PIR; check manufacturer fire rating |
| Phenolic board | ~0.018–0.020 | 70mm | £15–£25 | Space-critical solid walls, roof spaces |
| Mineral wool rigid slab | ~0.033–0.038 | 100mm | £6–£12 | Ventilated cavities, party walls, acoustic |
Supply-only costs. Prices vary by supplier, board thickness, and order volume. Trade accounts with merchants typically 15–25% below list.
Board-by-Board Breakdown
EPS — Expanded Polystyrene
The cheapest rigid option. Lambda ~0.038 W/mK means you need more thickness to hit a given U-value, but EPS is moisture-resistant, fully recyclable, and easy to cut. It's the workhorse for below-slab insulation on new builds and passive house floor build-ups where depth isn't a constraint. Less common for roofs because the thickness required cuts into floor-to-ceiling heights.
Watch out for: EPS is combustible (Euroclass E). Don't spec it where fire performance above E is required — confirm with building control on any commercial or HMO project.
XPS — Extruded Polystyrene
Slightly better lambda than EPS (~0.034 W/mK) and significantly better moisture resistance — XPS absorbs almost no water, making it the standard choice for inverted flat roofs (where the insulation sits above the waterproofing membrane and takes the weather), ground-bearing floors in flood-risk areas, and basement walls. Brands like Styrofoam and Jackodur dominate.
Watch out for: Some XPS products use high-GWP blowing agents — check if your client has a sustainability specification.
PIR — Polyisocyanurate
The most widely used rigid board in UK construction. Lambda ~0.022–0.023 W/mK means 90–100mm hits U-values that EPS needs 150–160mm to match. PIR comes with foil facings on both sides — this acts as a vapour control layer and reflects radiant heat. Celotex GA4000, Recticel Eurowall, and Quinn Therm are common brands you'll price from merchants.
Fire: PIR is combustible (Euroclass E or F depending on product) — must be covered within 7 days with plasterboard or cladding. Never leave exposed in an occupied building. Some manufacturers offer enhanced fire-rated products — always check the datasheet.
Phenolic Board (Kingspan Kooltherm)
The highest performance rigid board available. Lambda ~0.018–0.020 W/mK means 70mm phenolic can match what 120mm PIR or 160mm EPS achieves. It's the go-to for solid wall internal insulation where every millimetre of room width matters, and for roof spaces where rafter depth is fixed. It's also the most expensive — factor £15–£25/m² supply-only into your quote, and make sure you're charging for the value of space recovered.
Upselling opportunity: On a solid wall refurb where the client is worried about losing room width, phenolic vs PIR recovers 40–50mm per wall — that's a genuine selling point that justifies the premium.
Mineral Wool Rigid Slab (Rockwool RW3, Knauf DriTherm)
The only A2-rated non-combustible option in this list. Lambda ~0.033–0.038 W/mK, so performance-to-thickness is lower than PIR, but fire resistance is far superior — Euroclass A2 means it won't contribute to fire spread. Mandatory for many commercial and multi-residential applications. It's also breathable (vapour-open), making it the right choice for ventilated cavities and party walls where moisture management matters.
Supply-and-Fit Price Ranges by Application
These are realistic installed prices for 2026 — board, fixings, foil tape, vapour control layer where needed, and labour. They assume a competent insulation installer or builder working at typical commercial rates of £150–£250/day. Add margin for project management, access equipment, and waste disposal.
| Application | Typical board | Supply & fit /m² | Notes |
|---|---|---|---|
| Flat roof (warm roof, PIR above deck) | PIR 120–150mm | £25–£45 | Tapered systems cost more; include vapour barrier below |
| Pitched roof (between/over rafters) | PIR 90–120mm | £20–£35 | Counter-battening adds cost; access affects output |
| Solid wall internal (PIR + plasterboard) | PIR or phenolic 70–90mm | £35–£60 | MF framing or dot-and-dab; more cutting = slower output |
| Floor insulation (below screed) | PIR or XPS 100mm | £20–£35 | Fast to lay on clear slab; perimeter upstand detail matters |
| Party wall / acoustic | Mineral wool rigid slab | £25–£45 | A2-rated required in most scenarios; MF frame system |
Prices exclude VAT, scaffolding, finishing trades (plastering, screeding), and decoration. London and South East: add 15–25%.
Thickness vs Performance: Hitting Part L U-Values
Building Regulations Part L sets maximum U-values for new dwellings and extensions. The three critical targets for 2026 are:
- External walls: ≤0.18 W/m²K
- Ground floors: ≤0.13 W/m²K
- Roofs: ≤0.11 W/m²K
- Windows: ≤1.4 W/m²K (whole unit)
The table below shows the insulation thickness required for each board type to reach 0.18 W/m²K (wall target) and 0.11 W/m²K (roof target) in a simple construction. Real-world calculations depend on the full build-up — always use a U-value calculator or UKAS-accredited software and document the result for building control.
| Board type | λ (W/mK) | For 0.18 W/m²K wall | For 0.11 W/m²K roof |
|---|---|---|---|
| EPS | 0.038 | ~145mm | ~220mm |
| XPS | 0.034 | ~130mm | ~200mm |
| PIR | 0.022 | ~85mm | ~130mm |
| Phenolic | 0.018 | ~70mm | ~105mm |
| Mineral wool slab | 0.035 | ~135mm | ~205mm |
Indicative figures only — assumes a timber-framed or masonry wall/roof with standard build-up resistances. Use a proper U-value calculator for every project.
This table is your sales tool. When a client asks why phenolic costs more than EPS, you can show them: for a solid wall refurb, EPS needs 145mm and phenolic needs 70mm — that's 75mm of room width recovered per wall. On a 4m × 4m room with four solid walls, that's roughly 0.5m² of floor area returned to the client. At London property prices, that's worth far more than the board premium.
Labour Rates & Output
Rigid board installation is skilled work. It's not just laying boards — it's cutting accurately around joists and rafters, maintaining continuous cover, taping every joint with foil tape, and detailing around reveals, pipes, and penetrations. Gaps and cold bridges are invisible once plastered and will show up as damp patches, cold spots, or condensation complaints within a year.
Day rates: £150–£250/day for a skilled insulation installer or builder. Two-person team for flat roof work (one below, one above deck).
Output rates (solo installer):
- Flat roof PIR installation (above deck): 30–50m²/day on a clear, accessible roof
- Pitched roof between rafters: 20–35m²/day — more cuts, awkward access
- Solid wall internal (PIR + plasterboard, dot-and-dab): 15–25m²/day — window reveals, sockets, and pipe boxing slow output significantly
- Floor insulation (PIR below screed): 40–60m²/day on a clear slab with no penetrations
Always include in your quote:
- Foil tape (for all PIR/PUR joints) — budget 1 roll per 15–20m²
- Insulation fixings: 100mm insulation screws and washers for board-fixed applications
- Vapour control layer: required on warm side of insulation in most wall and roof applications — 3-layer membrane, lapped and taped
- Fire stopping: at all junctions with party walls, around service penetrations through insulated elements
- Waste disposal: PIR and PUR offcuts cannot go in a general skip in most local authority areas — check your waste carrier licence and disposal route
Cold Bridging — The Most Common Failure Mode
Cold bridging happens when a thermally conductive element — a steel fixing, a concrete lintel, a window reveal, a timber rafter, a wall tie — bypasses the insulation layer and conducts heat directly from inside to outside. The result is a cold spot on the interior surface, often below the dew point of the interior air, which means condensation and eventually mould.
Psi values (linear thermal bridges) and chi values (point thermal bridges) are now assessed in SAP calculations for new builds. But even on retrofit work where no SAP is required, cold bridges reduce real-world performance by 10–30% compared to the theoretical U-value.
Standard cold bridge solutions to build into your method statement:
- Continuous insulation: no gaps between boards, joints staggered if using two layers
- Insulated window reveals and sills: PIR or phenolic cut-to-fit into reveals, taped to main board
- Insulated fixings: use plastic-sleeved or low-conductivity fixings where boards are mechanically fixed
- Party wall junctions: return insulation 300mm onto the party wall to reduce flanking loss
- All joints taped: foil tape at every board-to-board joint and at the perimeter — both for vapour control and to prevent air movement through the insulation layer
Document your cold bridge strategy in writing before you start. If a client complains about damp or cold spots 18 months later, your job notes showing continuous cover and taped joints are your defence. If there are no notes, you have no defence.
Grant Funding: ECO4 & Great British Insulation Scheme
Government insulation grants are a significant source of insulation work for domestic contractors, especially in the retrofit sector. The two main schemes in 2026 are:
ECO4 (Energy Company Obligation 4)
Funded by energy suppliers, delivered through approved contractors. ECO4 targets low-income households — those receiving means-tested benefits, households with an EPC rating of D, E, F, or G, or those referred through local authority flex. Solid wall insulation (internal or external) receives the largest grants under ECO4 because it's the most expensive measure. To access ECO4 work you need to be PAS 2030:2019 certified (or work as a sub to a certified main contractor). Check gov.uk/apply-for-eco4 for current eligibility and supplier referral routes.
Great British Insulation Scheme (GBIS)
Covers loft insulation and cavity wall insulation for a broader range of households than ECO4 — including owner-occupiers in lower council tax bands and EPC D properties. GBIS does not cover rigid board solid wall insulation (that falls under ECO4), but it does cover blown cavity and loft top-up for properties that qualify. If you're doing any loft work alongside rigid board, check whether the customer qualifies for GBIS loft insulation at the same visit.
Grant schemes change frequently. Always check current guidance at gov.uk and with energy supplier scheme managers before quoting grant-funded work.
Fire Performance & Safety Obligations
PIR, PUR, EPS, XPS, and phenolic boards are all combustible. They must not be left exposed — building regulations and manufacturer guidance require coverage within 7 days of installation with an appropriate lining (typically 12.5mm fire-rated plasterboard for internal applications, or approved cladding for external). On roofs, the waterproofing membrane and ballast act as the covering.
Euroclass ratings matter: Mineral wool rigid slab is A2 (non-combustible, tested to EN 13501-1). PIR and phenolic are typically Euroclass E or F. On high-rise residential buildings (over 11m), the external wall system must be A2 or A1 rated — combustible insulation boards are not acceptable in those build-ups without an A2-rated cladding system that has full EWS1 sign-off.
Waste disposal: PIR and PUR offcuts contain isocyanates and are classified as hazardous waste by some local authorities. Don't tip offcuts into a general builder's skip without checking. Use a licensed waste carrier with the appropriate waste code and keep your waste transfer notes on file.
Before you start any insulation job on a building with cladding already present, check whether an EWS1 form is required and whether the existing build-up is compliant. Retrofitting combustible insulation behind non-compliant cladding creates liability that outlasts the job.
Quoting Rigid Insulation Jobs: Key Checklist
Before you submit a price, make sure you've covered:
- Board specification confirmed: type, thickness, lambda value, and calculated U-value documented
- Building Regs compliance: does the spec hit Part L targets? Will building control inspect? Do you need a U-value certificate?
- Cold bridge strategy: window reveals, junctions, fixings — all noted in the method statement
- Fire rating confirmed: correct Euroclass for the building type and height; cover-up timeline agreed
- Access included: scaffold, MEWP, or working-at-height equipment costs in the quote
- Ancillaries priced: foil tape, fixings, VCL, fire stopping, perimeter detail materials
- Waste disposal allowed for: licensed carrier, correct waste code, transfer notes
- Defects and comeback risk assessed: if the substrate is poor (damp masonry, uneven deck), call it out in writing before you start
Rigid board insulation is one of the highest-value upgrades a contractor can deliver — but it's also one of the easiest to get wrong quietly. A gap in the insulation layer, an untaped joint, or an uninsulated reveal costs nothing to fix before the plasterboard goes on and thousands to investigate afterwards. Price the job properly, specify the right board, document the U-value, and tape every joint. That's the job.
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