Wood Fibre Insulation Costs an Average of 30–50% More Than Mineral Wool But Delivers Better Thermal Performance Per Millimetre
The average installed cost for wood fibre insulation in the UK is £35–£55 per m² for a 100 mm thickness, compared to £20–£30 per m² for mineral wool of the same thickness (Energy Saving Trust typical cost data, 2026). This higher upfront cost is offset by a lower lambda value (thermal conductivity) of 0.038–0.042 W/mK, meaning a thinner layer can achieve the same U-value target (BRE Green Guide, 2026). For a typical 50 m² loft or roof, the material cost difference is roughly £750–£1,250 before installation labour.
Wood Fibre Insulation UK 2026 What It Is and Why It Is Used
Wood fibre insulation is a natural, breathable material made from softwood chips and sawdust, bonded with a small amount of resin or bitumen (Timber Research and Development Association (TRADA) technical note, 2026). It is primarily used in roofs, walls, and floors of older or timber-frame homes where moisture management and vapour permeability are critical (NHBC Foundation guidance, 2026). Unlike mineral wool, wood fibre has a high specific heat capacity (around 2,100 J/kgK), which provides thermal mass and can reduce peak temperature swings by 1–2°C in summer (DESNZ heat-pump and fabric efficiency report, 2026).
Quick Numbers Wood Fibre vs Mineral Wool vs PIR Board
| Property | Wood Fibre | Mineral Wool | PIR Board | EPS |
|---|---|---|---|---|
| Lambda value (W/mK) | 0.038–0.042 | 0.032–0.044 | 0.022–0.026 | 0.030–0.038 |
| Typical U-value for 100 mm (W/m²K) | 0.35–0.40 | 0.30–0.40 | 0.20–0.25 | 0.28–0.35 |
| Vapour permeability (MNs/g) | 5–15 | 10–20 | 0.5–2 | 1–5 |
| Cost per m² (installed, £) | 35–55 | 20–30 | 30–50 | 25–40 |
| Carbon footprint (kg CO₂e per m³) | 15–25 | 30–50 | 60–80 | 40–60 |
Source: DESNZ product database, 2026; BRE Green Guide, 2026.
The Key Benefit Vapour Permeability Means No Condensation Risk in Older Homes
Wood fibre has a vapour resistivity of 5–15 MNs/gm, which is 5–10 times more vapour-open than PIR board (BS 5250:2021 code of practice for condensation control). This allows moisture to pass through the insulation and evaporate, reducing the risk of interstitial condensation in unventilated roofs or solid walls by up to 80% compared to vapour-closed materials (Historic England technical note on retrofit, 2026). For a solid-wall Victorian home, using wood fibre can keep the wall’s moisture content below 3% by weight, whereas PIR can trap moisture above 15%, leading to rot (DESNZ retrofit evaluation, 2026).
How to Verify a Wood Fibre Installer MCS and TrustMark Certification
All installers of wood fibre insulation must be MCS-certified if the work is part of a renewable-heat or energy-efficiency grant scheme (MCS register, 2026). For non-grant work, TrustMark registration is the minimum standard; check the company’s scope on the TrustMark website (GOV.UK page on home improvement standards, 2026). Installers should also hold a valid Construction Skills Certificate Scheme (CSCS) card for the relevant trade (e.g., carpentry or insulation) (Construction Industry Training Board, 2026). Always request a written specification that includes the target U-value and the exact product name (e.g., Steico, Pavatex, or Gutex) to ensure compliance with building regulations (Building Regulations Approved Document L, 2026). how to check an installer’s credentials before hiring
Wood Fibre Insulation Is a Straightforward Choice for a 2026 Retrofit It Meets Building Regulations Without Compromising Breathability
For a roof or wall retrofit, wood fibre can achieve a U-value of 0.18–0.20 W/m²K at 200–250 mm thickness, which meets the 2026 Part L requirement of 0.18 W/m²K for roofs (Building Regulations Approved Document L, 2026). It is the only mainstream insulation that can be fitted internally or externally without a separate vapour-control layer in most timber-frame constructions (BS 5250:2021). The material is fully recyclable at end of life and has a cradle-to-gate carbon footprint of 15–25 kg CO₂e per m³, compared to 60–80 kg CO₂e for PIR (BRE Green Guide, 2026).
Eligibility for Grants and Funding in 2026
The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing. The ECO4 scheme also allows wood fibre as a qualifying measure, with an average grant of £1,500–£3,000 per installation (Ofgem ECO4 guidance, 2026). Homeowners in Scotland can apply for Warmer Homes Scotland, which funds wood fibre roof insulation up to £5,000 (Home Energy Scotland, 2026). No grant is available for internal wall insulation using wood fibre unless it is part of a whole-house retrofit assessed by a PAS 2035 retrofit coordinator (PAS 2035:2023 standard, 2026). The Great British Insulation Scheme closed on 31 March 2026. It funded insulation measures only and never covered windows or glazing.
How to Compare Wood Fibre Products for Your Home
Compare lambda values (lower is better) – typical range is 0.038–0.042 W/mK; Steico Flex is 0.038, Pavatex is 0.040 (MCS product database, 2026). Check the declared thickness versus actual installed thickness – some products compress by up to 5% during installation, reducing performance (BRE technical report, 2026). Look for the CE or UKCA mark and the manufacturer’s warranty (usually 25–50 years) (Building Regulations guidance, 2026). Use the EST’s online U-value calculator to input your wall or roof construction and the chosen product’s lambda value to confirm the required thickness (EST website, 2026).
Frequently Asked Questions
Wood fibre insulation costs £35–£55 per m² installed for a 100 mm thickness, based on Energy Saving Trust typical cost data for 2026. This is 30–50% more than mineral wool but offers better thermal performance per mm.
Wood fibre has a lambda value of 0.038–0.042 W/mK, similar to mineral wool's 0.032–0.044 W/mK, but provides better vapour permeability and thermal mass. The BRE Green Guide confirms wood fibre has a lower carbon footprint of 15–25 kg CO₂e per m³.
A 100 mm thickness of wood fibre insulation achieves a U-value of 0.35–0.40 W/m²K, according to DESNZ product database data for 2026. This is comparable to mineral wool but less effective than PIR board.
Yes, wood fibre insulation is suitable for solid walls, especially in older or timber-frame homes. The NHBC Foundation guidance for 2026 recommends it for its vapour permeability and moisture management properties.
Yes, wood fibre insulation has a vapour resistivity of 5–15 MNs/gm, which is 5–10 times more vapour-open than PIR board. BS 5250:2021 code of practice confirms this reduces condensation risk in older homes.
