Selecting Insulation Materials for Building Refurbishment — Cost, Application & Provider Guide
- Recommended class
- Glaswolle/Steinwolle/EPS
- Typical duration
- Planung
- Cost estimate
- 20-60 €/m²
Overview
Selecting appropriate insulation materials for building refurbishment is a critical decision that affects energy performance, fire safety, acoustic comfort, and project budgets for decades to come. Whether upgrading a Victorian terrace, retrofitting a post-war office block, or improving thermal performance in social housing, the choice between glass wool (glasswool), stone wool (mineral wool), and expanded polystyrene (EPS) depends on thermal requirements, moisture conditions, fire regulations, acoustic demands, and available cavity widths or external build-ups.
Glass wool and stone wool offer excellent thermal performance (λ-values typically 0.032-0.040 W/mK), non-combustible A1/A2 fire ratings, and good acoustic absorption, making them suitable for internal wall insulation, loft upgrades, and timber frame retrofits. EPS provides comparable thermal performance at lower cost and weight, ideal for external wall insulation systems (EWER/EWI) where fire strategy permits, though it requires careful detailing around openings and junctions. For most refurbishment projects, material costs range from £20/m² for basic EPS boards to £60/m² for high-performance stone wool slabs including fixings and vapour control layers, with planning timelines of 4-12 weeks to assess existing construction, specify compliant solutions, and coordinate with Building Control or Approved Inspectors under Building Regulations Part L and Part B.
Step-by-step
1. Survey existing building fabric and assess constraints
Conduct intrusive surveys to determine wall construction, existing insulation (if any), moisture levels, and structural condition. Use borescope cameras and thermal imaging to identify cavities, timber frame voids, or solid masonry. Measure available depth for internal insulation or check planning constraints for external insulation render thickness. Test for dampness, condensation risk, and identify any asbestos or lead paint that affects retrofit strategy. Document window reveals, service penetrations, and junction details that will require bespoke insulation cutting or fire-stopping.
2. Calculate U-value targets and condensation risk
Determine required U-values under Building Regulations Part L1B (existing dwellings, typically 0.30 W/m²K for walls, 0.16 W/m²K for roofs) or Part L2B (existing non-domestic, often 0.26 W/m²K walls). Use approved software (BR 443, CIBSE tools) to model insulation thickness needed with selected material's λ-value. Perform condensation risk analysis per BS 5250 to check interstitial condensation and specify vapour control layers or breathable membranes accordingly. For stone or glass wool, confirm fire performance meets Approved Document B requirements, especially for buildings over 18 metres or residential with cladding.
3. Select insulation type based on performance and buildability
Choose glass wool for cost-effective loft and timber frame applications where compression-fit batts simplify installation. Specify stone wool where fire resistance, acoustic performance, or higher density is required—common in party walls, steel frame infill, or external insulation under render. Select EPS for lightweight external wall insulation systems where render or cladding provides fire protection, and where lower vapour resistance aids drying. Verify product certifications (BBA, CE marking to BS EN 13162 for mineral wool, BS EN 13163 for EPS) and Environmental Product Declarations if targeting BREEAM or similar standards.
4. Procure materials and coordinate delivery logistics
Obtain quotes from insulation suppliers and distributors, comparing prices for required thicknesses, board sizes, and pack quantities. Account for cutting waste (typically 5-10%) and order vapour control layers, tapes, adhesives, and mechanical fixings as a coordinated package. Schedule deliveries to match installation programme, ensuring dry, covered storage on-site to prevent moisture ingress into mineral wool or EPS degradation from UV exposure. For large refurbishment projects, negotiate trade accounts or bulk discounts and arrange just-in-time deliveries to reduce site storage constraints and double-handling.
5. Install insulation following manufacturer guidelines and Building Regulations
For internal wall insulation, fix stone wool or glass wool batts between timber battens or within metal stud frames, ensuring continuous coverage without gaps and compressing slightly to friction-fit. Install vapour control layers on warm side, tape all joints, and service-penetration grommets. For external insulation, mechanically fix or adhesive-bond EPS or stone wool boards in brick-bond pattern, install reinforcing mesh in base coat, and apply through-coloured or painted render. Check cavity barriers, fire-stops around openings, and maintain minimum overlap distances. Inspect before covering to confirm U-value compliance and airtightness continuity.
6. Arrange Building Control inspection and document as-built performance
Notify Building Control or Approved Inspector at key hold-points (pre-insulation, pre-plasterboard for IWI, pre-render for EWI) to verify insulation type, thickness, and installation quality. Provide product datasheets, λ-values, and fire certificates for compliance file. Conduct thermographic survey post-completion to identify thermal bridging or missed areas. Update building logbook and Energy Performance Certificate (EPC) to reflect improved fabric performance. Retain warranties from insulation manufacturers and installer guarantees (typically 10-25 years for EWI systems) for future handover or asset management records.
Cost breakdown
| Glass wool batts 100mm (loft/timber frame) | £8–15/m² | Includes material only; higher density or acoustic-grade increases cost |
|---|---|---|
| Stone wool boards 120mm (IWI or cavity) | £18–28/m² | A1 non-combustible, suitable for party walls and fire-critical applications |
| EPS boards 100mm (external insulation) | £12–20/m² | Lower cost, lightweight; requires render or cladding for fire protection |
| Vapour control layer, tapes and fixings | £3–6/m² | Essential for condensation control; includes adhesive tapes and grommets |
| Mechanical fixings and adhesive (EWI) | £5–9/m² | Screw fixings with plastic washers or adhesive dabs; quantity depends on substrate |
| Render base coat, mesh and topcoat (EWI) | £15–30/m² | Silicone or acrylic render systems; labour-intensive detailing around openings |
| Delivery, waste disposal and site storage | £2–5/m² | Transport for bulk orders, skip hire for offcuts and packaging; dry storage essential |
Common pitfalls
- Failing to conduct condensation risk analysis — interstitial condensation leads to mould growth, timber decay, and insulation performance loss within 2-5 years, costing £50-150/m² to remediate.
- Using combustible insulation without adequate fire barriers in buildings over 18m — non-compliance with Approved Document B and Building Safety Act, requiring costly retrospective removal or sprinkler installation (£80-200/m²).
- Compressing mineral wool batts excessively during installation — reduces thermal performance by up to 30%, negating U-value compliance and failing Building Control sign-off.
- Inadequate detailing at junctions and service penetrations — thermal bridging and air leakage increase heat loss by 15-25%, undermining whole-building energy targets and EPC ratings.
- Ordering incorrect insulation thickness or λ-value — shortfall in thermal performance requires additional internal lining or external over-cladding, adding £20-40/m² remedial costs and delaying project completion.
- Storing glass wool or stone wool exposed to rain or groundwater — moisture absorption degrades thermal performance permanently and adds weight, making handling unsafe and material unusable (£10-25/m² replacement cost).
FAQ
- Do I need Building Regulations approval to upgrade insulation in an existing building?
- Yes, in England and Wales any work to upgrade thermal elements (walls, roofs, floors) in existing buildings falls under Building Regulations Part L1B (dwellings) or L2B (non-domestic) and requires either a Building Notice or Full Plans application to Building Control or an Approved Inspector. You must demonstrate compliance with U-value targets, condensation risk assessment, and fire safety (Part B), and the work must be inspected at key stages. Competent Person Scheme installers (e.g., CAvIA for cavity wall insulation) can self-certify certain works, but major refurbishments typically require formal approval and an updated Energy Performance Certificate upon completion.
- What is the cost difference between glass wool, stone wool and EPS for a typical refurbishment project?
- For a 100mm insulation layer, glass wool batts cost approximately £8-15/m² (material only), stone wool boards £18-28/m², and EPS boards £12-20/m². However, total installed costs vary significantly: internal wall insulation with stone wool including battens, vapour control, and plasterboard runs £60-90/m² labour-in, whereas external wall insulation with EPS, adhesive, mesh, and render totals £80-120/m² installed. Stone wool's higher material cost is often justified by superior fire performance (A1 rating) and acoustic insulation, critical for party walls and high-rise refurbishment. EPS offers the best cost-performance for external systems where render provides fire protection, but Building Safety Act restrictions on combustible materials above 18m may mandate stone wool, increasing budgets by 20-35%.
- Can I install insulation myself in a refurbishment project, or must I hire a specialist contractor?
- Technically competent individuals can self-install insulation in their own properties, but you remain responsible for Building Regulations compliance, condensation risk calculations, fire safety detailing, and arranging inspections with Building Control. Loft insulation with glass wool batts is often suitable for skilled DIY, provided you manage vapour control and avoid compressing material. Internal wall insulation or external wall insulation systems are far more complex, requiring accurate U-value modelling, airtightness detailing, render application skills, and scaffolding (for EWI), making professional contractors the safer choice. Many insurance-backed guarantees (10-25 years for EWI) are only available when installed by certified contractors, and mistakes—such as incorrect vapour barriers or fire-stopping—can cost £50-150/m² to rectify, often exceeding the labour saving from DIY.
- How do I choose between internal and external wall insulation for a refurbishment?
- External wall insulation (EWI) is preferred where possible because it eliminates thermal bridging at floor and party wall junctions, protects existing masonry from weathering, and avoids loss of internal floor area. However, EWI requires planning permission in conservation areas or for listed buildings, scaffolding access (adding £15-25/m²), and careful detailing of render or cladding systems. Internal wall insulation (IWI) is necessary where planning restricts external changes, where EWI is cost-prohibitive due to complex façades, or in flats where only certain walls are accessible. IWI reduces room sizes by 100-150mm, requires relocation of sockets and radiators, and increases condensation risk if vapour control is poorly executed. For typical solid-wall Victorian terraces, EWI costs £80-120/m² installed vs. £60-90/m² for IWI, but EWI delivers better whole-building performance and durability over 30+ year lifespan.
- What thickness of insulation do I need to meet current Building Regulations U-value targets?
- Under Part L1B (existing dwellings in England), refurbished walls must achieve U-values of 0.30 W/m²K or better (0.55 W/m²K where space or technical constraints apply). For glass wool or stone wool with λ = 0.035 W/mK, you need approximately 100-120mm thickness; for EPS with λ = 0.032 W/mK, 90-110mm suffices. Roof insulation targets 0.16 W/m²K, typically requiring 250-300mm of mineral wool in lofts. Always run a U-value calculation using actual product λ-values and existing construction details (solid brick, cavity, timber frame) rather than rule-of-thumb thicknesses, as thermal bridging, air gaps, and fixings affect real performance. For non-domestic buildings (Part L2B), wall targets are often 0.26 W/m²K, and more stringent standards (Passivhaus, BREEAM Excellent) may demand 200-350mm insulation with λ < 0.030 W/mK, significantly increasing material and buildability costs.
- Are there any grants or funding schemes to help with insulation costs in refurbishment projects?
- In England, the ECO4 (Energy Company Obligation) scheme funds insulation upgrades for low-income households and those in fuel poverty, covering cavity wall, loft, and solid wall insulation with minimal or no cost to eligible homeowners. The Home Upgrade Grant (HUG) and Local Authority Delivery (LAD) schemes also provide funding for off-gas properties and low-EPC homes. In Wales, the Warm Homes Programme offers similar support, and Scotland's Home Energy Scotland provides grants and interest-free loans for insulation and renewable heating. Social housing providers often access government capital funding or green finance for retrofit programmes. Commercial and non-domestic refurbishments may qualify for enhanced capital allowances or green business loans, though grants are less common. Check eligibility via the Simple Energy Advice service or contact local authorities, as schemes change annually and are often income- or EPC-rated, with typical grant values covering 50-100% of costs up to £10,000-25,000 per property.