What is external wall insulation?
External wall insulation (EWI) adds an insulating layer to the outside of your external walls, finished with render or cladding. It’s ideal for solid‑wall properties (often pre‑1920s) where cavity wall insulation isn’t suitable. Benefits include lower heat loss, improved comfort and EPC rating, and a refreshed façade.
Quick start: Not sure where to begin? Use our short questionnaire in the cost calculator and get a tailored ball‑park estimate in minutes.
Typical external wall insulation cost (UK)
In 2025, most UK homeowners can expect £90 – £180 per m² including materials and labour, with whole‑house projects ranging from ~£6,000 for a small flat to £25,000 – £30,000+ for a large detached, depending on specification, access and finish.
£90 – £180 / m²
Varies with insulation type (EPS, mineral wool, PIR), thickness, render system and detailing.
~£10k – £18k
Three‑bed semi with mid‑range silicone render and standard access.
~£15k – £30k+
Larger wall area, more scaffolding and elevations; premium finishes push costs higher.
External wall insulation cost by property type
Note: These are guideline figures for planning only. For a personalised projection, use our EWI Cost Calculator or request a survey.
What changes the price?
Size & property type
The primary driver is total external wall area. Multi‑storey, detached or complex elevations mean more material, fixings, mesh and labour.
Condition & prep work
Repairs to cracked brickwork, removing old render, addressing damp, replacing sills or trims will add to pre‑installation costs.
Insulation material & thickness
EPS is typically the most cost‑effective; mineral wool offers superior fire and acoustic performance; PIR provides high thermal efficiency at lower thickness.
Finish type
Silicone render is popular for its durability and water repellence; decorative cladding or brick‑slips increase cost.
Access & scaffolding
Gables, dormers and restricted access require more scaffolding and labour, increasing installation time and cost.
Location & permissions
London/South East labour rates trend higher; conservation areas or listed buildings may require specific systems and approvals.
Savings, payback & non‑monetary benefits
- Annual bill savings: often in the range of £140–£700 for typical homes; larger detached homes may save more.
- Payback: depends on energy prices and specification; plan for a long‑term horizon and comfort benefits.
- Comfort & health: fewer cold spots and condensation when detailing is done correctly.
- Asset value: improved EPC rating can support resale value and mortgageability.
Tip: Combine EWI with other works (guttering, roofline, solar PV) to share scaffolding costs and reduce disruption.
How to budget (Step‑by‑Step)
- Measure external wall area (height × perimeter minus windows/doors).
- Pick a system: insulation type + thickness + render/cladding finish.
- Use £120 – £180/m² as a planning range, then refine via quotes.
- Add 10–20% contingency for prep work, access and detailing.
- Check if grants or local schemes reduce net cost.
- Get 3+ detailed quotes from certified installers; compare like‑for‑like.
- Use the EWI Cost Calculator to sanity‑check quotes.
Choosing materials & specification
When comparing proposals, ask for clarity on:
- Insulation board type (EPS, Mineral Wool, PIR, Wood Fibre) and thickness (target U‑value).
- Adhesive/base coat, mesh weight, fixings and brand system compatibility.
- Render system (e.g., silicone/coloured render) or cladding/brick‑slips.
- Scaffolding, waste removal, weather contingencies, warranties and certifications.
- Elevations included (front, rear, gables), window trims/sills and services relocation (pipes, cables, lights).
Ways to reduce cost (Without cutting corners)
- Schedule during off‑peak periods or combine with other external works to share access costs.
- Choose robust mid‑range finishes; avoid ultra‑premium cladding where budget is tight.
- Request an itemised breakdown and discuss value‑engineering options with your installer.
- Insist on quality control and certification to avoid expensive remediation later.
External wall insulation cost — FAQs
It’s possible but less effective and can create thermal bridging. Whole‑house coverage offers better performance and visual consistency.
Yes—detailing around openings is labour‑intensive and requires trims or extended sills. It improves performance and finish quality.
Usually not, but conservation areas/listed buildings may require approval. Always check with your local authority.
Mineral wool can offer superior fire and acoustic performance. EPS is more budget‑friendly; PIR achieves lower U‑values at reduced thickness. The best choice depends on your goals and budget.