External wall insulation with 90mm grey EPS takes a 215mm solid brick wall from roughly 1.6–1.7 W/m²K to about 0.30 — the renovation target — and 110mm reaches about 0.25. EWI keeps the brick warm (kind to the wall and the dew point) at the cost of external appearance and detailing at eaves and openings.
Every layer editable · live U-value · Part L & Future Homes Standard targets · free PDF report
The build-up (outside → inside)
- Thin-coat render
- 90–110mm grey EPS
- 215mm solid brick
- Internal plaster
Typical U-values for this construction
| Specification | U-value (W/m²K) | Notes |
|---|---|---|
| 90mm grey EPS + render | ≈ 0.30 | Typical ECO-scheme spec |
| 110mm grey EPS + render | ≈ 0.25 | Comfortable pass |
Figures computed with the BS EN ISO 6946 combined method (bridging included) using BR 443 conventional lambda values — indicative for the generic build-up shown. Your products, thicknesses and (for floors) footprint will move the number: that's what the calculator is for.
What changes the number
Board thickness and lambda (grey EPS 0.031 vs white 0.038) set the number. Unlike IWI, EWI keeps the masonry warm, so condensation risk is generally lower — but junctions, DPC level and fire classification of the system need real attention.
Next: check the junctions
A U-value covers the flat area of an element — but heat also escapes where elements meet, and at modern U-values those junctions can be 20–30% of a dwelling's fabric heat loss. Now you know your U-values, model the junctions with the free ΨMonkey psi value calculator (no subscription; PDF reports £25 +VAT):
Or read thermal bridging explained to see how junction Ψ-values feed your SAP calculation.
Frequently asked questions
What is the U-value of a solid wall with external insulation?
External wall insulation with 90mm grey EPS takes a 215mm solid brick wall from roughly 1.6–1.7 W/m²K to about 0.30 — the renovation target — and 110mm reaches about 0.25. EWI keeps the brick warm (kind to the wall and the dew point) at the cost of external appearance and detailing at eaves and openings.
EWI or IWI for a solid wall?
Thermally they can reach similar U-values. EWI keeps the wall warm and the rooms full-size but changes the outside and costs more; IWI is room-by-room and cheaper but eats space and needs careful moisture design. Model both in U-Monkey and run the condensation check on the IWI option.
Is this calculator free?
Yes — building the element, reading the U-value, the compliance targets (including the Future Homes Standard) and the condensation-risk screening check are all free in your browser, and the Building Control-ready PDF report is free too. No sign-up.
Does it follow the official calculation method?
Yes — the combined method of BS EN ISO 6946:2017 with BR 443 conventions, including timber bridging and air-gap corrections, ISO 13370 for ground and suspended floors, and ISO 13788 for the condensation screening check.
Other common build-ups
- U-value of a cavity wall with full-fill insulation
- U-value of a cavity wall with PIR partial-fill insulation
- U-value of a timber frame wall
- U-value of a solid brick wall with internal insulation
- What is the U-value of an uninsulated cavity wall?
- U-value of 270mm loft insulation
- U-value of insulation between rafters (loft conversion)
- U-value of a warm flat roof
- How much insulation does a flat roof need?
- U-value of an insulated concrete ground floor
- U-value of an insulated suspended timber floor
- U-value of a beam and block floor with PIR
Different build-up? See the full wall U-value calculator, or start from scratch in the main U-value calculator.
Need the wider compliance picture? U-values feed straight into SAP calculations — or let our New Build Compliance Pack handle the lot. Background reading: what U-values actually are.