A bare one-and-a-half-brick solid wall — 317.5mm of brickwork (the nominal 215 + 102.5 brick dimensions; a little more if built as separate leaves with a collar joint) — has a U-value of roughly 1.5–1.7 W/m²K, with soft, older bricks at the worse end. That is far above any current standard, which is why these walls are almost always insulated: an 80mm PIR internal lining reaches about 0.24, and external insulation gets there without losing internal space. Internal insulation cools the brickwork and moves the dew point, so run the free ISO 13788 condensation screening before fixing a spec. Open the build-up below pre-filled and add your lining.
Every layer editable · live U-value · Part L & Future Homes Standard targets · free PDF report
The build-up (outside → inside)
- 317.5mm solid brickwork (one-and-a-half brick)
- 13mm dense plaster
Typical U-values for this construction
| Specification | U-value (W/m²K) | Notes |
|---|---|---|
| Bare 1½-brick wall (uninsulated) | ≈ 1.5–1.7 | The starting point — needs insulating |
| + 80mm PIR internal insulation (IWI) | ≈ 0.24 | The usual retrofit; see the solid-brick + internal insulation page |
| + external insulation (EWI) | ≈ 0.26 | Keeps internal space; see the solid-brick + external insulation page |
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
Almost nothing moves a bare solid wall except its thickness and brick density — soft, low-density bricks conduct a little less but weather worse. The only real fix is insulation, and on a solid wall that is a moisture decision as much as a thermal one: model the lining in U-Monkey and use its free ISO 13788 condensation screening before you commit. For unusual or historic fabric, get a full hygrothermal assessment.
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 £35 +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 one-and-a-half-brick (317.5mm) solid wall?
A bare one-and-a-half-brick solid wall — 317.5mm of brickwork (the nominal 215 + 102.5 brick dimensions; a little more if built as separate leaves with a collar joint) — has a U-value of roughly 1.5–1.7 W/m²K, with soft, older bricks at the worse end. That is far above any current standard, which is why these walls are almost always insulated: an 80mm PIR internal lining reaches about 0.24, and external insulation gets there without losing internal space. Internal insulation cools the brickwork and moves the dew point, so run the free ISO 13788 condensation screening before fixing a spec. Open the build-up below pre-filled and add your lining.
What is the U-value of a 317.5mm (one-and-a-half-brick) solid wall?
Bare, roughly 1.5–1.7 W/m²K — 317.5mm is the nominal 215 + 102.5 brick dimensions. It needs internal or external insulation to approach the 0.30 renovation target; about 80mm of internal PIR brings a typical wall to around 0.24. Model yours free in U-Monkey and run the condensation check first.
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
- U-value of a solid wall with external 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
- Flat roof insulation thickness — about 150mm PIR for 0.15, 140mm for 0.16
- 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, and why two calculators can give different answers for the same wall.