U-value of a one-and-a-half-brick (327.5mm) solid wall

The bare, uninsulated Victorian/Edwardian solid wall — before any lining.

A bare one-and-a-half-brick solid wall — 327.5mm of brickwork (a brick’s length, 215mm, plus its width, 102.5mm, and the 10mm joint between them) — has a U-value of about 1.61 W/m²K with 13mm of dense plaster, calculated at BR 443’s conductivity for brickwork. 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.

Open this build-up in U-Monkey — pre-filled, free

Every layer editable · live U-value · Part L & Future Homes Standard targets · free PDF report

The build-up (outside → inside)

Typical U-values for this construction

SpecificationU-value (W/m²K)Notes
Bare 1½-brick wall (uninsulated)≈ 1.61The starting point — needs insulating
+ 80mm PIR internal insulation (IWI)≈ 0.24The usual retrofit; see the solid-brick + internal insulation page
+ 110mm grey EPS external insulation (EWI)≈ 0.24Keeps internal space; the brick behind it counts as protected (λ 0.56). See the solid-brick + external insulation page

Figures computed with the BS EN ISO 6946 combined method and BR 443 conventions — bridging, mortar joints in blockwork (and in solid brickwork where BR 443 §4.2 requires them) and the air-gap correction included — exactly as the pre-filled calculator works them out, with any pass or fail judged on the unrounded U-value. Indicative for the generic build-up shown: your products, thicknesses and (for floors) footprint will move the number, and 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 £25 +VAT a junction):

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 (327.5mm) solid wall?

A bare one-and-a-half-brick solid wall — 327.5mm of brickwork (a brick’s length, 215mm, plus its width, 102.5mm, and the 10mm joint between them) — has a U-value of about 1.61 W/m²K with 13mm of dense plaster, calculated at BR 443’s conductivity for brickwork. 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 327.5mm (one-and-a-half-brick) solid wall?

Bare, about 1.61 W/m²K with 13mm of dense plaster — 327.5mm is a brick’s length and width plus the joint between them. 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), the condensation-risk screening check and the thermal-mass figures (decrement factor, time lag, κ) 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, mortar joints in blockwork (and in solid brickwork where BR 443 §4.2 requires them) and air-gap corrections, BS EN ISO 13370 for ground floors, suspended floors and basements, and ISO 13788 for the condensation screening check.

Other common build-ups

Walls

Roofs

Floors

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.

Your build-up won't be exactly this one.

It never is. Open this one pre-filled, then swap the insulation, change the thicknesses and watch the U-value move — free, in your browser, with a Building Control-ready PDF at the end.

Open this build-up pre-filled or call 01202 623236