U-value of a solid brick wall (9-inch, uninsulated)

A 215mm (9-inch) solid brick wall with 13mm of dense plaster has a calculated U-value of about 2.1 W/m²K, using BR 443’s conductivity for brickwork exposed to the weather (λ 0.77). That is the figure a U-value calculation, and so a Part L appraisal of the wall, starts from. Real walls usually do better: BRE measured 85 solid brick walls in English homes in 2014 and found an average of 1.57, and RdSAP 10 now assumes 1.7 for a wall 200–280mm thick. Whichever you use, it is far above the 0.70 at which Approved Document L counts a wall as one to upgrade, and about twelve times the 0.18 of a new-build wall.

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

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The build-up (outside → inside)

215mm solid brickwork (9-inch, the bricks laid across the wall)
13mm dense gypsum plaster

The pre-filled link opens as an existing element, judged against Approved Document L’s 0.70 threshold (2021 edition, Table 4.3). Brick at BR 443’s λ 0.77 throughout; there is no cavity, so no air-gap correction or wall ties.

Typical U-values for this construction

Specification	U-value (W/m²K)	Notes
215mm brick, unplastered	≈ 2.23	A garage or outbuilding wall
215mm brick + 20mm lime plaster	≈ 2.09	Lime instead of gypsum makes almost no difference
215mm brick + 13mm dense plaster	≈ 2.10	The calculated figure, as pre-filled
RdSAP 10 default, solid brick 200–280mm	1.7	An assumed value for EPCs, down from 2.1 after BRE’s field measurements (CONSP:16, 2016)
Measured: 85 solid brick walls (BRE, 2014)	1.57 (mean)	In-situ heat-flux measurements; the same walls calculated at 1.90 on average
One-and-a-half brick (327.5mm) + plaster	≈ 1.61	See the 1½-brick wall page
Half brick (102.5mm) + plaster	≈ 3.04	Single-skin extensions and outbuildings

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

Nothing about a bare wall moves the number much except its thickness: 215 to 327.5mm takes it from 2.1 to 1.6. The calculation uses BR 443’s λ 0.77, the cautious value for brick that gets wet; drier brick, lime mortar and the air in the joints are why measured walls come out lower. Neither figure changes the answer, which is insulation — internal or external — and on a solid wall that is a moisture decision as much as a thermal one. U-Monkey opens this wall as an existing element, judged against the 0.70 threshold; switch the work type to “upgrade” and add a lining to see what reaches the 0.30 Approved Document L asks of an insulated wall.

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 solid brick wall (9-inch, uninsulated)?

Why is a solid wall 2.1 in one place and 1.7 in another?

2.1 is the calculation: BS EN ISO 6946 with BR 443’s conductivity for brick. 1.7 is RdSAP 10’s default for a solid brick wall 200–280mm thick (Table 13 of the June 2026 specification, version 4.0), which BRE proposed in 2016 after measuring 85 solid brick walls in English homes and finding an average of 1.57 W/m²K, against 1.90 calculated for the same walls and the 2.1 RdSAP then assumed. An EPC uses the default; a U-value calculation for Building Control uses the conductivities, so it gives the higher figure. Both say the wall loses heat roughly ten times faster than a new one.

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.