U-value of an insulated composite panel wall

An insulated composite wall panel with a 100mm PIR core — Kingspan’s QuadCore AWP, λ 0.018 — has a declared U-value of 0.19 W/m²K, well inside the 0.26 Approved Document L Volume 2 sets for a wall; 74mm (0.25) is the thinnest that meets it, and 120mm (0.15) beats the 0.18 the NCM notional building takes for a side-lit building. For a composite panel the maker’s declared value is the one to use: BR 443 says “numerical analysis is needed to take account of joints between panels”, and a layer-by-layer sum of steel, core and steel reads low — 0.17 for this panel, and 0.37 for the 45mm one, declared at 0.46. U-Monkey takes a composite panel at the declared U-value you enter.

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The build-up (outside → inside)

Kingspan QuadCore AWP wall panel: steel outer face, 100mm QuadCore PIR core (λ 0.018), steel inner face, side joints with a factory-applied seal
Entered as one layer at its declared U-value, 0.19 W/m²K (QuadCore AWP data sheet, sixth issue, 3 July 2023; the April 2026 LEC sheet has the same table): R = 1/0.19 − (0.13 + 0.04) = 5.09 m²K/W

The pre-filled link opens in the England · non-domestic regime with the panel as one layer, “Kingspan QuadCore AWP wall panel (100mm core)”, at its declared U-value: U-Monkey takes the panel’s resistance from the U you give it, R = 1/U − (Rsi + Rse), here 1/0.19 − 0.17 = 5.09 m²K/W. Pick another core thickness in its row and U-Monkey fills in Kingspan’s declared U for it; Tata Steel’s Trisomet and Joris Ide’s panels are in the library too, and for any other maker’s panel add the generic one and type its declared U. Declared values are rounded to two places, and the result is no more precise than that.

Typical U-values for this construction

Specification	U-value (W/m²K)	Notes
QuadCore AWP, 70mm core	0.27	Fails 0.26
QuadCore AWP, 74mm core	0.25	The thinnest that meets 0.26
QuadCore AWP, 80mm core	0.23
QuadCore AWP, 100mm core	0.19	As pre-filled
QuadCore AWP, 120mm core	0.15	Beats the side-lit notional 0.18
QuadCore AWP, 150mm core	0.12
Tata Steel Trisomet, 100mm core	0.20	Datasheet (2025): BS EN 14509, computer modelled to BS EN ISO 10211
Joris Ide JI SF Wall 1000, 100mm PIR	0.21	Stated basis “EN 14509:2013”
Stone wool core: Joris Ide JI Vulcasteel Wall, 175mm	0.25	A2-s1,d0 in all but two of its coatings; the thinnest of its sizes to meet 0.26 (240mm: 0.18)
Layer by layer: steel, 100mm core at λ 0.018, steel	≈ 0.17	What BR 443 says not to do — no joints, no fixings (0.175; air gaps level 0, as a foamed core has none)
Layer by layer at 45mm	≈ 0.37	Declared 0.46: the thinner the panel, the more the joints matter

The panel rows are the makers’ declared U-values, which the pre-filled calculator turns into the panel’s resistance (R = 1/U − (Rsi + Rse)) and gives back unchanged; the layer-by-layer rows are the BS EN ISO 6946 combined method with BR 443 conventions at air-gap level 0 (a foamed core has no gaps), shown for comparison only. Declared values are rounded to two places. Joris Ide and Tata Steel figures are from their UK product pages and data sheets, read 13 October 2026.

What changes the number

A composite panel is the one common envelope U-Monkey does not calculate from its layers, because BR 443 (2019) says it cannot be done that way: its wall table says numerical analysis is needed “to take account of joints between panels, if it is thinner at joints or if metal fully or partly penetrates insulation, and to take account of profiled sheets”, and §4.8.3 rules out the ISO 6946 fixings correction “when both ends of the metallic fixing are in direct contact with metal sheets, including composite panels bounded by metal sheets”. Panel makers declare U-values to BS EN 14509, the panel standard, whose Annex A.10 adds the longitudinal joint by a two-dimensional calculation or a tabulated joint factor, and many model them to BS EN ISO 10211; the metal cladding makers’ own guidance had the quoted value including “the thermal bridge at side laps and any through fixings” (MCRMA/EPIC Technical Paper 17, 2007, since withdrawn). How much the joint costs depends on its design: a 2020 finite-element study at RWTH Aachen put a standard joint at about 11–17% of the U-value of 60–140mm panels, and found a leaky joint could add about 0.20 W/m²K through air leakage — which is why side joints are sealed on the liner side. So compare panels on their declared values: at 100mm, QuadCore AWP (λ 0.018) declares 0.19, Tata Steel’s Trisomet 0.20 and Joris Ide’s SF Wall 0.21. A stone wool core (λ about 0.040–0.045), chosen for its reaction to fire, needs nearly twice the depth: Joris Ide’s Vulcasteel wall panel, A2-s1,d0 in all but two of its coatings, reaches 0.25 at 175mm. Where the fire rules for a building restrict combustible materials in its external walls, the core’s class decides which panel can be used: check it against the rules that apply. Approved Document L Volume 2 sets 0.26 for a wall in its 2021 and 2026 editions; for a new building the test is the whole-building calculation — the BER and BPER against the TER and TPER — where the NCM notional building has 0.18 walls if side-lit and 0.26 if top-lit.

Condensation in composite panels

U-Monkey’s free BS EN ISO 13788 check finds no interstitial condensation in the panel: with steel on both faces nothing diffuses in, and panel makers’ declarations of performance give the water vapour permeability as “Impermeable”. A lining added inside a 100mm panel — 50mm of mineral wool and plasterboard — also stays clear, because the panel keeps its inner face warm.

What a one-dimensional check cannot see is the joints. Vapour and air get through them if anywhere — “condensation near the joint is by far more probable than at the centre of the panel”, a 2020 study at ZAG Ljubljana found — so the side-joint seal belongs on the liner (warm) side, and the outer one is “for weather tightness only” (SteelConstruction.info). For a pool, a kitchen or a cold store, take the maker’s advice on joint sealing for the humidity.

Check this build-up for condensation — free

Opens pre-filled. The condensation verdict sits just under the U-value — tap it for the full month-by-month check, the surface-mould (f_Rsi) check included. If it isn’t a pass, How to fix it tests the usual remedies on your build-up — a vapour control layer on the warm side, a more vapour-open layer on the cold side, more insulation to warm the inside surface — and applies the one you pick in a tap, with Undo.

Need it in writing for Building Control? The full condensation risk analysis report is £25 +VAT (£30 inc VAT), or included on Monkey Pro Unlimited — see an example report (PDF), or read what building control expects the analysis to show.

It is a screening to BS EN ISO 13788 (the Glaser method), honestly labelled as one: it does not model air leakage, rain or moisture stored in materials, so for high-risk or heritage constructions a full hygrothermal simulation (BS EN 15026) is the right next step. Figures above use the app’s defaults — Manchester (Ringway) climate, humidity class 3 (dwellings with high or unknown occupancy), a 1-in-10 design year and, on a roof, the surface taken 2 K below the air for night-sky cooling — so pick your nearest weather station for your own build-up: the result can change from one station to another.

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 building'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 an insulated composite panel wall?

Can I calculate a composite panel’s U-value from its core thickness and λ?

Not for compliance. BR 443 needs a numerical analysis of the joints and any fixings, which is what the maker’s declared value (BS EN 14509) contains, and the layer-by-layer figure differs from it: 0.17 for a 100mm QuadCore AWP core against the declared 0.19, and 0.37 against 0.46 at 45mm. Take the declared U for your panel and core thickness from its data sheet. In U-Monkey, pick the maker’s panel from the materials — Kingspan’s QuadCore, Tata Steel’s Trisomet and Joris Ide’s panels are there — and its core thickness, and the declared U fills itself in; for any other panel, add “Insulated composite panel (the maker’s declared U-value)” and type its U into the row. Any lining you add inside is then calculated with it.

Is this calculator free?

Yes — building the element, reading the U-value, the compliance targets (Approved Document L Volume 2 for buildings other than dwellings, and the Welsh and Scottish equivalents), 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 — U-Monkey takes a factory-made composite panel at the maker’s declared U-value, as BR 443 (2019) §4.9 requires a numerical analysis of its joints and fixings (BS EN 14509); everything else uses the combined method of BS EN ISO 6946:2017 with BR 443 conventions, and BS EN ISO 13788 for the condensation 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? For a building other than a dwelling, U-values feed the SBEM calculation that checks the building’s emission and primary energy rates against their targets (BER and BPER against TER and TPER) — and the non-domestic U-value page has the Volume 2 limits. Background reading: what U-values actually are, and why two calculators can give different answers for the same wall.