Lintel Psi Value Calculator (E1 / E2)

E1 / E2 SAP / Approved Document L reference junction

Schematic cross-section of the lintel (E1 / E2) showing the structure, insulation line and the heat-bridge path — Schematic of the lintel (E1 / E2) — not to scale. Model your actual build-up in ΨMonkey.

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What the lintel is

The lintel spans the head of a window or door opening to carry the wall above it. Steel lintels (E1) and other lintel types (E2) are treated separately in SAP.

Why it matters

A steel lintel is a highly conductive element that can connect the inner and outer leaves directly across the cavity — a classic strong thermal bridge and a frequent condensation point at the head of the opening.

How to model it

Model the lintel profile, any insulation within or behind it, the cavity and the frame at the head. The lintel geometry and its insulation are what drive the Ψ-value.

An insulated or thermally broken lintel performs far better than a bare steel one; the SAP default for steel lintels is high, so calculating is often worthwhile.

Related build-ups: the U-values either side of this junction

The Ψ-value at the lintel depends on the walls, floors and roof around it — so the first step is knowing the U-values of those elements. Typical figures for the build-ups that pair with this junction:

Model your exact build-up and read its U-value with the free U-Monkey calculator (PDFs included free), then come back here and solve the junction in ΨMonkey.

Free to model — no subscription

ΨMonkey isn't a monthly licence or a per-seat subscription. Build the lintel on the grid, solve it, and read the Ψ-value and f_Rsi on screen for nothing. You only pay £25 +VAT (£30 inc VAT), once, when you need the Building Control-ready PDF for that junction — so calculating a single detail never means signing up to anything. Calculated psi values are often the cheapest route to a SAP 10 pass, so the maths can pay for itself.

Frequently asked questions

What is the lintel (E1 / E2)?

The lintel spans the head of a window or door opening to carry the wall above it. Steel lintels (E1) and other lintel types (E2) are treated separately in SAP. A steel lintel is a highly conductive element that can connect the inner and outer leaves directly across the cavity — a classic strong thermal bridge and a frequent condensation point at the head of the opening.

How do I calculate the lintel psi value?

Model the lintel profile, any insulation within or behind it, the cavity and the frame at the head. The lintel geometry and its insulation are what drive the Ψ-value. ΨMonkey solves it to BS EN ISO 10211 and returns the Ψ-value (W/m·K) and the f_Rsi temperature factor on screen, free.

Is it free, and is there a subscription?

No subscription and no licence — modelling the junction and reading off the Ψ-value is free in your browser. You only pay £25 +VAT (£30 inc VAT) when you export the Building Control-ready PDF for that junction.

Can I use the result in a SAP or HEM assessment?

Yes — a calculated Ψ-value to ISO 10211 can replace the SAP default for this junction, and An insulated or thermally broken lintel performs far better than a bare steel one; the SAP default for steel lintels is high, so calculating is often worthwhile.

Other junctions

ΨMonkey models any junction. Jump to another common one:

Lintel Psi Value Calculator