E11 / E12 SAP / Approved Document L reference junction
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What the gable junction is
The gable junction is where a gable (end) wall meets the sloping roof, with insulation at ceiling level (E11) or at rafter level (E12).
Why it matters
As with the eaves, keeping insulation continuous where the gable wall meets the roof slope is awkward, and any break gives heat a route out along the line of the gable.
How to model it
Model the gable wall, the roof construction and the insulation line, ensuring the wall and roof insulation connect. Solve for the Ψ-value and f_Rsi.
Calculated gable values usually improve on the SAP default where the insulation is properly carried up to the roof.
Related build-ups: the U-values either side of this junction
The Ψ-value at the gable junction 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 gable junction on the grid, solve it, and read the Ψ-value and fRsi 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 gable junction (E11 / E12)?
The gable junction is where a gable (end) wall meets the sloping roof, with insulation at ceiling level (E11) or at rafter level (E12). As with the eaves, keeping insulation continuous where the gable wall meets the roof slope is awkward, and any break gives heat a route out along the line of the gable.
How do I calculate the gable junction psi value?
Model the gable wall, the roof construction and the insulation line, ensuring the wall and roof insulation connect. Solve for the Ψ-value and f_Rsi. 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 Calculated gable values usually improve on the SAP default where the insulation is properly carried up to the roof.
Other junctions
ΨMonkey models any junction. Jump to another common one:
- Wall-to-Floor Junction E5
- Window Jamb (Reveal) E4
- Window Sill E3
- Lintel E1 / E2
- Eaves Junction E9 / E10
- External Corner E13
- Inverted Corner E14
- Intermediate Floor E6
- Party Wall Junction E15 / P1–P8
- Balcony Junction E8 / E24
- Exposed Floor E20 / E21
Related reading
- Thermal bridging explained — why junctions leak heat and how Ψ-values work
- What is a U-value? — the element-level heat loss this junction links
- SAP 10: what's new — how calculated Ψ-values beat defaults
- SAP calculations — put your Ψ-values to work in the full compliance model
- New Build Compliance Pack — SAP, water, acoustics and air in one