Thermal Bridging Calculations
2D and 3D finite element analysis of construction junctions — accurate Psi-values, temperature factors and condensation risk for SAP and Passivhaus compliance.
Thermal bridges at junctions can account for a significant share of a dwelling’s fabric heat loss — and if SAP uses default y-values instead of calculated Psi-values, that penalty is baked into the result. Calculated junctions recover those losses on paper, improve the fabric energy efficiency rating, and flag where surface condensation and mould could form.
What we calculate
Linear Psi-values (Ψ, W/m·K)
2D thermal bridging
Linear thermal transmittance and temperature factor (fRsi) for wall, roof, floor and opening junctions — the standard input for SAP and PHPP.
Read the articlearrow_outwardPoint transmittance (χ, W/K)
3D thermal bridging
Point transmittance for geometrically complex junctions that 2D can’t capture: corners, balcony connectors, structural penetrations, wall ties and helping-hand brackets.
Read the articlearrow_outwardTemperature factor (fRsi)
Surface condensation & mould risk
Temperature factor checked against the BS EN ISO 13788 / BRE IP 1/06 criterion (fRsi ≥ 0.75 for dwellings) to demonstrate condensation and mould resistance.
Read the articlearrow_outwardCalculate only what moves the result
Junction schedule / SAP-impact review
Before you commission anything, we review your details and tell you which junctions actually move the SAP result and are worth calculating. A low-commitment entry point — see pricing.
How it works
Four steps from drawing to report — with the scope and fixed fee confirmed before any work begins.
Send your drawings
Upload or email junction details (PDF/DWG), the build-up / material spec and your U-value targets. A marked-up architectural detail is ideal — we can also work from sketches.
Review & confirmation
We review the information, confirm the junction list, flag anything missing or ambiguous, and approve the scope and fixed fee before any work starts — no surprises.
Simulation
We build the finite element model and run the analysis to BR 497 conventions, extracting Psi-values, χ-values and temperature factors (fRsi).
Report issued
You receive a clear PDF report per junction — geometry, material properties, boundary conditions, heat-flux and isotherm plots, Psi/χ-value, fRsi and the standards applied — ready to drop into the SAP/PHPP file.
Typical turnaround: quick — confirmed with your fee quote, faster on request.
Standards we work to
BR 497
BRE conventions for linear thermal transmittance and temperature factors (SAP-accepted).
BR 443
Conventions for U-value calculations.
BS EN ISO 10211
Thermal bridges: heat flows and surface temperatures — detailed calculations.
BS EN ISO 6946
Building components: thermal resistance and transmittance.
BS EN ISO 13788
Surface temperature and condensation risk (fRsi).
SAP 10 / PHPP
SAP conventions and Passivhaus thermal-bridge methodology.
Pricing
Transparent, fixed fees for standard 2D junctions. The fee is confirmed before work starts — no hourly billing, no surprises.
2D thermal bridges — fixed fee
| Junction type | Fee |
|---|---|
| 1 plane | £125 |
| 2 planes | £150 |
| Ground floor | £150 |
| Suspended ground floor | £175 |
| Party wall to ground floor (P1) | £250 |
| Junction / SAP-impact reviewwaived if 5+ junctions commissioned | £100 |
Prices ex VAT · per junction, per calculation · fixed fee confirmed before work starts · revisions not included (quoted case-by-case) · multi-junction projects priced on request.
3D thermal bridges — request a quote
3D junctions are quoted on request — every geometry is different. Send your detail and we’ll come back with a fixed fee. Junction types we model in 3D:
- check_circle1 plane
- check_circle2 planes
- check_circle3 planes
- check_circleParty wall (P1 junction)
- check_circleBalcony connector
- check_circleHelping-hand / façade bracket
Related reading from the Coef Wall
Need the same junction across many plots or product variants? See parametric simulations.
Frequently asked questions
Do I need calculated Psi-values, or are SAP defaults fine?add
SAP can use default y-values, but they carry a deliberate penalty — the model assumes worse-than-typical junctions. Calculated Psi-values recover that penalty on paper and improve the fabric energy efficiency rating, which often makes the difference on compliance.
What information do you need to start?add
Junction details (PDF or DWG), the construction build-up and material specification, and your U-value targets. A marked-up architectural detail is ideal; we can work from sketches at early design stages.
Can you work from sketches or early-stage details?add
Yes. We regularly work from concept-stage sketches and confirm any assumptions back to you before modelling, so you get useful feedback while the detail can still change.
Do you provide the SAP assessment too?add
No — we provide the Psi-values, temperature factors and reports your SAP assessor or Passivhaus consultant uses. We supply the modelling inputs; we don’t issue the SAP or EPC certificate.
What’s the turnaround?add
Quick — we confirm a turnaround alongside your fixed fee before work starts, and can prioritise on request.
Send us a junction
Share your details and U-value targets, and we’ll confirm the junction list and a fixed fee before any work starts.
Request a quote