How is a PSI Value Calculated Basic Walk Through - ATSPACE

How do you calculate a PSI value for a thermal bridge junction using CAD and TRISCO? In this in-depth tutorial, we walk through a full PSI value calculation for an E6 intermediate floor junction on a timber frame build. You’ll see the process step-by-step, from converting the client’s PDF detail into CAD, setting up layers and materials, importing into TRISCO, assigning boundary conditions, running the thermal model, and finally calculating the Ψ (psi) value and temperature factor (fRsi) for condensation risk. If you work with SAP, thermal bridging, Psi-value calculations, or detailed junction modelling, this video shows exactly how we build a compliant, auditable calculation that can be used in SAP/PHPP and building regulation submissions. What We Cover - What an E6 intermediate floor junction is in a timber frame build-up - How to convert PDF details to DWG/DXF and clean them in LibreCAD - Creating and organising CAD layers for each material (plasterboard, insulation, timber, chipboard, air cavities, etc.) - Deciding how much of the flanking elements to include (1m or 3 × wall thickness rule) - Scaling drawings correctly from PDF to CAD using known dimensions - Setting up polylines by material and preparing the model for TRISCO - Importing DXF into TRISCO, assigning colours and material properties - Setting and checking boundary conditions (internal, external, horizontal, upward, downward heat flow) - Using the grid, blocks and colours in TRISCO to represent the junction accurately - Running the thermal simulation and extracting Q (heat loss) and minimum internal surface temperature - Converting Q to L2D and deriving the Psi-value (Ψ) in Excel - Calculating the temperature factor (fRsi) to assess condensation / mould risk - Creating a professional Psi-value certificate with drawings and outputs Why Accurate Psi-Value Calculations Matter Getting PSI values right is critical because it helps you: ✓ Improve the accuracy of SAP / SBEM / PHPP energy assessments ✓ Reduce assumed thermal bridging and lower overall fabric heat loss (Y-value) ✓ Demonstrate compliance with building regulations and Appendix K / BR 497 guidance ✓ Prove that junctions are well-designed, reducing cold bridges and condensation risk ✓ Produce professional, repeatable certification that clients, assessors and building control can trust