Ground floor perimeter junctions (E1-E5), intermediate floor junctions (E6-E7). Critical for SAP y-values and heat loss calculations.
Eaves (E16-E17), verge, gable, ridge and flat roof junctions. Room-in-roof details including dormer windows.
Head, jamb and sill details (E10-E15). Window installation positions optimised to minimise thermal bridging.
External and internal wall corners (E8-E9). Corner details can significantly impact overall thermal performance.
Party wall to external wall, floor and roof junctions (E19-E24). Essential for terraced and semi-detached dwellings.
Balconies, canopies, structural penetrations, steel frames and other non-standard junctions requiring bespoke analysis.
A Psi value (ψ-value, linear thermal transmittance) measures heat loss at junctions where building elements meet—such as wall-floor junctions, window reveals, corners and eaves. It's measured in W/mK and represents the additional heat loss per metre length of the junction beyond what the U-values of the elements alone would predict.
Thermal bridges at junctions can account for 20-30% of total heat loss in well-insulated buildings. Accurate Psi values are essential for SAP calculations, meeting Part L requirements, and avoiding condensation and mould risks. Using calculated Psi values instead of defaults can significantly improve your SAP rating.
Building Regulations allow use of default (Accredited Construction Details) Psi values, but these are often conservative. Calculated Psi values based on your actual details typically show better performance, improving SAP ratings. For challenging projects or marginal compliance, calculated values are essential.
Common junctions include: wall-floor (ground and intermediate), wall-roof (eaves, verge, ridge), wall-wall (corners), window/door perimeters (head, jamb, sill), party wall junctions, balconies and other penetrations. We calculate all relevant junctions for your project.
We use 2D thermal modelling software compliant with BR 497 and BS EN ISO 10211. The junction geometry and materials are modelled, and heat flow is simulated to determine the linear thermal transmittance. Results are validated against industry standards and presented in a format suitable for SAP.