Detail readiness
A dimensioned build-up with clear materials, conductivities and interfaces produces a defensible result. Sketches with unresolved cavities or components need clarification before modelling.
Thermal bridging
Psi-value and thermal-bridge calculations
Turn dimensioned junction details into traceable heat-loss values and useful design feedback.
When you need this work
A good U-value does not describe heat flow at junctions. Psi values quantify the additional linear heat loss at details such as wall-to-floor, lintel, jamb, roof and party-wall connections.
We review the proposed junction, identify the calculation convention and establish whether a two-dimensional thermal model is appropriate; some junctions need three-dimensional treatment. Where suitable, we build the two-dimensional model from the construction information supplied. The result can support SAP or SBEM inputs where the relevant methodology permits it. More importantly, the temperature and heat-flow pattern can expose insulation gaps, conductive paths and surface-temperature risks while details can still be improved.
What we check
Design feedback
We explain where heat is bypassing the intended insulation line and can test a defined revision. The objective is a buildable continuous thermal envelope, not simply a lower number.
Repeatable libraries
House-type and construction systems often reuse junction principles. We can organise commissioned details into a controlled schedule so applicability and revisions remain visible.
Common coordination issue
A calculated value belongs to the modelled junction and conventions. Changes to insulation, blockwork, lintels or dimensions may affect its applicability; keep the drawing revision with the value used by the energy assessor.
What you receive
Calculation sheet
Geometry, material inputs, boundary conditions, results and relevant conventions.
Temperature review
Surface-temperature information where included in the agreed scope.
Junction schedule
Values and references formatted for practical use by the assessor and design team.
Getting started
What we need
Junction drawing
Dimensioned detail showing layers, interfaces, fixings and relevant internal and external extents.
Material data
Thermal conductivities, thicknesses and product information for non-standard components.
Intended use
The energy methodology, junction reference, construction type and any project-specific requirements.
Before commissioning
Is a psi value the same as a U-value?
No. A U-value describes heat flow through a plane element. A psi value describes additional heat flow along a junction.
Can you calculate from a typical detail?
Yes, if it is sufficiently dimensioned and the materials and interfaces are defined.
Can one value be used on another project?
Only where the detail, materials, dimensions, conventions and applicability genuinely match. We do not assume transferability without review.
Sources and further reading
Use the edition, jurisdiction and assessment route that apply to the project. Publication of newer guidance does not automatically change an existing project’s requirements.
Send the detail before it becomes a site problem
Provide the drawing, construction build-up and intended calculation use. We will confirm whether the information is ready to model.