STA timber thermal bridging guide: psi value insights for UK designers
Reviewed by Tom Sullivan

First reported on The Construction Index
30 Second Briefing
The Structural Timber Association, working with Timber Development UK, Swedish Wood and Knauf Insulation, has launched the Structural Timber Thermal Details platform, a free online library of psi values for timber frame junctions. Developed with Studio Partington Architects and Briary Energy, the resource provides pre-calculated linear thermal transmittance data for common details, supporting more accurate SAP and SBEM assessments. For designers and energy modellers, this should reduce bespoke thermal-bridge calculations and help optimise wall, floor and roof junction specifications in structural timber buildings.
Technical Brief
- Psi-value library targets common cold-bridge junctions in platform-frame and cross-laminated timber assemblies.
- Details explicitly combine structural timber members, sheathing, insulation and linings to reflect buildable junctions.
- Platform is intended to standardise psi assumptions across UK timber designers, assessors and insulation suppliers.
- Consistent psi data should reduce over-conservative Y-values, supporting leaner U-value and insulation specifications.
Our Take
The Structural Timber Association and Timber Development UK both feature repeatedly in our UK coverage, and their parallel leadership changes in 2026 suggest a coordinated push to professionalise guidance and standards around structural timber rather than leaving it to individual designers or suppliers.
Because this is tagged as both Product and Sustainability within our software category, the Structural Timber Thermal Details platform is likely to be picked up by UK housebuilders already engaged with STA’s Westminster advocacy work, giving them a ready-made tool to evidence thermal performance in planning and funding discussions.
In our database, relatively few of the 38 Software stories are tied so closely to a specific material sector, so this STA–TDUK–Swedish Wood collaboration signals that timber is becoming one of the better-served construction materials in terms of digital design and compliance tools in the United Kingdom.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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