Guidance · 5 min
Why thermal bridging matters in SAP calculations
How junction assumptions affect heat loss and why details should be coordinated early.
Junction heat loss is part of the dwelling
Heat flows not only through the main areas of walls, roofs and floors but also at their junctions and around openings. SAP accounts for this through the applicable thermal-bridging inputs.
Details and calculations must align
A favourable input cannot be separated from the construction detail it represents. The assessment, detail reference and work on site need a coherent evidence trail.
Standard and project-specific approaches
The available approach depends on the construction, detail set and evidence. Do not assume that a value seen on another project transfers automatically.
Review before the model is fixed
Early junction review can prevent a late shortfall and may reveal more proportionate improvements than increasing insulation everywhere.
Building Regulations guidance and assessment methods can change, and transitional provisions may apply. Confirm the correct route for the particular project rather than relying on a general article.