Cold Bridging Explained

Cold Bridging Explained: A Complete Guide to Thermal Bridges, Surface Temperatures and Robust Junction Design

Published by Houseplansdirect, Version 3.0 of this technical guide provides structural diagrams, system breakdowns, and regulatory guidance for managing local heat-flow paths and surface condensation risks across domestic building envelopes in England.

Key Topics Covered

• Core Principles & Classification: Defines thermal bridging mechanisms and differentiates between repeating bridges (e.g., timber studs or mortar joints calculated in U-values), linear bridges ($\psi$-values along floor or opening junctions), point bridges ($\chi$-values from structural fixings), and geometric bridges.

• Heat Flow, Condensation & Mould Risk: Explores two- and three-dimensional heat transfer, internal surface temperature factors ($f_{Rsi}$), dew-point dynamics, and how thermal performance interacts with ventilation and relative humidity to prevent surface condensation and mould.

• Anatomy of Critical Junctions: Visual breakdowns of major building envelope intersections, including wall-to-floor edges, eaves, verges, lintels, window/door frames, intermediate floors, and cantilevered projections like balconies.

• Design, Calculation & Mitigation: Workflow strategies for tracing continuous insulation layers, setting up a junction schedule, and applying two-dimensional numerical modelling (BS EN ISO 10211 / ISO 14683). Details structural break components, thermally improved cavity closers, and insulated lintels.

• Regulatory Compliance & Defect Prevention: Aligned with Building Regulations Approved Document L (Volume 1), SAP energy assessment methods, Parts C (Moisture) and F (Ventilation), and Regulation 7. Features an illustrated troubleshooting matrix for common site defects (e.g., insulation gaps, misaligned window frames, steel projections), a staged inspection checklist with hold points, an thermal physics glossary, and FAQs.

For a key junction around wall openings, see our Cavity Closers Explained guide. The government’s Approved Document L provides technical guidance on limiting thermal bridging.