Thermal bridging and energy performance · Lesson 4 of 4

Thermal bridging and energy performance: defects, verification and case study

Where flashing meets the thermal layer, four design defects with their catalogue evidence, a worked case study of metal against membrane flashing at a thermally broken shelf angle, and the record a design team keeps.

You will be able to: Diagnose the common ways sheet-metal flashing defeats the thermal layer, explain the corrective options that belong to the designer of record, and list the evidence a design team keeps.

12 min · 11 slides · 8 questions

All lessons in this module

Slide 1 of 11

Where sheet metal meets the thermal layer

One question for every flashing detail: does any leg cross the insulation or a thermal break?

Five places to ask it: the parapet and coping, a shelf angle, window head flashing, window sill flashing, and floor-line flashing that bypasses exterior insulation.

BC Hydro's catalogue pairs wood-frame rim joist details 8.2.1 and 8.2.2, with and without metal flashing bypassing exterior insulation.

Sources

Building Envelope Thermal Bridging Guide, version 1.3 (2019) - BC Hydro Power Smart (prepared by Morrison Hershfield; BC Housing among the co-sponsors)
Building Envelope Thermal Bridging Guide v1.6, Appendix B: Catalogue Thermal Data Sheets - BC Hydro Power Smart

Glossary

Flashing at a thermally broken shelf angle: BC Hydro's detail 5.2.29 models a thermally broken steel shelf angle with metal flashing and with self-adhered membrane flashing, giving psi 0.41 and 0.234 W/(m·K) at R-15 exterior insulation.
Glazing transition: BC Hydro's name for the interface where wall assemblies meet glazing; its categories run from Efficient (0.2 W/(m·K)) to Poor (0.5), depending on insulation alignment and whether flashing bypasses the glazing thermal break.
Coping (as BC Hydro models it): In BC Hydro's parapet data sheets 5.5.10 and 5.5.11, cap flashing is folded into the exterior heat transfer coefficient rather than modelled as a separate conductor.