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Thermal bridging and energy performance · Lesson 2 of 4

Thermal bridging and energy performance: materials, standards and design constraints

How conductive the metals are in the BC Hydro models, the guide's performance categories for parapets, slabs and glazing, why a catalogue value belongs to one assembly, and the structure of ASHRAE 90.1-2022 Section 5.5.5.

You will be able to: Read the conductivity inputs and performance categories of the BC Hydro guide with their limits, and describe how ASHRAE Standard 90.1-2022 organizes thermal bridging and the three ways to comply.

11 min · 12 slides · 8 questions

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Slide 1 of 12

How conductive is the metal?

Aluminum flashing (14 gauge): 160 W/(m·K).

Sheet steel studs and flashing (18 gauge): 62 W/(m·K).

Structural steel shelf angle and bolts: 50 W/(m·K).

Stainless steel fasteners: 17 W/(m·K).

A 1 in thermal-break pad: 0.2 W/(m·K).

Wood blocking in the parapet details: 0.09 W/(m·K).

These are model inputs, not material specifications.

Sources

Glossary

Performance category
BC Hydro's rating of a detail from Poor to Efficient by its linear transmittance, with separate ranges for slabs, glazing transitions, parapets and other interface details.
Thermal break
BC Hydro's glossary: a non-conductive material that interrupts a conductive heat flow path. In detail 5.2.29 its catalogue models a 1 in thermal-break pad at 0.2 W/(m·K).
Stand-off (spaced) shelf angle
A shelf angle held off the slab edge on discrete supports so that continuous insulation can pass behind it; BC Hydro's slab categories list stand-off shelf angles as an Improved example.
Unmitigated and Default values
In ASHRAE 90.1-2022 trade-off calculations, a bridge that does not comply takes its psi or chi from the Unmitigated column of Table A10.1 (or another recognized source), and, in a project that mixes compliant and non-compliant bridges, a compliant bridge takes the Default column.