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Tier 5 · Architectural Design and Building Science

Thermal bridging and energy performance

Why heat bypasses insulation through metal, the three kinds of transmittance, how the BC Hydro method and ASHRAE 90.1-2022 handle thermal bridges, and where sheet-metal flashing meets the thermal layer.

4 lessons · about 44 min · 12 diagrams · 4 videos

Version 1.0.0

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Lessons

0 of 4 complete

  1. Lesson 1 · 10 min · 10 slides · 7 questions

    Thermal bridging and energy performance: principles and terminology

    Why heat takes the easy path through metal, the three kinds of transmittance (Uo, psi and chi), how psi is found, what AFS tools leave out, and where the designer of record's responsibility begins.

    You will be able to: Define a thermal bridge, tell clear-field, linear and point transmittance apart with their symbols and units, and state who owns the thermal numbers on a project.

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  2. Lesson 2 · 11 min · 12 slides · 8 questions

    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.

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  3. Lesson 3 · 11 min · 11 slides · 8 questions

    Thermal bridging and energy performance: methods and worked application

    The equation for effective U, the seven steps and the takeoff rules, two worked examples with every catalogue input sourced, how the result goes into an energy model, and the record a design team keeps.

    You will be able to: Apply the effective U-value equation and the seven-step method to a parapet and a shelf angle, taking lengths along the plane of heat transfer and recording every input with its units and source.

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  4. Lesson 4 · 12 min · 11 slides · 8 questions

    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.

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Practical task

Build a thermal-bridging review packet for one wall and parapet of your own design (or a project you have worked on): list its linear details, source a psi value for each, work the effective U-value, and check where every flashing leg ends.

Hand in

  • A detail schedule: each linear and point detail on the wall and roof edge, its catalogue detail number and version (or range category), the insulation level, and the source of its psi or chi, each named
  • A takeoff sheet with units: lengths taken along the plane of heat transfer, the wall area, and who or what each length was measured from
  • A worked effective U-value, U_T = (sum of psi x L + sum of chi) / A + Uo, with every input labelled as from the catalogue, from the drawings or assumed
  • A marked-up section of the parapet and one shelf angle or window sill showing where each flashing leg crosses, or stops short of, the insulation and any thermal break
  • A short note to the designer of record listing the questions you could not answer and the corrective options you would put to them

Rubric

CriterionMeets the standard when
SourcesEvery psi, chi and Uo names its document, detail number, version and insulation level; a range category is labelled as an estimate, and nothing is quoted without its source.
TakeoffLengths are along the plane of heat transfer (a parapet by its run along the wall, a balcony where it meets the wall), with units and the drawing each came from.
CalculationThe U_T equation is written out, units are consistent (W/(m·K), m, m² and W/(m²·K), or the Btu set), and the result is checked against the clear-field Uo.
Flashing checkThe section shows whether each metal leg crosses the insulation or a thermal break, and the packet says which catalogue category or detail that corresponds to.
LimitsThe packet states that the catalogue is Canadian design data for specific modelled assemblies and not a code requirement, and that compliance belongs to the designer of record.
Corrective optionsEach defect is answered with options for the designer of record, naming any option the catalogue does not cover as needing its own evaluation.

Module quiz

10 questions drawn from a bank of 31; a new set each attempt. Pass mark 80%.

1. What does ASHRAE 90.1-2022 Section 5.5.5.3 ask of the support of a shelf angle, as the ASHRAE Journal article describes it?
2. Which transmittance is the extra heat flow per length of a detail such as a parapet or shelf angle?
3. In the trade-off path, which column of Table A10.1 supplies the psi or chi of a bridge that does not comply?
4. When does BC Hydro rate a window transition Efficient?
5. In detail 5.2.29, which flashing gives the lower psi on the thermally broken shelf angle?
6. Which of these does this lesson list as evidence a design team keeps?
7. According to BC Hydro, how is a linear transmittance (psi) found?
8. In BC Hydro's parapet categories, which parapet is rated Efficient?
9. How does BC Hydro rate an un-insulated parapet with major conductive bypasses, such as an exposed parapet and roof deck?
10. In the worked parapet example, how does a Poor parapet's heat flow compare with an Efficient one?