Supporting Reference

Building Envelope Thermal Bridging Guide for the ExAC

The Building Envelope Thermal Bridging Guide (Version 1.6, 2021), published by BC Hydro Power Smart and prepared by Morrison Hershfield, is the standard Canadian reference for accounting for thermal bridging in opaque envelope assemblies. Examitect treats it as supplementary reading for envelope and environmental separation in Section 2 and for building science, assemblies, and detailing in Section 3.

Try a free ExAC practice question See plans

Building Envelope Thermal Bridging Guide overview

Thermal Bridging Guide at a glance

Full titleBuilding Envelope Thermal Bridging Guide (Version 1.6, 2021)
PublisherBC Hydro Power Smart. Prepared by Morrison Hershfield, with co-sponsors including BC Housing, CMHC, the Canadian Wood Council, and Natural Resources Canada.
Current editionVersion 1.6, 2021
Earlier editionsVersion 1.0 in 2014, with incremental updates. Version 1.6 added 26 new details and 95 new scenarios, including precast concrete, wood-framed, and roofing assemblies.
LanguagesEnglish
Primary audienceArchitects, building envelope consultants, energy modellers, and code officials working with the NECB and provincial energy regulations.
ExAC relevanceSupplementary reference in Examitect's study guidance. Sections 1 to 4 of the Guide support Section 2 objective 5.3.4; Sections 3 and 4 support Section 3 objectives 8.2 and 8.3.
Where to accessFree PDF, available through BC Hydro Power Smart. Check the publisher's site for the current version and any addenda.

Why the Guide matters for the ExAC

The Thermal Bridging Guide is the place where the phrase "continuous insulation" turns into a number. It is both a methodology document and a catalogue: the methodology pages explain how three-dimensional heat transfer analysis derives accurate effective R-values for real assemblies, and the catalogue reports those values for a wide range of typical Canadian wall, roof, floor, and interface details.

Examitect treats it as a supplementary reference across two sections: Section 2 objective 5.3.4, applying prescriptive Code requirements concerning envelope design to a building governed by Part 9 of Division B, and Section 3 objectives 8.2 and 8.3 (construction principles, systems, assemblies, and details). The vocabulary it defines, including effective R-value, clear field transmittance, psi-value, and chi-value, can appear in scenario questions that ask which detail option performs best from a thermal standpoint.

Recognizing which assembly bypasses the insulation layer, and which interface detail mitigates that bypass, is the testable skill.

How to study the Guide for the ExAC

  • Anchor the vocabulary first: nominal vs. effective R-value, plus the three transmittance types (clear field, linear or psi-value, point or chi-value).
  • Recognize the three control layers (heat, air, moisture) and where thermal bridging breaks each one in typical wall, roof, and slab assemblies.
  • Skim the catalogue in Appendices A and B once to see which assemblies and interface details are the worst thermal bridge offenders. Do not memorize numbers.
  • Study interface details in depth: window-to-wall, intermediate floor, parapet, base of wall, and roof penetration. These are where most envelope heat loss happens.
  • Connect the Guide to NBC Part 5 and the NECB 2020: the Guide is the technical bridge between the regulatory requirements and the energy-performance numbers.
  • Use the Guide alongside CHING Chapter 7 (moisture and thermal control) and CHOP Chapters 6.3 and 6.4, which cover design development and construction documents, where envelope decisions get documented.

Inside the Building Envelope Thermal Bridging Guide

The Guide is organized into seven numbered sections plus the appendices that hold the thermal performance catalogue. Examitect's study guidance points to Sections 1 through 4 for the Section 2 envelope category, and Sections 3 and 4 for the Section 3 assembly categories, so it pays to know what each part contains.

SectionWhat it coversWhere it lands on the ExAC
Section 1: Overview What thermal bridging is, why it matters for energy performance, and why current energy codes and standards do not yet effectively address it. Section 2 background. Useful for any envelope question.
Section 2: Glossary Definitions of the Guide's terms, including clear field, linear, and point transmittances and effective R-value. Quick vocabulary reference for both ExAC sections.
Section 3: Methodology for Determining Thermal Performance The three-dimensional heat transfer analysis approach used to derive the catalogue values, and how clear field, linear (psi-value), and point (chi-value) transmittances are calculated and combined. The core methodology material for Section 2 envelope performance and Section 3 assemblies.
Section 4: Summary of the Thermal Performance Catalogue An overview of the assemblies and interface details covered by the catalogue and what the results show about typical Canadian construction. Recognition material for Section 2 envelope performance and Section 3 assemblies and detailing.
Section 5: Example Utilization Worked examples that apply the catalogue values to whole-building thermal performance and design comparisons. Background for whole-building performance questions.
Section 6: Inputting Thermal Values into Energy Models How to carry effective R-values and transmittances into energy modelling software. Reference only for the ExAC.
Section 7: References The standards, studies, and modelling sources the Guide draws on. Reference only for the ExAC.
Appendices A and B: The thermal performance catalogue Appendix A holds the catalogue material data sheets and Appendix B the thermal data sheets: effective R-values, linear transmittances (psi-values), and point transmittances (chi-values) for wood-frame, steel-stud, concrete, masonry, and precast wall, roof, floor, and interface details. The core recognition tool. Skim it to spot typical thermal bridge offenders; do not memorize numbers.

If you are short on time, read Sections 1 to 3 to learn the vocabulary and methodology, read Section 4 for the catalogue summary and the whole-building picture, and skim the catalogue data sheets in Appendices A and B to recognize the typical thermal bridge offenders. The catalogue numbers themselves are reference material.

Key Thermal Bridging Guide terms every ExAC candidate should know

The Guide is precise about its vocabulary. Learn these terms early so scenario questions read clearly under exam pressure. Environmental separation comes from NBC 2020 Part 5 rather than the Guide itself, and Part 5 covers sound transfer as well as heat, air, and moisture; exam questions often pair them with the Guide's vocabulary.

TermWhat it means in the Guide
Thermal bridgeA localized area of the envelope with higher heat flow than the surrounding assembly, caused by materials or geometry that interrupt or bypass the insulation layer.
Effective R-valueThe thermal resistance of a complete assembly accounting for framing, fasteners, and thermal bridges. Always lower than nominal R-value; the Guide's catalogue reports effective values for full assemblies.
Nominal R-valueThe rated resistance of an insulation product on its own, tested under standardized conditions. Does not reflect installed assembly performance.
Clear field transmittanceHeat flow through the typical, repeating area of an assembly away from any interface or anomaly. Expressed in W/m2K.
Linear transmittance (psi-value)The additional heat flow along a continuous detail such as a slab edge, parapet, or window perimeter, beyond the clear field. Expressed in W/mK.
Point transmittance (chi-value)The additional heat flow through a discrete penetration such as a balcony connector or a structural anchor, beyond the clear field. Expressed in W/K.
Environmental separationThe function of an envelope assembly under NBC 2020 Part 5: separating conditioned interior from exterior or ground, controlling the transfer of heat, air, moisture, and sound, controlling condensation, and carrying structural loads.
Continuous insulationInsulation installed in an uninterrupted layer outboard of the structural framing, intended to reduce thermal bridging through studs, joists, or slabs.
Interface detailA junction where assemblies meet (window-to-wall, parapet, intermediate floor, base of wall, roof penetration). Where most thermal bridging occurs.
3D heat transfer analysisNumerical simulation that models heat flow through three-dimensional geometry. The Guide uses 3D analysis to derive its transmittance values.
Whole-building thermal performanceThe combined effect of clear field, linear, and point transmittances across opaque envelope areas, plus fenestration U-values, used for code compliance and design comparisons.
Heat, air, and moisture controlThe three control functions the Guide works with. NBC 2020 Part 5 covers the transfer of heat, air, moisture, and sound, so sound transmission (Section 5.8) and structural loads (Subsection 5.2.2) sit alongside them. Thermal bridging undermines heat control and can drop surface temperatures below the dew point, creating condensation risk.

Tips for Intern Architects reading the Thermal Bridging Guide

The Guide is written for working envelope consultants and energy modellers, not students. If you are early in your internship under the Internship in Architecture Program (IAP), here is how to read it efficiently.

Tip 1, learn the three transmittance types as a sentence. Clear field is the typical area, linear (psi-value) is the continuous detail, point (chi-value) is the discrete penetration. Write those three definitions on a single card. Most scenario questions can be answered once you place the detail in one of the three categories.

Tip 2, separate nominal from effective R-value. R-22 batt insulation in a 2x6 steel-stud wall does not give you an R-22 wall. Effective R-value, after framing and any continuous insulation, is often dramatically lower. The NECB references effective values, not nominal. This distinction is testable.

Tip 3, focus on interface details, not clear field. Most thermal bridging happens at junctions: window-to-wall, parapet, slab edge, balcony, and base of wall at foundation. The Guide added new interface details in Version 1.6 specifically because this is where the largest losses occur. Spend your study time here.

Tip 4, recognize the worst offenders. Cantilevered concrete balcony slabs, steel shelf angles, parapets without insulation continuity, and unmitigated window-frame thermal bridges show up repeatedly in the catalogue as poor performers. If a question shows you one of these, expect the answer to involve breaking or mitigating the thermal bridge.

Tip 5, link thermal bridging to condensation risk. The interior side of a thermal bridge runs colder than the surrounding wall. If it drops below the interior dew point, you get condensation, then mould, then call-backs. Thermal bridging is a heat, air, and moisture issue, not just an energy issue. NBC Part 5 reads the same way.

Tip 6, treat the catalogue as a reference, not a study target. The numbers change between editions and assemblies. The ExAC will not ask you to recall a psi-value from memory. It will ask whether you can identify the detail that needs improvement.

Tip 7, do not over-invest. The Guide is supplementary reading in Examitect's study plan, not a document the exam body names. Spend most of your envelope study time on NBC Part 5, CHING, and CHOP. Use the Thermal Bridging Guide to deepen your vocabulary and pattern recognition. One focused reading is enough.

Common ExAC scenarios where the Thermal Bridging Guide is the answer

These question types come up in Section 2 envelope categories and Section 3 assemblies categories. If you see one, the Thermal Bridging Guide's vocabulary is what the question is testing.

  • A wall section shows R-22 batt insulation between steel studs with no continuous outboard insulation. Which option best improves the effective R-value of the wall without changing its overall thickness significantly?
  • A cantilevered concrete balcony slab extends from the floor plate through the wall to the exterior with no thermal break. What detailing options would the architect propose to mitigate the linear thermal bridge?
  • A parapet detail shows the structural slab continuing past the wall plane to support the roof membrane upturn. From a thermal bridging standpoint, what is the issue, and what detailing approach would the Guide recommend?
  • A window installation is shown with the frame aligned to the structural sheathing, outboard of the continuous insulation. The reviewer flags a potential thermal performance issue. What is the concern, and what design move addresses it?
  • A small commercial project must demonstrate compliance with NBC 2020 Part 5 for environmental separation. Which of the proposed wall assemblies provides the best balance of effective R-value, condensation control, and constructability?
  • An energy modeller reports that the assumed clear field U-value gives the project a passing score, but the energy advisor wants to include linear transmittances at all interfaces. What is the likely impact on the calculated performance, and how should the architect respond?
  • A project in a cold climate shows visible interior surface condensation at corners and slab edges. From an envelope perspective, what is the most likely cause, and what design changes would the Guide recommend?

Each scenario can be answered by placing the detail in the clear field, linear, or point transmittance category, then recognizing which design move improves the effective performance.

How the Thermal Bridging Guide compares to other ExAC references

The Guide sits beside several other envelope and energy references on Examitect's reading list. Use this comparison to decide what to read for which kind of question.

ReferenceWhat it is forHow the Thermal Bridging Guide relates
Building Envelope Thermal Bridging GuideMethodology and catalogue for thermal performance of opaque envelope details.The catalogue of effective R-values and transmittances for typical Canadian assemblies.
NBC 2020, Part 5Environmental separation requirements for heat, air, vapour, water, and structural loads.NBC Part 5 sets the regulatory framework; the Guide provides the numbers that prove an assembly meets it.
NECB 2020National model energy code for buildings. It has no force of law until a province or territory adopts it.The NECB requires effective R-values; the Guide explains how to calculate them.
CHING (Building Construction Illustrated)Building science, assemblies, materials, and detailing in plain illustrated form.CHING explains the assemblies; the Guide quantifies their thermal performance.
CHOP, Chapters 6.3 and 6.4Design development and construction documents: how envelope decisions are developed, documented, and coordinated.CHOP frames the practice; the Guide is the technical reference that supports it.
BC Energy Step Code Design GuideDesign strategies to meet the BC Energy Step Code in Part 3 buildings.The Design Guide names thermal bridging as one of eight key strategies; the Thermal Bridging Guide is the deeper technical reference behind that strategy.
Performance of Thermal Insulation on the Exterior of Basement WallsBelow-grade insulation strategies.Companion supplementary reference for base-of-wall and foundation interface details.

How Examitect reinforces the Thermal Bridging Guide

Reading the Guide once builds the envelope vocabulary an Intern Architect needs. Examitect's question bank draws on that vocabulary for Section 2 envelope and environmental separation items and Section 3 assemblies and detailing items, including scenario questions about effective R-value, interface details, and condensation risk. Each answer explanation points back to the specific concept the question is testing, so you can re-read just the few pages of the Guide that matter rather than the whole document.

You also get full-length mock exams that mirror ExAC pacing and free study notes for every section. Try a few sample questions first, then check pricing when you want the full bank.

FAQ

Building Envelope Thermal Bridging Guide FAQ

The Building Envelope Thermal Bridging Guide is a free publication from BC Hydro Power Smart, prepared by Morrison Hershfield and co-sponsored by organizations including BC Housing, CMHC, and Natural Resources Canada. Version 1.6 was issued in 2021. It provides a methodology for accounting for thermal bridging in opaque building envelope assemblies, along with a catalogue of effective R-values and thermal transmittance values for common Canadian wall, roof, floor, and interface details.

No. Examitect treats the Thermal Bridging Guide as a supplementary reference. It supports Section 2 objective 5.3.4 (prescriptive Code requirements concerning envelope design for a building governed by Part 9 of Division B) and Section 3 objectives 8.2 and 8.3 (building science and systems, and assemblies and detailing). The primary references for these categories are the NBC 2020, CHING, and CHOP.

Section 2 (Codes) for envelope and environmental separation under NBC Part 5, and Section 3 (Sustainability and final project) for building science, systems, assemblies, and detailing. Examitect maps Sections 1 through 4 of the Guide to the Section 2 category, and Sections 3 and 4 of the Guide to the Section 3 categories.

Thermal bridging is heat transfer through materials and components that interrupt or bypass the building's insulation layer. Common examples include steel studs in a wood-stud wall, concrete balcony slabs that extend through the envelope, parapet wall transitions, and structural shelf angles at floor lines. Thermal bridging lowers the assembly's effective R-value, increases heating energy demand, and can drop interior surface temperatures low enough to cause condensation.

Nominal R-value is the rated thermal resistance of an insulation product on its own, tested in a controlled environment. Effective R-value is the thermal resistance of the complete assembly once you account for framing members, fasteners, balcony slabs, and other thermal bridges. Effective R-value is always lower than nominal, and it is the number the NECB 2020 and most provincial energy codes care about.

Clear field transmittance is the heat flow through the typical area of an assembly, away from any interface. Linear transmittance, the psi-value, is the additional heat flow along a continuous detail like a slab edge, parapet, or window perimeter. Point transmittance, the chi-value, is the additional heat flow through a discrete penetration like a balcony connector or a structural anchor. Together they describe the total envelope heat loss.

You do not need to memorize the catalogue. Read the methodology pages to internalize the language (clear field, linear, point, effective R-value, psi-value, chi-value), then skim the catalogue of details to recognize which assemblies and interface details are typical thermal bridge offenders. Pair the reading with NBC Part 5, CHING Chapter 7 on moisture and thermal control, and CHOP Chapters 6.3 and 6.4 on design development and construction documents.

The Guide is published by BC Hydro Power Smart and is typically available as a free PDF through the publisher's website. Check the publisher's site for the current version and any addenda, as the catalogue is updated periodically.

Keep exploring

Other ExAC reference books.

The Thermal Bridging Guide is one of several envelope, energy, and assembly references on Examitect's reading list. Continue with the rest.

NBC 2020

National Building Code of Canada. Part 5 (environmental separation) is the primary reference for the same Section 2 categories the Guide supports.

NECB 2020

National Energy Code of Canada for Buildings. Requires effective R-values, which the Guide explains how to calculate.

CHING

Building Construction Illustrated. Primary reference for the Section 3 assemblies and detailing categories the Guide supports.

CHOP

Canadian Handbook of Practice. Chapters 6.3 and 6.4 set the architect's responsibilities around design development and construction documents.

BC Step Code Design Guide

Names thermal bridging as one of eight key strategies for meeting the BC Energy Step Code.

RSMeans

RSMeans Cost Data. North American construction cost data, used for Section 1 Cost Management questions.

Yardsticks

Hanscomb Yardsticks for Costing. Canadian elemental cost data by building type and region, for Section 1 Cost Management.

Supporting references

The extended reading list of supplementary references that appear across Examitect's ExAC reading list.