Building Envelope Thermal Bridging Guide

Placeholder page for the supporting reference Building Envelope Thermal Bridging Guide, part of the Examitect reading list for the ExAC.

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Building Envelope Thermal Bridging Guide at a glance

Here is the at-a-glance summary an Intern Architect can scan before opening the Guide for the first time.

Full titleBuilding Envelope Thermal Bridging Guide, Analysis, Applications, and Insights (Version 1.6)
PublisherBC Housing. Earlier versions were commissioned by BC Hydro Power Smart and prepared by Morrison Hershfield.
Current editionVersion 1.6, 2021
Earlier editionsVersion 1.0 in 2014, with incremental updates that added new assemblies and interface details. Version 1.6 added 26 new details and 95 new scenarios, plus precast concrete, wood-framed, and roofing assemblies.
LanguagesEnglish
Primary audienceArchitects, building envelope consultants, energy modellers, mechanical engineers, and code officials working with the NECB, the BC Energy Step Code, and provincial energy regulations.
ExAC relevanceSupplementary resource on Examitect's ExAC study plan. Section 2 objectives 5.21 and 5.22 cite Sections 1, 2, 3, and 4 of the Guide. Section 3 objectives 8.2 and 8.3 cite Sections 3 and 4 of the Guide.
Where to accessFree PDF, commonly available through BC Housing's research centre. Check the publisher's site for the current version and any addenda.

Why the Thermal Bridging Guide matters for the ExAC

The Thermal Bridging Guide is the place where the vague phrase "continuous insulation" turns into a number. Examitect's ExAC study plan lists it under four objectives across two sections: Section 2 objectives 5.21 and 5.22 (environmental separation and building envelope performance under NBC Part 5), and Section 3 objectives 8.2 and 8.3 (construction principles and systems, and assemblies and details).

The Guide will not be the primary basis of an exam question. The primary references for those four objectives are the NBC 2020 Part 5, CHING, and CHOP. But the vocabulary the Guide defines, including effective R-value, clear field transmittance, linear transmittance (psi-value), point transmittance (chi-value), and interface detail, 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. The Guide is the resource that teaches you to recognize it.

ExAC sections this reference supports

Section 1
Section 2
Section 3
Section 4

What the Building Envelope Thermal Bridging Guide is

The Building Envelope Thermal Bridging Guide is a methodology document and a catalogue. Its stated purpose is to help the construction sector deliver more energy-efficient buildings by addressing the current obstacles to accounting for thermal bridging and showing opportunities to improve envelope thermal performance.

The methodology pages explain how three-dimensional heat transfer analysis is used to derive accurate effective R-values for real assemblies. The catalogue pages report those effective R-values, along with linear and point thermal transmittances, for a wide range of typical Canadian wall, roof, floor, and interface details. The Guide covers wood-framed, steel-stud, concrete, masonry, and precast concrete construction, and it includes details for window-to-wall transitions, intermediate floors, parapets, balconies, roof penetrations, and base-of-wall conditions at foundations.

The Guide is not a code and not a textbook. It is a reference that translates between an architect's detail drawings and the effective thermal performance numbers that the NECB 2020 and the BC Energy Step Code require.

Inside the Building Envelope Thermal Bridging Guide

The Guide is organized into four main sections. Examitect's ExAC study plan points to Sections 1 through 4 for Section 2 envelope categories, and to Sections 3 and 4 for Section 3 assembly categories, so it pays to know what each section contains.

SectionWhat it coversWhere it lands on the ExAC
Section 1, Background and methodology Definitions of thermal bridging, types of thermal bridges (clear field, linear, point), the role of effective R-value, and the three-dimensional heat transfer analysis approach used throughout the catalogue. Section 2 background. Useful for any envelope or NBC Part 5 question.
Section 2, Building envelope assemblies and interfaces Methodology for evaluating individual assemblies and the details where assemblies meet. Frames the difference between clear field performance and the additional losses at interface details. Section 2 envelope performance. Background for questions about heat, air, and moisture coordination under NBC Part 5.
Section 3, Catalogue of details Effective R-values, linear transmittances (psi-values), and point transmittances (chi-values) for typical wall, roof, floor, and interface details, including wood-frame, steel-stud, concrete, masonry, and precast concrete construction. The core testable material for Section 2 envelope performance and Section 3 assemblies. Use as a recognition tool, not a memorization target.
Section 4, Applications and insights Whole-building thermal performance, worked applications, design recommendations, and insights for integrating thermal bridging analysis into energy code compliance and design decisions. Section 3 assemblies and detailing. Background for whole-building performance questions.
Appendices and references Glossary, references, and supporting material. Useful as a study glossary for envelope vocabulary. Reference; use as a glossary.

If you are short on time, read Section 1 in full to learn the vocabulary, skim the catalogue in Section 3 to recognize the typical thermal bridge offenders, and read Section 4 for the whole-building picture. 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.

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, and the value referenced by the NECB.
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 heat, air, vapour, water, and 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 method 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 primary control functions of an envelope assembly under NBC Part 5. Thermal bridging undermines heat control and can drop surface temperatures below the dew point, creating condensation risk.

How the Thermal Bridging Guide compares to other ExAC references

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

ReferenceWhat it's 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 2020Mandatory national energy code for buildings.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 2.5 and 5.4The architect's responsibilities around construction principles, assemblies, and detailing.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.
Designing Exterior Walls According to the Rainscreen PrincipleRainscreen wall design and detailing.Rainscreen detailing creates the cavity where continuous insulation and cladding fasteners live; the Guide quantifies the resulting thermal bridging.
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 to study the Thermal Bridging Guide for the ExAC

  • Anchor the vocabulary first. Read the methodology pages and learn nominal vs. effective R-value, plus the three transmittance types (clear field, linear or psi-value, point or chi-value). These five terms carry the rest of the Guide.
  • Recognize the three control layers. The Guide is built around the heat, air, and moisture functions that NBC Part 5 requires. Be able to name them in a typical wall, roof, and slab assembly and identify where thermal bridging breaks each one.
  • Skim the catalogue once. Do not memorize numbers. Look at the range of assemblies (wood-frame, steel-stud, concrete, masonry, precast) and notice which assemblies and which interface details have the worst effective R-value losses.
  • Study the interface details in depth. Window-to-wall, intermediate floor, parapet, base of wall, and roof penetration are where most envelope heat loss happens. These are the moments the ExAC will test.
  • Connect the Guide to NBC Part 5 and the NECB. The Guide is the technical bridge between the regulatory requirements in NBC Part 5 and the energy-performance numbers in the NECB.
  • Use the Guide alongside CHING Chapter 7 (moisture and thermal control) and CHOP Chapter 5.4 (drawings and specifications). Those are the primary references; the Guide quantifies what they describe.

ExAC sections the Thermal Bridging Guide supports

Examitect's ExAC study plan lists primary and supplementary resources for each category. Here is where the Building Envelope Thermal Bridging Guide shows up on that plan.

ExAC sectionHow the Guide shows up on Examitect's study plan
Section 1
Design and analysis		Not listed. Section 1 envelope content is covered through programming, site analysis, and schematic design references.
Section 2
Codes		Listed as a supplementary resource for objective 5.21 (Understand environmental separation requirements) and objective 5.22 (Understand building envelope performance) under NBC Part 5. Primary references are NBC 2020 Sections 5.1, 5.3 to 5.6, and Part 5 generally.
Section 3
Sustainability and final project		Listed as a supplementary resource for objective 8.2 (Understand construction principles and systems) and objective 8.3 (Evaluate assemblies and details). Primary references are CHING Chapters 3 through 10 and CHOP Chapters 2.5, 5.4, and 6.4. Examitect's study plan points to Sections 3 and 4 of the Guide for these.
Section 4
Construction and practice		Not listed. Section 4 is covered primarily by CHOP, RAIC Documents 6 and 9, and the CCDC contracts.

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, including 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 all 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 a supplementary resource on Examitect's ExAC study plan. 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 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.

Building Envelope Thermal Bridging Guide and ExAC FAQ

The Building Envelope Thermal Bridging Guide is a free publication produced by BC Housing, with earlier versions commissioned by BC Hydro Power Smart and prepared by Morrison Hershfield. 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's ExAC study plan lists the Thermal Bridging Guide as a supplementary resource. It supports Section 2 objectives 5.21 and 5.22 (environmental separation and building envelope performance under NBC Part 5) 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's study plan points to Sections 1 through 4 of the Guide for the Section 2 categories, and to Sections 3 and 4 of the Guide for 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 2.5 and 5.4.

The Guide is published by BC Housing and is typically available at no cost through BC Housing's research centre. 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 ExAC study plan. 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 2.5 and 5.4 set the architect's responsibilities around assemblies and construction documents.

BC Step Code Design Guide

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

Supporting references

The extended reading list of supplementary references that show up across the ExAC reading list.