Supporting Reference

Fire Resistance of Gypsum Board Wall Assemblies for the ExAC

Construction Technology Update No. 2, written by M.A. Sultan and G.D. Lougheed and published by the National Research Council of Canada in January 1997, is a four-page bulletin that distils an industry-supported study of 22 gypsum-board wall assemblies into the design rules that drive fire-resistance ratings. Examitect recommends it as a supporting reference for Section 2 (fire safety under the NBC) and Section 3 (Assemblies and Detailing). The ExAC Preparation Guide does not name it.

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Fire Resistance of Gypsum Board Wall Assemblies overview

The NRC bulletin at a glance

Full titleFire Resistance of Gypsum Board Wall Assemblies
AuthorsM.A. Sultan and G.D. Lougheed, senior fire research officers, NRC Institute for Research in Construction
PublisherNational Research Council of Canada (NRC), Institute for Research in Construction
Series and numberConstruction Technology Update No. 2, ISSN 1206-1220
PublishedJanuary 1997
LengthFour pages of body content
LanguagesEnglish (the NRC Publications Archive lists French equivalents for most Construction Technology Updates)
Primary audienceArchitects, engineers, builders, and code authorities working on multi-family residential construction in Canada
ExAC relevanceExamitect-recommended supporting reference for Section 2 fire safety (5.2.2, and 5.3.2 for Part 9 buildings) and Section 3 Assemblies and Detailing (8.3)
Where to accessNRC Publications Archive, free download (DOI 10.4224/40002869). Not a paywalled standard.

Why this bulletin matters for the ExAC

Fire-resistance is an architectural decision long before it is a code-compliance check. Specifying Type-X over regular board, putting channels on the right face, packing rock fibre tightly between studs: these are the choices that make a listed fire-resistance rating (FRR) survive contact with a real construction site.

Examitect points to this four-page bulletin as supporting reading for Section 2 fire safety (5.2.2, interpreting the Code requirements concerning fire safety in a Part 3 building, and 5.3.2, applying the prescriptive safety requirements to a Part 9 building) and for Section 3 Assemblies and Detailing (8.3). It pairs with the companion NRC bulletin on sound transmission, since the research program tested the same wall families for both fire and acoustic performance at the same time.

The NRC tests fed directly into the 1995 National Building Code, growing the listed fire-rated assemblies in Part 9 from 17 to more than 160. The FRR tables in NBC 2020 trace back to this work. You will not be asked to derive an FRR. You will be asked which assembly detail compromises a listed rating and which fix an architect would specify.

How to study this bulletin for the ExAC

  • Start with the Basic Wall Configurations diagram (page 3). Recognize each of the seven framing families by shape before reading the parameter analysis.
  • Learn the direction and magnitude of each variable's effect: board type, density, layer count, thickness, resilient channel placement, and insulation type and installation.
  • Memorize the rock fibre rule: tightly installed rock fibre gave a 60 percent better fire-resistance rating (100 minutes) than the same insulation installed loosely (60 minutes). One fact, multiple exam questions.
  • Internalize the channel placement rule: channels on the fire-exposed single-layer side lower FRR; channels on the unexposed double-layer side raise it.
  • Distinguish load-bearing from non-load-bearing behaviour: in a load-bearing 1x2 wall, the extra layer provides no fire gain; in a non-load-bearing 1x2 it does. Exam questions exploit this distinction.
  • Cross-reference NBC 2020 Subsections 3.1.7, 3.1.8, and 9.10.3. The code's listed assemblies trace directly to this research.

ExAC sections this bulletin supports

  1. Section 2

    Supporting reading for the fire separation and fire-resistance categories under the NBC.

  2. Section 3

    Supplementary for Assemblies and Detailing alongside CHING, CHOP, and the companion NRC sound bulletins.

  3. Section 4

    Indirect. Useful context for construction-review judgment when site conditions threaten a fire separation.

Seven wall families inside the NRC study

The bulletin organizes its 22 tested assemblies into seven Basic Wall Configurations, each with one-layer and two-layer variants and with or without cavity insulation. Recognizing the family is half the work on an exam question that describes a wall and asks what happens to the FRR when one variable changes.

Wall configurationStud and cavityFire-resistance behaviour
Single wood studs 38 by 89 mm studs, 89 mm cavity, 400 mm on centre Baseline. FRR rises with layer count, board density, and tight rock fibre. Channels are not present, so cavity insulation contributes directly to the rating.
Single wood studs with resilient channels 38 by 89 mm studs, 102 mm effective cavity, channels on one face Channel location is the decisive variable. Channels on the unexposed (double-layer) side raise the FRR; on the fire-exposed (single-layer) side they create a hot-gas pathway that can significantly lower it.
Staggered wood studs Two rows of 38 by 89 mm studs on a 38 by 140 mm plate, 140 mm cavity Staggered framing helps STC but does not improve FRR on its own. No particular fire benefit over single-stud framing.
Staggered wood studs with resilient channels Two rows of 38 by 89 mm studs on a 140 mm plate, 153 mm effective cavity Same channel placement rule applies. Channels on the unexposed side improve FRR; on the fire-exposed side they can reduce it.
Double wood studs Two rows of 38 by 89 mm studs on separate plates 25 mm apart, 203 mm cavity Full structural separation. Strong acoustic performance. No particular fire benefit from the double framing itself; assembly FRR is driven by board type and layer count.
Non-load-bearing steel studs (64 mm) 31 by 64 mm steel studs, 600 mm on centre In 2x2 assemblies, stud type is insignificant. Wood-stud 2x2 assemblies provided a slightly better FRR than steel-stud 2x2 assemblies. Glass fibre or wet-sprayed cellulose made no FRR difference in non-load-bearing 1x2 steel-stud walls.
Non-load-bearing steel studs (92 mm) 31 by 92 mm steel studs, 600 mm on centre Same pattern as the 64 mm steel-stud configuration. For 2x2 non-load-bearing walls, stud material matters less than board type, layer count, and insulation installation.

Across all configurations, moving from 1x1 to 2x2 (one layer to two layers on each side) improves the FRR. In load-bearing walls a 1x2 (asymmetrical) assembly behaves like a 1x1, because the fire is assumed to start on the single-layer (weaker) side. In non-load-bearing walls a 1x2 outperforms a 1x1, since that assumption does not apply.

Key terms every ExAC candidate should know

The exam uses this vocabulary without re-defining it. Knowing the terms before you sit the paper means you spend exam time picking the answer, not parsing the question.

TermWhat it means for the ExAC
Fire-resistance rating (FRR) Time in minutes that an assembly resists structural failure, exceeds a specified unexposed-side temperature, or lets flames or hot gases through under a standard fire test (CAN/ULC-S101). The NBC does not list FRRs below 45 minutes, so any assembly under 45 minutes has failed for code purposes.
Type-X gypsum board Generic designation for gypsum board with a specially formulated core that delivers greater fire resistance than regular board. Tested in 12.7 mm and 15.9 mm thicknesses in the NRC project.
Regular gypsum board Standard gypsum board without the Type-X core. The NRC tests used three densities at 12.7 mm thick: 7.27, 7.35 (with glass fibre in the core), and 7.82 kg/m². Density matters: higher density raises the FRR in regular board.
Glass-fibre core Reinforcing fibre embedded in the gypsum core that holds the board together as it cracks under fire exposure. Raised the FRR of a single-layer load-bearing wall by 25 percent compared to a similar board without glass fibre.
1x1, 1x2, 2x2 layups Shorthand for layers of gypsum board on each face. 1x1 is one layer per face; 2x2 is two layers per face; 1x2 (asymmetrical) is one layer on one face and two on the other. The direction of the single-layer face relative to the fire source matters for load-bearing walls.
Resilient channel Thin stepped steel strip about 25 mm wide. One leg fastens to the stud, the other to the gypsum board. Created to improve STC by providing structural discontinuity. Placement is critical for fire: channels on the fire-exposed side can lower FRR by creating a hot-gas pathway through the gap between the stud and the board.
Rock fibre insulation Mineral wool insulation. In the NRC tests, tightly installed in the cavity it gave a 60 percent better fire-resistance rating (100 minutes) than the same insulation installed loosely (60 minutes). The specification must call out tight installation, not just the material.
Glass fibre insulation Fibreglass batt insulation. Present in the cavity of many load-bearing test assemblies, but the bulletin credits only rock fibre with contributing significantly to fire resistance. Had no FRR effect in non-load-bearing 1x2 steel-stud walls. Not a substitute for rock fibre in assemblies where FRR is the constraint.
Load-bearing assembly Wall that carries structural load. A 1x2 load-bearing wall performs like a 1x1, because fire is assumed to start on the single-layer (weaker) side. The extra layer on the unexposed side provides no fire benefit in a load-bearing application.
Non-load-bearing assembly Partition that does not carry structural load. A 1x2 non-load-bearing wall outperforms a 1x1, since the fire-side assumption does not apply. This distinction is a frequent exam trap.
CAN/CSA-A82.27 Canadian standard regulating the use and application of gypsum board cited in the NRC tests. The CSA A82 series has been updated since 1991; check the edition referenced by the NBC you are working with.

Tips for Intern Architects reading this bulletin

This is one of the shorter references on Examitect's reading list. The reading takes under an hour. The challenge is remembering the right details under exam pressure, not absorbing the material in the first place.

Tip 1, start with the figure on page 3. The Basic Wall Configurations diagram is the spine of the bulletin. Every other finding in the text references one of the seven framing families in that figure. Spend a few minutes naming them by shape (single, staggered, double studs; steel; with or without channels) before you read the body text.

Tip 2, lock in the channel-placement rule before anything else. Resilient channels on the fire-exposed (single-layer) face of an asymmetrical wall can lower the FRR. On the unexposed (double-layer) face they raise it. This one detail flips the answer on a surprising number of party-wall questions, and it seems counterintuitive until you understand the hot-gas pathway mechanism.

Tip 3, remember the rock fibre numbers: tight equals 100 minutes, loose equals 60 minutes. Same wall, same insulation, different installation. Specifications and site supervision win FRR points that the test laboratory cannot give back after the fact.

Tip 4, watch the load-bearing assumption. A 1x2 load-bearing wall is no better than a 1x1, because the fire is assumed to start on the weak side. A 1x2 non-load-bearing wall does better than a 1x1. The exam likes scenarios where this distinction decides the answer, so practise both cases until you can call the right one without thinking.

Tip 5, do not confuse acoustic gains with fire gains. Staggered studs and double studs improve STC but not FRR. Asymmetrical 1x2 layups raise STC but do nothing for the load-bearing fire rating. The whole point of the companion NRC bulletins is that these two properties can pull in opposite directions.

Tip 6, read the bulletin next to NBC Subsection 9.10.3. The listed fire-rated assemblies in Part 9 are direct descendants of this research. Cross-checking the two anchors the FRR numbers and assembly families together so you can navigate the code table on exam day.

Tip 7, pair this bulletin with Construction Technology Update No. 1 on sound transmission. The two bulletins come from the same research program. Reading them in sequence shows which design moves help both fire and acoustic performance, which help one while hurting the other, and which are neutral for both. That trade-off logic is exactly what ExAC questions test.

Common ExAC scenarios where this bulletin is the answer

The scenarios below appear in different wording across ExAC sittings. Recognizing the underlying pattern is faster than memorizing facts in isolation. Each scenario maps to a specific NRC finding.

  • A site review finds resilient channels installed on the fire-exposed side of a 1x2 party wall. What does the architect ask the contractor to change, and what is the fire-resistance impact of leaving the channels in their current position?
  • A specification calls for rock fibre batts in a Part 9 party wall but the site supervisor reports the batts are sagging and loose between studs. What is the effect on the FRR and what is the architect's response?
  • A duplex project switches from Type-X to regular gypsum board to reduce cost. Which listed assemblies in NBC Tables 9.10.3.1.-A and 9.10.3.1.-B no longer apply, and what must be done to maintain code compliance?
  • A multi-residential project has a load-bearing 1x2 party wall and the team proposes placing the extra layer on the fire-exposed side to maximize STC. Why does the placement decision matter for fire resistance, and does it change the FRR?
  • A contractor proposes substituting glass fibre batts for rock fibre in a non-load-bearing 1x2 steel-stud wall to save cost. What does the NRC research say about the impact on FRR, and how should the architect respond?
  • A multifamily party wall must achieve both an STC of 50 and an FRR of one hour. Which combination of resilient channels, insulation type and installation, and gypsum-board layers meets both targets without trading one off against the other?
  • A renovation thickens the gypsum board from 12.7 mm to 15.9 mm Type-X in an existing load-bearing 1x2 wall with resilient channels on the fire-exposed side. Does the FRR improve, and why or why not?

Each scenario connects to a specific NRC finding: channel placement, insulation installation quality, board type, layer count and direction, or material substitution. Reading the bulletin once with these patterns in mind locks in the connections quickly.

How this bulletin compares to other ExAC references

This is a short, focused technical update. The references below sit alongside it on Examitect's reading list. The table helps you decide which document answers which kind of question so you are not searching two references at once on exam day.

ReferenceWhat it is forHow this update relates
Fire Resistance of Gypsum Board Wall Assemblies (NRC, this page) Tested assembly principles and design rules for FRR in gypsum-board partitions. The vocabulary anchor for partition fire performance. Read this first to understand the principles, then use the NBC for the code-required numbers.
Control of Sound Transmission through Gypsum Board Walls (NRC) STC ratings for the same families of gypsum-board partitions from the same research program. Companion bulletin. The two share wall families, authors, and funding partners. An acoustic fix can conflict with a fire fix; reading both back to back shows where the trade-offs land.
Guide for Sound Insulation in Wood Frame Construction (NRC) STC and IIC ratings for wood-frame walls and floors. Section 3 supplementary alongside this bulletin. Adds floor-ceiling assemblies that the two gypsum-board bulletins do not cover.
NBC 2020 Part 3 and Part 9 Code-required fire-resistance ratings: Subsections 3.1.7, 3.1.8, and the listed Part 9 assemblies in Subsection 9.10.3. Sets the code minimums. The NBC's listed assemblies trace back to the NRC research summarized in this bulletin. Pair the two on every fire-rating question.
CHING (Building Construction Illustrated) Visual reference for wall sections, assemblies, and building science across Sections 1 and 3. CHING shows how a wall goes together in section drawings. This NRC update tells you what each version of that wall is worth in fire-resistance minutes and which construction detail changes the outcome.
CHOP (Canadian Handbook of Practice) Practice reference for assemblies, construction documents, and site administration in Sections 1, 3, and 4. CHOP covers the architect's responsibilities around fire separations and listed assemblies. This NRC bulletin supplies the underlying assembly behaviour that informs those practice decisions.

How Examitect reinforces gypsum-wall fire ratings

Reading the bulletin gets you most of the way. The other part of the work is recognizing party-wall patterns under timed exam conditions. Examitect's question bank includes scenario questions on Type-X versus regular board, resilient channel placement, rock fibre installation quality, load-bearing versus non-load-bearing behaviour, and the listed assemblies in NBC Subsection 9.10.3. Each answer explanation links to the relevant NRC finding or code clause so you can re-read just the few pages you need rather than the whole bulletin again.

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

FAQ

NRC fire resistance FAQ

Fire Resistance of Gypsum Board Wall Assemblies is Construction Technology Update No. 2, a short technical bulletin written by M.A. Sultan and G.D. Lougheed and published by the National Research Council of Canada's Institute for Research in Construction in January 1997. It summarizes results from an industry-supported research project that tested 22 gypsum-board wall assemblies to determine how board type, layer arrangement, insulation, resilient channels, and stud configuration affect the fire-resistance rating of multi-family walls.

It is a supporting reference Examitect recommends, not one the ExAC Preparation Guide names. It maps to Section 2 fire safety (5.2.2 for Part 3 buildings and 5.3.2 for Part 9 buildings) and to Section 3 Assemblies and Detailing (8.3). It sits alongside Control of Sound Transmission through Gypsum Board Walls and Guide for Sound Insulation in Wood Frame Construction, the three NRC bulletins that together cover the fire and sound performance of Canadian gypsum-board partitions.

Fire-resistance ratings depend on the whole assembly, not just the gypsum board. The biggest gains come from rock fibre insulation installed tightly in the cavity, Type-X gypsum board in two layers, and resilient channels placed on the side away from the fire. The research fed directly into the 1995 National Building Code, which expanded the listed fire-rated wall assemblies in Part 9 from 17 in the 1990 Code to more than 160.

A fire-resistance rating (FRR) is the time in minutes that an assembly resists failure under a standard fire test, measured per CAN/ULC-S101. Failure means structural collapse, exceeding a specified temperature on the unexposed side, or letting flames or hot gases through. The National Building Code does not list FRRs below 45 minutes, so any tested assembly under 45 minutes is treated as having failed for code purposes.

Yes. Rock fibre insulation installed tightly between studs raised the FRR of a non-load-bearing assembly by 60 percent, from 60 to 100 minutes, compared to the same insulation installed loosely. Glass fibre and wet-sprayed cellulose did not change the FRR of non-load-bearing asymmetrical steel-stud walls. Installation quality matters as much as material choice, and the architect's specification should address both.

On the side of the wall away from the fire, which in a 1x2 asymmetrical load-bearing assembly is the double-layer side. The NRC tests showed an 11 percent better FRR when channels were on the double-layer side compared to the single-layer (fire-exposed) side. Placing channels on the fire-exposed side can significantly decrease fire performance because the gap they create acts as a passageway for hot gases.

It is a four-page bulletin, so a careful read takes under an hour. Focus on the seven Basic Wall Configurations diagram, the influence of each parameter (board type and density, layer count, channels, insulation, studs), and the difference between load-bearing and non-load-bearing behaviour. Pair it with NBC 2020 Subsections 3.1.7 and 3.1.8 and with the companion Control of Sound Transmission through Gypsum Board Walls bulletin.

No. The ExAC focuses on architectural decisions, not fire-engineering calculations. Expect questions that ask which assembly choice raises or lowers the rating, which detail an architect would flag during construction review, and which assembly meets a code-required FRR for a particular occupancy. You will not be asked to derive an FRR from first principles or apply Appendix D calculations.

The bulletin predates NBC 2020 but the underlying assembly principles have not changed. The research fed the FRR tables introduced in the 1995 NBC and remains the basis for how Canadian designers think about gypsum-board partition fire resistance. Always pair the reading with current NBC 2020 Part 3 and Part 9 fire-resistance provisions and with the current CSA gypsum board standards for code-compliant numbers.

Keep exploring

Other ExAC reference books.

Fire Resistance of Gypsum Board Wall Assemblies is one of many supporting references Examitect recommends. The 2026 ExAC Preparation Guide names four primary reference documents: CHOP (2020 edition), the IAP, NBC 2020, and NECB 2020. Examitect's core reading list below adds CHING, RSMeans, and Yardsticks.

CHING

Building Construction Illustrated. The visual reference for assemblies, materials, and detailing across Sections 1 and 3.

CHOP

Canadian Handbook of Practice. The Royal Architectural Institute of Canada's practice reference covering Sections 1, 3, and 4.

NBC 2020

National Building Code of Canada. Part 3 and Part 9 carry the fire-resistance ratings and fire separation provisions.

NECB

National Energy Code of Canada for Buildings. Covers the envelope and energy provisions in Section 2.

RSMeans

Construction cost data. Used for elemental estimating and cost-management questions in Section 1.

Yardsticks

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

Supporting references

Examitect's extended reading list of supporting references that appear across the ExAC topics, including the companion NRC bulletins on sound transmission.