Fire resistance of gypsum board walls

Placeholder page for the supporting reference Fire resistance of gypsum board walls, part of the Examitect reading list for the ExAC.

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The NRC fire-resistance update at a glance

Here's the at-a-glance summary an Intern Architect can scan before opening the PDF.

Full titleFire Resistance of Gypsum Board Wall Assemblies
AuthorsM.A. Sultan and G.D. Lougheed, senior fire research officers at the National Fire Laboratory of the NRC Institute for Research in Construction
PublisherNational Research Council of Canada, Institute for Research in Construction (IRC)
Series and numberConstruction Technology Update No. 2, ISSN 1206-1220
PublishedJanuary 1997
LengthShort bulletin (four pages of body content)
LanguagesEnglish (the NRC Publications Archive also lists French equivalents for many Construction Technology Updates)
Primary audienceArchitects, engineers, builders, and code authorities working on multi-family residential construction in Canada
ExAC relevanceSupplementary on Examitect's ExAC study plan for Section 2 categories 5.7 through 5.10 (Fire and Life Safety under the NBC) and Section 3 category 8.3 (Assemblies and Detailing). Sits beside the companion NRC bulletins on sound transmission.
Where to accessNRC Publications Archive, free download (DOI 10.4224/40002869). The document is in the public technical literature, not a paywalled standard.

Why this update 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 the listed FRR survive contact with a real construction site. Examitect's ExAC study plan lists this bulletin behind several Section 2 categories where the NBC supplies the rules and architects supply the assemblies.

The plan lists the Update as a supplementary reference for four Section 2 categories: 5.7 fire protection and life safety principles, 5.8 means of egress, 5.9 occupant load and exiting, and 5.10 fire protection systems. It also appears under Section 3, category 8.3 (Assemblies and Detailing), as the partition-wall companion to the NRC's two sound-transmission bulletins. The three together form the Canadian foundation for partition-design questions on the exam.

You will not be asked to derive an FRR. You will be asked which detail compromises a listed assembly, which fix an architect would specify when a site condition threatens a fire separation, and how a single-fix change (board type, channel location, insulation tightness) moves the rating up or down.

ExAC sections this reference supports

Section 1
Section 2
Section 3
Section 4

What the NRC update is

Fire Resistance of Gypsum Board Wall Assemblies is a four-page Construction Technology Update from the National Research Council's Institute for Research in Construction. It translates a much longer, industry-supported research project into a single bulletin a designer can read in under an hour. The funding consortium included Canada Mortgage and Housing Corporation (CMHC), the Canadian Sheet Steel Building Institute, the Cellulose Insulation Manufacturers Association of Canada, Forintek, the Gypsum Manufacturers of Canada, Owens Corning Fiberglas Canada, and Roxul.

The project tested 22 wall assemblies in NRC's propane-fired vertical furnace and rated each one based on the time it took to fail structurally, exceed a specified unexposed-side temperature, or let flames or hot gases through. The variables studied were the type, density, and thickness of the gypsum board, symmetrical and asymmetrical layer arrangements (1x1, 1x2, 2x2), wood and steel stud configurations, resilient channel location, and the type and installation of cavity insulation. The same research program included a companion acoustic study, summarized in Construction Technology Update No. 1, so that designers could see how fire and sound trade-offs interact in the same wall.

The findings fed directly into the 1995 edition of the National Building Code. The number of listed fire-rated wall assemblies in Part 9 jumped from 17 in the 1990 Code to more than 160 in the 1995 Code, and that expansion is the direct ancestor of the FRR tables you use in NBC 2020 today.

Inside the update, the wall systems tested

The bulletin organizes its 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.

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 and density. Resilient channels are not present, so the cavity insulation contributes directly to the rating.
Single wood studs with resilient channels 38 by 89 mm studs, 102 mm cavity, channels on one face Channel location is critical. Channels on the unexposed (double-layer) side raise the FRR; on the fire-exposed side they create a hot-gas pathway and can 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 does not improve FRR on its own. The acoustic benefit is real, but the fire-rating gain is not.
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; channels on the fire-exposed side can reduce it.
Double wood studs Two rows of 38 by 89 mm studs on separate plates set 25 mm apart, 203 mm cavity Full structural separation. Excellent for acoustics; no particular fire benefit from the staggered or double framing itself.
Non-load-bearing steel studs (64 mm) 31 by 64 mm steel studs, 600 mm on centre In 2x2 walls the type of stud is insignificant. Wood-stud 2x2 assemblies provided a slightly better FRR than steel-stud 2x2 assemblies. 1x1 was not tested because the assemblies did not meet STC criteria.
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 wall. Glass fibre or wet-sprayed cellulose insulation made no FRR difference in non-load-bearing 1x2 steel-stud assemblies.

Across all configurations, increasing from one to two layers of gypsum board 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 actually outperforms a 1x1 since the assumption does not apply.

Key terms every ExAC candidate should know

The exam reuses this vocabulary without redefining it. Learn the terms early so you spend exam time picking the answer, not parsing the question.

TermWhat it means
Fire-resistance rating (FRR)Time in minutes that an assembly resists structural failure, exceeds a specified unexposed-side temperature, or passes flames or hot gases under a standard fire test (CAN/ULC-S101 in Canada).
Type-X gypsum boardGeneric 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.
Regular gypsum boardStandard 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), and 7.82 kg/m².
Glass-fibre coreReinforcing fibre embedded in the gypsum core that holds the board together as it cracks under fire exposure. Raised the single-layer load-bearing FRR by 25 percent in the NRC tests.
1x1, 1x2, 2x2 layupsShorthand for layers of gypsum board on each side. 1x1 is one layer each face; 1x2 (asymmetrical) is one and two layers; 2x2 is two layers each face.
Resilient channelThin stepped steel strip about 25 mm wide. One leg fastens to the stud, the other to the gypsum board. Placement is critical: channels on the fire-exposed side can lower the FRR by creating a hot-gas pathway.
Rock fibre insulationMineral wool insulation. Tightly installed in the cavity, it raised non-load-bearing FRR from 60 to 100 minutes, a 60 percent gain. Loose installation kills the benefit.
Glass fibre insulationFibreglass batt insulation. Contributed to FRR in load-bearing walls with resilient channels. Had no FRR effect in non-load-bearing 1x2 steel-stud walls.
Load-bearing assemblyWall that carries structural load. A 1x2 performs like a 1x1 because fire is assumed to start on the single-layer (weaker) side.
Non-load-bearing assemblyPartition that does not carry structural load. A 1x2 outperforms a 1x1, since the fire-side assumption does not apply.
CAN/CSA-A82.27The Canadian standard regulating the use and application of gypsum board cited by the NRC tests. The CSA A82 series has been updated several times since 1991; check the current edition referenced by the NBC you're working with.

How the NRC update compares to other ExAC references

This bulletin is short and focused. The references below sit around it on Examitect's ExAC study plan. Use the table to decide which document answers which kind of question.

ReferenceWhat it's forHow this update relates
Fire Resistance of Gypsum Board Wall Assemblies (NRC)Principles and tested assembly families for FRR in gypsum-board partitions.The supplementary reference on this page. The vocabulary anchor for partition-wall fire performance.
Control of Sound Transmission through Gypsum Board WallsNRC bulletin on STC ratings for the same families of gypsum-board partitions.Companion document from the same research program. Tested on many of the same walls and reminds you that an acoustic fix and a fire fix can interact, sometimes against each other.
Guide for Sound Insulation in Wood Frame ConstructionNRC guide on STC and IIC for wood-frame walls and floors.Section 3 supplementary alongside this Update. Adds floor-ceiling assemblies that the fire and STC bulletins do not cover.
NBC 2020 Part 3 and Part 9Code-required fire-resistance ratings (Subsections 3.1.7 and 3.1.8) and listed Part 9 fire-rated assemblies (Article 9.10.3).Sets the code minimums. The NBC's listed assemblies trace back to this NRC research.
CHING (Building Construction Illustrated)Diagrammatic reference for assemblies and detailing.CHING shows the wall section drawings; this NRC update tells you what each version of the wall is worth in fire-resistance minutes.
CHOP, Chapter 5.4 and 6.4Practice reference for assemblies and construction documents.CHOP covers the architect's responsibilities around fire separations and listed assemblies. This NRC bulletin supplies the underlying assembly behaviour.

How to study the NRC update for the ExAC

  • Anchor on the Basic Wall Configurations diagram. The seven figures on page 3 name every wall family tested. Recognize them by shape (single, staggered, double, steel; with or without channels) before you read the parameter analysis.
  • Learn how each parameter moves the FRR. Six variables matter: board type, density, layer count, board thickness, resilient channel placement, and insulation type and installation. Know the direction and rough magnitude for each.
  • Memorize the rock fibre rule. Tightly installed rock fibre in a non-load-bearing wall raised the FRR from 60 to 100 minutes, a 60 percent gain. Loose installation kills the benefit. This single fact answers more than one exam question.
  • Internalize the channel-placement rule. Channels on the fire-exposed (single-layer) side of an asymmetrical wall reduce FRR. Channels on the unexposed (double-layer) side raise it.
  • Distinguish load-bearing from non-load-bearing behaviour. In load-bearing walls a 1x2 performs like a 1x1; in non-load-bearing walls a 1x2 outperforms a 1x1. Mixing these up is a common exam trap.
  • Cross-reference NBC 2020 Part 3 and Part 9. Read the bulletin next to Subsections 3.1.7, 3.1.8, and Article 9.10.3. The code's listed assemblies are direct descendants of this research.

ExAC sections this update supports

The table below shows where the bulletin shows up on Examitect's ExAC study plan and how it backs adjacent categories.

ExAC sectionWhere this update appears on Examitect's study plan
Section 1
Design and analysis		Indirect. Useful background for engineering coordination and schematic decisions on multi-unit residential projects, but not listed on Examitect's study plan for any Section 1 category.
Section 2
Codes		Listed as a supplementary reference for categories 5.7 (fire protection and life safety principles), 5.8 (means of egress), 5.9 (occupant load and exiting), and 5.10 (fire protection systems). The main exam use case.
Section 3
Sustainability and final project		Listed as a supplementary reference for category 8.3, Assemblies and Detailing. Pairs with CHING Chapters 3 to 8 and 10 and with CHOP Chapters 2.5, 5.4, and 6.4.
Section 4
Construction and practice		Indirect. Helps with construction-review judgment when site conditions threaten a fire separation, such as missed Type-X layers, loose rock fibre, or channels installed on the wrong face.

Tips for Intern Architects reading the update

This is one of the shorter documents on Examitect's ExAC study plan. The reading is quick; the trick is remembering the right details under exam pressure.

Tip 1, start with the figure on page 3. The Basic Wall Configurations diagram is the spine of the bulletin. Every other page references one of those seven framing families. Spend a few minutes naming them by shape before you read the body.

Tip 2, lock in the channel-placement rule. 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.

Tip 3, remember the rock fibre number. Tight rock fibre, 100 minutes. Loose rock fibre, 60 minutes. Same wall, same insulation, different installation. Specifications and site supervision win FRR points the test laboratory cannot.

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.

Tip 5, do not confuse acoustic gains with fire gains. Staggered studs and double studs help STC but not FRR. An asymmetrical 1x2 layup raises STC but does nothing for the load-bearing fire rating. Trade-offs are the whole point of reading the two NRC bulletins back to back.

Tip 6, read it next to NBC 9.10. The Update predates NBC 2020, but its tested assemblies are the ancestors of the listed assemblies in Article 9.10.3. Cross-checking the two cements the FRR numbers and the underlying principles together.

Tip 7, pair the reading with the sound transmission bulletin. Update No. 1 (sound) and Update No. 2 (fire) come from the same research program. Reading them in sequence shows you which design moves help both, which help one and hurt the other, and which are neutral.

Common ExAC scenarios where this update is the answer

The scenarios below show up in different wording across ExAC sittings. If you recognize the pattern, the NRC findings tell you how to think about the answer.

  • 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 why?
  • 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 fire-resistance impact and what is the architect's response?
  • A duplex switches from Type-X to regular gypsum board to save cost. Which listed assemblies in NBC Article 9.10.3 no longer apply?
  • A multi-residential project has a load-bearing 1x2 party wall and the team proposes adding the extra layer to the fire-exposed side instead of the unexposed side. Why does this change matter?
  • A contractor wants to substitute glass fibre for rock fibre in a non-load-bearing 1x2 steel-stud wall to save money. What does the NRC research say about the FRR impact?
  • A multifamily wall must meet both an STC of 50 and an FRR of 1 hour. Which combination of resilient channels, insulation, and gypsum-board layers achieves both targets without trading one off against the other?
  • A renovation increases gypsum-board thickness from 12.7 mm to 15.9 mm Type-X in a load-bearing 1x2 wall with channels on the fire-exposed side. Does the FRR improve?

Each scenario maps back to a specific NRC finding: channel placement, insulation installation, board type, layer count and direction, or material substitution. Read the bulletin once with these scenarios in mind and the connections cement quickly.

How Examitect reinforces gypsum-wall fire ratings

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

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.

NRC fire resistance and ExAC 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 supplementary reference on Examitect's ExAC study plan. The plan lists it under Section 2 categories 5.7 through 5.10 (Fire and Life Safety under the NBC) and under Section 3 category 8.3 (Assemblies and Detailing). 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 matters as much as material type, and the architect's specification should call out 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 supplementary references on Examitect's ExAC study plan. The core reading list runs through the six primary references below.

CHING

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

CHOP

Canadian Handbook of Practice. The RAIC's practice reference covering most categories in Sections 1, 3, and 4.

NBC 2020

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

NECB

National Energy Code of Canada for Buildings. Supports the envelope and energy questions in Section 2.

RSMeans

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

Supporting references

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