Fire Separations & Fire Resistance Ratings

140 C above its initial temperature and preventthe temperature rise on the unexposed surfaceat any individual point greater than 180 C.The fourth criterion is only used for walls that must havea fire-resistance rating of one hour or more. The assembly shall prevent the passage of a hosestream through the assembly.This fourth criterion is intended to ensure a minimumresistance to the cooling and erosion effects of a hosestream that might be directed at the wall duringfirefighting. An assembly is first tested to determine itsfire-resistance rating; a duplicate assembly is thentested for half the desired fire-resistance rating time toa maximum of one hour and then subjected to a hosestream.Horizontal assemblies such as floors, ceilings and roofsare tested for fire-resistance from the underside only.This is because a fire in the compartment belowpresents the most severe threat to horizontalassemblies. Horizontal assemblies, when tested, aresubjected to a superimposed load. The test standardrequires that the size of the test floor or roof assemblymust be at least 16.8 m2 (180 ft2) with neither the lengthnor the width less than 3.66 m (12 ft).Firewalls and interior vertical fire separations such asinterior wall assemblies are tested on each side unlessthey are symmetric, in which case they only need to betested from one side. Exterior walls only need to betested from the inside. The test wall assembly issubjected to a superimposed load if the assembly designis intended to be used structurally. The test standardrequires that the size of the test wall assembly must beat least 9.3 m2 (100 ft2) with neither the width norheight less than 2.75 m (9 ft).Superimposed Loads During TestingIf the member or assembly design is to be loadbearing,such as a floor assembly, a load equal to the fullspecified load (ie., the specified gravity loat thatproduces a factored load effect as close as practicable tothe factored resistance of the test specimen)determined by the applicable design standard istypically applied. If conducted under a reduced load(i.e., a restricted load use condition), the test reportmust include the load applied, which may influencewhether a test result is accepted by a regulator for aparticular situation. (See also the CWC Fire Fact Sheetentitled “Fire Resistance Ratings of Light-weight Woodframe Assemblies and Loading in Canada.”)Standard Fire ExposureIn the standard fire-resistance test, the fire exposure iscontrolled by following a prescribed temperature profileinside the furnace as a function of time. The firetemperatures are typically produced inside the furnaceusing premixed burners that mix propane or natural gaswith air. The fuel mixture burns inside the furnace andthe amount of fuel is controlled so that the temperatureinside the furnace follows the time/temperaturerelationship shown in Figure 1 as closely as possible.Figure 1. Standard fire resistance test furnace temperature as a function of time.544

Fire Separation and Fire-resistance RatingRequirements in the NBCThe application of specific fire separation and fireresistance rating requirements in the NBC depend onmany factors, including the following: building area; building height; general occupancy type, as well as specific use ofa compartment/space; whether sprinklers are to be installed; number of streets the building faces, when thebuilding is not sprinklered; and, whether the construction type to be used ispermitted to be combustible or required to benoncombustible construction.The main requirements for fire-resistance ratings arefound in Subsection 3.2.2. of the NBC, which providesdetailed requirements for the height and area ofbuildings that are acceptable solutions in Division B. Asan example, the following are some generalizations toprovide some insight into required fire-resistanceratings for buildings containing only Group C residentialoccupancies: resistance rating not less than that required forthe supported assembly. Therefore, if a floorassembly requires a one-hour fire-resistancerating, the loadbearing walls or columns thatsupport the floor assembly must also have a onehour fire-resistance rating.In addition to the prescribed fire-resistance ratingsrequired for floor and roof assemblies and for thestructure supporting floors and roofs in 3.2.2., other fireseparations with fire-resistance ratings may be requiredwithin a building or floor area. For example, a fireseparation with a one-hour fire-resistance rating isrequired between suites of residential occupancy(Article 3.3.1.1., Division B, NBC); there are also variousminimum fire-resistance rating levels required for fireseparations between major occupancies, such as a onehour fire-resistance-rated fire separation betweenGroup C and Group D major occupancies (Article3.1.3.1., Division B, NBC).Methods for Determining Fire-resistanceRatingsSince full-scale fire-resistance tests are very expensive,they are not typically an option available to designers.Therefore, designers must have access to informationthat allows them to design fire-resistance-ratedstructural members and assemblies. In addition toindividual test reports provided by manufacturers ofproducts, this information can be found in the NBC, indesign listings published by listing/certificationorganizations such as UnderwritersLaboratories of Canada (ULC) andIntertek, in publications by manufacturersor industry associations, and throughstructural design standards used inCanada and other countries. Below arethe most commonly used sources fordesigning fire-resistance-rated assembliesand structural members for woodconstruction.For combustible construction up to three storeys,a 45-minute or one-hour fire-resistance ratingmay be required for the floor assemblies that arefire separations depending on the size of thebuilding.For larger buildings of combustible ornoncombustible construction builtto six storeys, a one-hour fireresistance rating is required forfloor assemblies that are fireseparations.For noncombustible constructionover six storeys, a two-hour fireresistance rating is required forfloor assemblies that are fireseparations.Roof assemblies may or may notneed a fire-resistance rating notless than that of the floorassemblies.In each case, the loadbearingwalls, columns or arches thatsupport floor and roof assembliesStandard fire resistance test of anthat are required to have a fire- exterior lightweight wood-frame wallresistance rating must have a fire- assembly.www.cwc.ca 613.747.5544 2019Test ReportsOver the last 25 years, a number of largeresearch projects7,9,10,11 focused on fireresistance and sound transmission havebeen conducted at the National ResearchCouncil of Canada (NRC) for lightweightwood-frame wall and floor assemblies. Aswell, some mass timber fire-resistance55

testing has been completed by the wood industry,particularly on wall and floor assemblies of crosslaminated timber.12,13,14,15,16The NRC research reports and commercial test reportsprovide test results that can be of use to designers.Generic Fire and Sound Resistance Tables in NBCThe information generated by the NRC research into thefire resistance of lightweight wood-frame assemblieshas been used to provide major additions to the Fireand Sound Resistance of Walls and the Fire and SoundResistance of Floors, Ceilings and Roofs Tables in theNBC (Tables 9.10.3.1.-A and -B, respectively). Thesetables are intended to provide designers of buildingsthat fall within Part 9 of Division B of the NBC with manyoptions to meet the fire-resistance rating and soundtransmission class requirements using generic materials.An example of the tables is provided in Figure 2.While Part 3 of Division B of the NBC does not directlyreference Tables 9.10.3.1.-A and -B, the fire-resistanceratings listed were determined on the basis of the testsconducted by NRC in conformance with the NBCreferenced fire test standard, CAN/ULC-S101, and that,therefore, are applicable to all building sizes.Component Additive Method in the NBCThe Component Additive Method was developed in theearly 1960s based on the analysis of fire-test data forType of Wall Wood Studs Single Row Loadbearingor NonLoadbearingW1aW1bW1cW1dW1elight-frame wall, floor and roof assemblies. Theestimated fire-resistance ratings tend to be conservativesince the assigned ratings must apply to all systems andproducts covered by the material standard description,as well as all the combinations of elements permitted bythe methodology. The assemblies must conform to allrequirements in the NBC Appendix D-2.3. for the ratingdeveloped using the method to be valid.TheComponent Additive Method can be used to assign afire-resistance rating of up to 90 minutes.The method received a significant revision and update inthe 2015 edition of the NBC, using the NRC researchdata into lightweight wood-frame assemblies. Themethod now can be used for wood-frame walls(loadbearing and non-loadbearing); wood-frame floorassemblies with wood joists, wood I-joists and threeFire-Resistance Rating(2)(3)WallNumberW1For more information on the component additivemethod in Appendix D-2.3. of the NBC, the method forglulam beams and columns in Appendix D-2.11. of theNBC, and the mass timber methodology in Annex B ofCSA O86, including examples of the calculations andbeam, column and CLT panel (floor, roof and wall)selection tables for fire resistance, see Chapter 10 ofthe CWC Wood Design Manual.Description38 mm x 89 mm studs spaced 400 mm or 600 mm o.c.with or without absorptive material1 layer of gypsum board on each sideW1 with 89 mm thick absorptive material(6) 15.9 mm Type X gypsum board(7)W1 with 89 mm thick absorptive material(6) 12.7 mm Type X gypsum board(7)W1 with 89 mm thick absorptive material(6) 12.7 mm regular gypsum board(7)(9)W1 with no absorptive material 15.9 mm Type X gypsum board(7)W1 with no absorptive material 12.7 mm Type X gypsum board(7)LoadbearingNonLoadbearingTypical SoundTransmissionClass(2)(4)(5) 1h1h3645 min[1 h(6)]45 min[1 h(8)]3430 min30 min[45 min(8)]321h1h3245 min45 min32Figure 2. Extract of generic tables in NBC taken from Table A-9.10.3.1.-A.66

types of wood trusses, including metal-plate-connectedwood trusses; and, wood-framed roof assemblies ofwood joists and metal-plate-connected wood trusses(both pitched and parallel chord design). There areminimum size requirements for the wood framingmembers (Appendix D-2.3.6.).In general, when applying the CAM, the fire-resistancerating of an assembly is calculated by adding: the time assigned to the protective membranes(typically, gypsum board) on the fire side; the time assigned to the structural framingmembers; the time allowed for any additional protectivemeasures, such as the inclusion of insulation orreinforcement for a membrane, if applicable;and, the time reduction required in some instances,such as when resilient metal channels areinstalled with a single layer of gypsum board in aloadbearing wall assembly.It is important to understand that the CAM has beencalibrated based on test data and that the timesassigned to individual components cannot be used topredict the fire-resistance rating of an assembly that isnot explicitly included in the method as published in theNBC.Proprietary ListingsA multitude of fire-resistance tests have beenconducted over the last 80 years by North AmericanLaboratories. In some cases, results are availablethrough design listing services provided by certificationorganizations, such as: Intertek PFS TECO Underwriters Laboratories of Canada / UnderwritersLaboratoriesIn addition, manufacturers of construction productspublish results of fire-resistance tests on assembliesincorporating their proprietary products, such as theGypsum Association’s Fire Resistance Design Manual.17Heavy Timber ConstructionHeavy timber construction is a type of mass timberconstruction that is specifically recognized in the NBC. Adegree of fire safety is attained by placing limitations onthe minimum sizes of wood structural members and onthe thickness and composition of wood floors and roofsand by the avoidance of concealed spaces under floorsand roofs. Heavy timber construction, including varioustypes of connections, following the requirements inArticles 3.1.4.6 and 3.1.4.7 of the NBC are allowed to beused when combustible construction is permitted and isnot required to have a fire-resistance rating more than45 minutes. The heavy timber construction type onlypermits the use of solid-sawn wood and gluedlaminated timber (glulam) members. Minimum sizes forheavy timber floor and roof assemblies and the othertype of structural elements are described in Article3.1.4.7. The minimum dimension requirements of heavytimber beams, columns, and other similar structuralelements are summarized in Table 1. The different typesof heavy timber connections are described in Article3.1.4.7 and are not otherwise required to have a fireresistance rating and therefore need not be protected.Several of these connections are shown in Figure 3. Inmany cases described within the heights and areasArticles of Subsection 3.2.2 of the NBC, ible supports (e.g. beams and columns)without a fire-resistance rating can be used to supportheavy timber assemblies.Table 1. Minimum dimensions for wood members to be considered heavy timber construction.Solid Sawn(width x depth),mm x mmGlued-laminated(width x depth),mm x mmRound(diam),mmColumns140 x 191130 x 190180Arches supported on the tops of walls or abutments89 x 14080 x 152-Beams, girders and trusses89 x 14080 x 152-Arches supported at or near the floor line140 x 140130 x 152-Floors,Columns191 x 191175 x 190200floors plus roofsBeams, girders, trusses and arches140 x 241 or191 x 191130 x 228 or175 x 190-SupportedAssemblyRoofs onlyStructural ElementSource: 2015 National Building Code of Canada, Division B, Table 3.1.4.7.www.cwc.ca 613.747.5544 201977

Figure 3. Examples different types of heavy timber connectionsCalculation of Glulam Fire-resistance Ratings inAppendix D of the NBCA calculation procedure to calculate the fire-resistancerating of glulam beams and columns can be found inAppendix D under Section D-2.11., Division B of the NBC.The empirical equations are based on the reducedproperties method and validated by fire-resistancetests. The reduced properties method is based on thefact that large wood members (exposed to the ‘standardfire exposure’ - see above) burn slowly at a rate ofapproximately 0.6 mm per minute and the insulatingeffects of the char layer protects the unburned portionof the wood from significant temperature rise. Theequations provide provisions for calculating the fireresistance rating of glulam beams and columns exposedto fire from three or four sides. The methodology takesinto account the size of the glulam member, the ratio ofthe factored load to the factored resistance and theslenderness of the beam or column.Calculation of Fire-resistance Ratings for MassTimber Elements in CSA O86In the 2014 edition of the Canadian Wood Designstandard CSA O86,18 a revised calculation procedure fordetermining the fire-resistance rating of large timbermembers was added as Annex B. The procedure isapplicable to solid-sawn timbers, glulam, structuralcomposite lumber (SCL) members, and cross-laminatedtimber (CLT) wall and floor assemblies. The method canalso be applied to any structural members as opposedto being restricted to those subjected to simplysupported beams in bending or columns in simple axialcompression. For instance, the CSA O86 method can beapplied to members in tension, axial members witheccentricity or lateral loads, and continuous beamsextending over multiple supports. However, while theNBC Appendix D-2.11. method is considered anacceptable solution for calculating fire resistance, theCSA O86 Annex B method is considered an alternativesolution, since it is not directly referenced at this time inthe NBC for determining the fire resistance of woodmembers.Engineering JudgmentIn some cases, the alternative methods described todetermine fire-resistance rating of an assembly orstructural member are not sufficient. An engineer maydecide to propose an alternative solution to meet thefire-resistance requirements using another approachsuch as engineering judgment. In this case, it is up tothe regulatory authority whether they will accept thetechnical justification used to support the alternativesolution.88

The standard test method to determine fire-resistanceused in the United States is ASTM E 119, “Fire Tests ofBuilding Construction and Materials”,19 which is verysimilar to CAN/ULC-S101. The two test methods providethe same fire exposure and in many cases produce thesame results.Given the close similarity in teststandards, the guide ASTM E 2032, “Extension of Datafrom Fire Resistance Tests Conducted in Accordancewith ASTM E 119”,20 is a valuable source of informationwhen extrapolating test results to assemblies that havenot been tested but are close to an assembly that hasbeen tested. The guide is in part based on Dr. TiborHarmathy’s The Ten Rules of Fire Endurance, whichprovides guidance on the impact made on the fireresistance rating of materials and assemblies when theoriginal product or assembly is altered in some way.Sometimes it is necessary to determine the fireresistance of an assembly when exposed to a nonstandard fire exposure such as in performance-baseddesign. In these cases, a designer may use a computerheat transfer model using the design fire to determinethe exposure. This will allow the designer to predict acharring rate in the wood and thereby predict theremaining capacity of the structural member as afunction of time.FirewallsA firewall is a very special type of fire separation with afire-resistance rating. It performs the function ofseparating adjoining buildings sharing a common lot lineor separating a single building into two or moreseparate buildings on the same property. The firewall isused to protect the adjoining building for as long as ittakes a fire to burn itself out. Depending on theoccupancy it separates, a firewall may require a fireresistance rating of two or four hours.The following definition is provided by the NBC:A firewall is defined as “a type of fire separationof noncombustible construction that subdivides abuilding or separates adjoining buildings to resistthe spread of fire and that has a fire-resistancerating as prescribed in the NBC and hasstructural stability to remain intact under fireconditions for the required fire-rated time.” a firewall required to have a fire-resistance rating of two hours need only be constructed usingnoncombustible construction, while a firewallrequired to have a fire-resistance rating great

Fire separations and fire-resistance ratings are often required together but they are not interchangeable terms, nor are they necessarily mutually inclusive. The National uilding ode of anada (N )1 provides the following definitions: A fire separation is defined as “a construction assembly that acts a