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p1ann1ng report BUILDING CONSTRUCTION INFORMATION FROM THE CONCRETE AND MASONRY INDUSTRIES

NO. 168 OF A SERIES

Guide to BOCA/NBC Requirements for Concrete and Masonry Fire Walls

Introduction Properly designed and constructed fire walls provide an effective means of stopping or controlling the spread of fire. A generic definition of the term "fire wall" is "a wall of sufficient durability and stability to withstand the effects of the most severe anticipated fire exposure."<1> In addition, any openings in the wall, if allowed, must be protected.

The BOCA National Building Code (hereafter referred to as BNBC or "the code") recognizes areas separated by fire walls as being separate buildings. Insurance underwriters also acknowledge this by applying rates individually to each fire area when fire walls used in compartmentation are constructed of concrete or masonry.

Fire walls must meet fire-rating requirements of the code in accordance with ASTM E 119 test procedures.<2> Structural and other requirements of the code must also be considered in fire-wall design, but these are outside the scope of this report. The text that follows will gen­erally focus only on the fire-related provisions of the code applicable to concrete and masonry fire walls, based on the 1987 edition of the BNBC.<3>

Purpose The purpose of this report is to provide buildfng officials and the design community with information on the code requirements germane to concrete and masonry fire walls.

The report contains 1. The code's definition of a fire wall and characteristics

common thereto 2. Fire-rating requirements for fire walls and their com­

ponents (parapets, opening protectives, and so forth) 3. Conceptual drawings of wall-roof connections and

restraining conditions necessary for fire walls to meet the code's stability criterion during a fire

Concrete, clay-brick, and concrete masonry (top, middle, bottom) fire walls provide excellent barriers for containing the spread of fire from one side of the wall to another.

Common Characteristics of Fire Walls In general, fire walls share the following characteristics : 1. Areas divided by them are considered separate

buildings 2. The number needed in a structure is generally gov­

erned by height and area restrictions that are based on occupancy and construction type

3. All openings in fire walls must be protected by appro­priate fire-rated assemblies

What Is a Fire Wall? The BNBC defines a fire wall as follows:

Fire wall-a fireresistance-rated wall, having protect­ed openings, which restricts the spread of fire and extends continuously from the foundation to or through the roof.* Section 908.1 further expands on the definition: (Fire] walls shall have sufficient structural stability under fire conditions to allow collapse of construction on either side without collapse of the wall, and shall be constructed of any approved noncombustible ma­terials providing the required strength and fireresis­tance rating specified in Table 401 for the type of construction, but not less than the fire grading of the use group specified in Table 902.* Additional requirements for fire walls are provided in

other subsections of Section 908.0 of the code. Appli­cable subject matter includes cutting of walls, hollow walls, combustible insulation, continuity of walls , and offset fire walls.

Structural strength and stability requirements are found in Articles 11 and 21 but are outside the scope of this report.

Fireresistance Requirements The required fire-endurance rating of a fire wall is a function of construction type and use group. Ratings based on construction type are indicated in Table 401 . Use-group requirements are referenced by this table

and specified in Table 902. The more severe of the two requirements dictates the assembly 's minimum fire­resistance rating. Requirements from these tables per­taining to fire walls are shown here in Tables 1 and 2. Thicknesses of concrete and masonry wall assemblies corresponding to these ratings can be determined from Fig. 1, Table 3, or Table 4 accordingly.<41

4 ~~~~~~~----+-----

~ .; 3

" c: e :::0 '0 c:

"' ~

2 u::

O L-~------~------~----~------~----~ IV:Z 2 3 4 5 6 7

Panel thickness, in.

Note: Fig. 1 is referenced in Section 903.1 .1 of the BOCA Code, 1987.

Fig. 1. Thickness of concrete required for fire endurances shown.

*Copyright 1986 BOCA International. All rights reserved. Published by arrangements with author.

Table 1. Fireresistance Ratings of Structure Elements, in Hours* Type of construction , Section 401.0

Noncombustible Noncombustible/Combustible

Type 1 Type2 Type3 Type4 Section 402.0 Section 403.0 Section 404.0 Section 405.0

Structure element, Protected Protected Unprotected Protected Unprotected Heavy timber, note a note b

1A I 18 2A I 28 2C 3A 38 4

1. Fire walls and party walls 4 I 3 2 I 2 2 2 2 2 Section 906.0 Not less than fire g radin g of use rou g p( see Table 902 or Table 2, a e 3 here p g

Note a. For increased fireresistance-rating requirements in special high-hazard uses involving a higher degree of fire severity and higher concentration of combustible contents, see Section 600.2. For fireresistance-rating requirements for structural membranes and assemblies that support other fireresistance-rated members or assemblies, see Section 912.1.

Note b. For substitution of other structural materials for timber in Type 4 construction, see Section 1702.2.

*Copyright 1986 BOCA International. All rights reserved. Published by arrangements with author.

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When Are Fire Walls Required? Height and area limitations, based on the occupancy and type of construction, govern the number of fire walls required within a given structure. For new construction , areas and heights of all buildings and structures be­tween exterior walls, or between exterior walls and fire walls, must not exceed the limits specified in Table 501 of the code (not shown here).

The tabular height and area values may be modified by Sections 501 , 502, 503, 504, and notes to Table 501.

Mixed Occupancies Where different use groups occur on either side of a fire wall, the fire-endurance rating of the wall shall be the high­er of (1) the value from Table 401 (Table 1 here) based on

Table 2. Fire Grading of Use Groups*

Use group

A-1 Assembly, theaters A-2 Assembly, night clubs A-3 Assembly, recreation centers, lecture

halls, terminals, restaurants A-4 Assembly, churches B Business E Educational F Factory and Industrial H High hazard

1-1 Institutional, residential care 1-1 Institutional, incapacitated 1-3 Institutional, restrained M Mercantile

R-1 Residential, hotels R-2 Residential, multifamily dwellings R-3 Residential, 1- and 2-family dwellings S-1 Storage, moderate hazard S-2 Storage, low hazard

Fire grading in hours

3 3

2 H'.l 2 H'.l 3 4 1 2 3 3 2 H'.l 1 3 2

"Copyright 1986 BOCA International. All rights reserved. Published by ar­rangements with author.

type of construction or (2) the higher value from Table 902 (Table 2 here) for each individual occupancy.

Fire-Wall Components In designing fire walls, important aspects to consider are structural stability, fireresistance rating require­ments, and the design and protection of integral wall components. Three of these components-parapets, openings, and penetrations-are discussed below.

Parapets and Wall Continuity A parapet is that part of any wall entirely above the roof line (see photo, front page). As an extension of a fire wall, its function is to prevent the spread of fire across the roof from one building to another. The code requires that the fire-wall parapet extend 2ft 8 in. above the roof surface. Where a noncombustible roof is present, the wall is permitted to terminate at the underside of the roof deck provided the roof is properly firestopped at the wall. Other exceptions are indicated in Section 908.5.2 of the code.

Table 4. Minimum Equivalent Thickness in Inches of Load­Bearing Concrete Masonry Unit Walls for Fireresistance Ratings

4 hour 3 hour 2 hour

Expanded slag or pumice 4.7 4.0 3.2 Expanded clay, shale, or slate 5.1 4.4 3.6 Limestone, cinders, or slag 5.9 5.0 4.0 Calcareous and siliceous gravel 6.2 5.3 4.2

Reproduced from Table 1405.6.1 of the BOCA Code, 1987. • Fire ratings for the thicknesses between tabulated values may be obtained by direct interpolation. BOCA- Walls composed of hollow concrete masonry units having a nominal thickness of 8 in. or greater and having a fire-resistance rating of at least two hours shall be classified as four hours when the hollow spaces are completely filled with insulation, grout, or a dry granular material such as expanded slag, clay, shale, or sand. •copyright 1986 BOCA International. All rights reserved. Published by arrangements with author.

Table 3. Fireresistance Periods for Load-Bearing Clay and Shale Brick Walls1

Combustible

TypeS Section 406.0

Protected Unprotected

SA 58

2 2

Nominal Ultimate fireresistance period in hours

wall Noncombustible members Combustible thick- Wall framed into wall or no members framed

ness, in. type framed-in members into wall

Plaster Plaster Plaster on

No on one on two No exposed plaster side2 sides2 plaster side2

4 Solid 1% 13/4 21!2 - -8 Solid 5 6 7 2 21!2

12 Solid3 10 10 12 8 9 12 Solid4 12 13 15 - -

9 to 10 Cavity 5 6 7 2 21!2

1BOCA references BIA "Building Code Requirements for Engineered Brick Masonry." Table 3 is a reprint from that standard.

2To achieve these ratings, each plastered wall face must have at least 'h-in., 1:3 gypsum-sand plaster. 3Based on load failure . •Based on temperature rise (for non-load-bearing walls).

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In a case where two buildings of different heights are separated by a fire wall, the code's criterion for a fire wall applies only to that part of the wall up to the point where the fire wall would normally terminate if both buildings were the height of the lower of the two.

The portion of the wall above the fire-wall termination point must comply with requirements in Tables 401 and 906.2 for exterior walls with zero fire-separation distance. Openings in the portion of the wall above the fire wall and within 15 feet vertically above the lower roof must be pro­tected in accordance with BNBC Section 906.5, unless the lower roof has a fireresistance rating of not less than one hour. This case is illustrated in Fig. 2.

Fire walls are required to be made smoke-tight at their junction with exterior walls, and in exterior wall construc­tion where studs are utilized, the fire wall shall extend through the stud space to the exterior sheathing.

Protected openings if law roof has less than l·hour f1re rating

15'

~Parapet (exterior wall requirement)

1-, 2-, 3-, or 4-hour fire- rated exterior wall

32"min. parapet

Fig. 2. BNBC fire-wall requirements for unequal building heights.

Openings Size Requirements. Provisions regulating openings in fire walls are specified in Section 909 of the code. Fire-wall openings must not exceed 120ft in area, and cumulatively, their width at any floor level shall not ex­ceed 25% of the length of the fire wall. An exception to the above applies to the first story that complies with Section 909.2.1 of the code.

Protection Requirements. Every opening in a fire wall shall be protected with an approved automatic opening protective assembly complying with BNBC Section 916.2 except as provided in Section 814.2.1 for horizontal exit openings.

Associated sections on specific types of opening protectives include

909.3.1 Hold-open devices 916.0 Fire-door assemblies 918.0 Fire dampers 919.0 Wired glass

It should be mentioned that wired glass in fire doors in fire walls is prohibited unless the door is used as a horizontal exit. In this case, the glass limitations are specified in Section 919.1.1 of the code.

Penetrations Where penetrations through fire walls are permitted, approved noncombustible materials must be installed to prevent the passage of flame and products of com­bustion through spaces in the wall, without decreasing the fireresistance rating or structural integrity of the wall. Firestopping must comply with the provisions specified in BNBC Section 921 .

Conceptual Design of Fire Walls In many ways, a fire wal is no different from other walls. It can be used in a nonstructural capacity or as a load­bearing and/or shear wall when designed to the struc­tural provisions of the code. When used as a shear or bearing wall, special attention must be paid to wall-roof connections such that the wall will still be able to meet the collapse criterion in Section 908.1 of the code. Types of connections and restraining conditions necessary to stabilize the fire wall against collapse during a fire are conceptually illustrated in Figs. 3, 4, and 5. Require-

7 Restramt of fire wall provided by roof diaphragm

Section view

Fig. 3a. Restraint condition of fire wall with nonyielding connections.

Resultant restraining force n roof diaphragm

......_ ~

Shear wall _./

\Area of roof Load-bearing failure f irewall~

Resultant force from failing roof ..-

Shear wall \

Plan view

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Fig. 3b. Plan view of forces acting during failure.

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~stra in! of fire wall provided by roof d iaphragm

Lood-beonng f ire wall

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Resultant force from collapsing roof pr1or

_ to collapse

Section view

Fig. 4a. Restraint condition of fire wall with yielding con­nections before roof collapse.

Roof

I Restraint of fire wall provided by roof diaphragm

Load-bearing f •re wa ll

I'

Roof foils due to loss of load-carrying capacity

~

Section view

Fig. 4b. Restraint condition of fire wall with yielding con­nections after roof collapse.

Resultant restraining force n roof diaphragm ~ ~

Shear wo II .J

~Area of roof

Load-bearing collapse

firewall --

lJ Resultant force from collapsing roof -

Shear wall '\

Plan view

Fig. 4c. Plan view of forces acting before roof collapse.

ments corresponding to fireresistance and fire-wall com­ponents are shown in Fig. 2.

Concrete and Masonry Wall Joints The rules that govern control-joint selection for interior concrete and masonry walls also apply to concrete and

Nonbeoring wa lls--~--"

Section view

Fig. 5a. Fire wall with no restraint at roof after collapse (free standing).

Non-lood-beormg Roof bears on fire wall extenor wall \

Area of collapsing roof~

Roof bears on

'-exterior wall \

Plan view

Fig. 5b. Fire wall with no restraint at roof before collapse (free standing).

masonry fire walls. Although this discussion is beyond the scope of the report, a number of publications are available on the subject.(5.6,7.BJ

Where tilt-up construction is utilized, joints between panels should be protected as shown in Fig. 6.<9J The figure specifies the minimum thickness of ceramic-fiber blankee required between wall panels to provide fire­resistance ratings up to four hours. Ratings are based on joint widths of % in. and 1 in. for a variety of panel thicknesses. Direct interpolation of the curves can be made for joint widths between 3AJ in. and 1 in.

Summary This report explains provisions from the BNBC specifi­cally pertinent to concrete and masonry fire walls. The text may be applicable to fire walls constructed of other materials but should not be assumed as such. In retro­spect, the key points regarding concrete and masonry fire walls can be summarized as follows:

' Ceramic-fiber blanket- a mineral wool insulation material made of alumina-silica fibers and weighing 4 to 10 lb per cubic foot.

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#-inch joint width

~ 2 r-----;------r----~------r---~ }>

Panel thickness, in.

l-inch maximum regardless of opening rat ing

Ceramic-fiber blanket

- Carbonate or siliceous aggregate concrete

-- Sand-lightweight or lightweight concrete

Fig. 6. Determination of joint thickness between precast concrete wall panels.

1. The function of a fire wall is to contain effectively the most severe anticipated fire for the duration of the assembly's rating period such that the fire does not spread from one side of the wall to the other.

2. Three characteristics of code-required walls are a. Areas on opposite sides of a fire wall are consid·

ered separate buildings b. The number of fire walls required in a structure is

generally governed by allowable height and area limits, based on occupancy and type of construction

c. All fire-wall openings must be protected by ap­proved fire-rated assemblies

3. In terms of physical characteristics, the principal differ­ences between fire walls and other wall assemblies lies in their superior fireresistance and ability to withstand the collapse of construction on either side of the wall without collapse of the wall itself.

4. Fire walls may be used structurally when designed in accordance with the appropriate provisions of the code.

References 1. Fire Protection Handbook, 16th ed., National Fire Pro­

tection Association, Boston, Mass., 1986. 2. ASTM Designation E 119-83, Standard Methods of Fire

Tests of Building Construction and Materials, Section 4, Vol. 4.07, American Society for Testing and Mate­rials, Philadelphia, Pennsylvania, 1985.

3. The BOCA National Building Code, 10th ed., Building Officials and Code Administrators International, Inc., Country Club Hills, llinois, 1987.

4. Analytical Methods of Determining Fire Endurance of Concrete and Masonry Members-Model Code Ap­proved Procedures, SR267B, Concrete and Masonry Industry Firesafety Committee, 1985.

5. Differential Movement-Cause and Effect, BIA Tech­nical Notes on Brick Construction, No. 18, Brick lnsti· tute of America, Mclean, Virginia, July 1984.

6. Control of Wall Movement with Concrete Masonry, NCMA·TEK 3, National Concrete Masonry Associa­tion, Herndon, Virginia, 1972.

7. Design of Concrete Masonry for Crack Control, NCMA­TEK 53, National Concrete Masonry Association, Herndon, Virginia, 1973.

8. Building Movement and Joints, EB086B, Portland Cement Association, Skokie, Illinois, 1982.

9. "Appendix P-Calculated Fire Resistance," Standard Building Code, Southern Building Code Congress International, Birmingham, Ala., 1985, p. 475.

Organizations represented on the Concrete and Masonry Industry Firesafety Committee BIA Brick Institute of America CRSI Concrete Reinforcing Steel Institute ESCSI Expanded Shale Clay and Slate Institute NCMA National Concrete Masonry Association NRMCA National Ready Mixed Concrete Association PCA Portland Cement Association PCI Prestressed Concrete Institute

This publication is intended for the use of professional personnel competent to evaluate the s1gn1ficance and limitations of 1ts contents and who will accept responsibility for the application of the material it contains The Concrete and Masonry Industry Firesafety Committee disclaims any and

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all responsibility for application of the stated principles or for the accuracy of the sources other than work performed or Information developed by ( the Committee.

Printed in U SA

Concrete and Masonry Industry Firesafety Committee 5420 Old Orchard Road, Skokie, Illinois 60077-1 083

SR291.01B