U. S. DEPARTMENT OF COMMERCE

NATIONAL BUREAU OF STANDARDS

AMERICAN STANDARD

BUILDING CODE REQUIREMENTS FOR MASONRY

MISCELLANEOUS PUBLICATION M174

U. S. DEPARTMENT OF COMMERCE

JESSE H. JONES, Secretary NATIONAL BUREAU OF STANDARDS

LYMAN J. BRIGGS, Director

NATIONAL BUREAU OF STANDARDS MISCELLANEOUS PUBLICATION M174

AMERICAN STANDARD BUILDING CODE

REQUIREMENTS FOR MASONRY

By

Sectional Committee on Building Code Requirements and

Good Practice Recommendations for Masonry—A41

Under the Sponsorship of the

National Bureau of Standards

Issued March 15, 1944

Approved

January 22, 1944, by the American Standards Association

as American Standard A41.1-1944

UNITED STATES

GOVERNMENT PRINTING OFFICE WASHINGTON : 1949

For sale by the Superintendent of Documents, U. S. Government Printing Office Washington 25, D. C. - Price 15 cents

FOREWORD

This standard, developed under ASA project A41, Building Code

Requirements and Good Practice Recommendations for Masonry,

presents recommended building code requirements for nonreinforced

masonry.

The standard is one of a related series presenting recommended

basic building code requirements that are being developed by technical committees under the procedure of the American Standards

Association. The general building code program is under the supervision of the Building Code Correlating Committee of the Association.

The objectives of the program and information concerning the

several technical committees and the Building Code Correlating

Committee are given in an announcement, Building Code Standardization, which may be obtained from the American Standards Association

Lyman J. Briggs, Director

m
SECTIONAL COMMITTEE

The personnel of the Sectional Committee on Building Code Requirements and Good Practice Recommendations for Masonry—A41,

which developed this standard, is as follows: National Bureau op Standards, Sponsor D. E. Parsons, Chairman

J. W. McBurney, Secretary

Organization represented Representative

American Ceramic Society J. W. Whittemore.

American Institute of Architects Theodore Irving Coe. American Public Works Association Roy L. Phillips.

American Society of Civil Engineers George L. Lucas.

J. S. Langthorn.

American Society for Testing Materials Raymond E. Davis.

T. R. Lawson.

J. W. Whittemore (Alternate). Associated General Contractors of America, Russell H. Hunter.

Inc. Bricklayers, Masons and Plasterers Interna- Thomas A. Murray.

tional Union of America. Thomas Murphy (Alternate). Building Officials' Conference of America Andrew C. H. Leak.

Lyle D. Webber (Alternate). Building Trades Employers Association of Emil Diebitsch.

the City of New York. Peter W. Eller.

Federal Works Agency, Public Buildings C. W. Chamberlain.

Administration. J. W. Strohman, (Alternate). The Finishing Lime Association of Ohio L. E. Johnson.

Fire Protection Group Clinton T. Bissell.

Mason Contractors Association of the U. S., James A. Keithly.

Inc. National Association of Real Estate Boards H.U. Nelson.

National Bureau of Standards P. H. Bates. D. E. Parsons (Alternate). National Concrete Masonry Association E. W. Dienhart.

National Crushed Stone Association, Inc A. T. Goldbeck.

National Housing Agency Walter Junge.

F. W. Milliken (Alternate). National Lime Association S. Walter Stauffer.

National Sand and Gravel Association „ Stanton Walker.

National Slag Association H. J. Love. Fred Hubbard (Alternate). New England Building Officials' Conference Alexander Addeo.

Pacific Coast Building Officials' Conference Hal Colling.

Portland Cement Association P. M. Woodworth.

H. F. Gonnerman (Alternate). Sand-Lime Brick Association Thomas H. Lineweaver (Alter- nate). Structural Clay Products Institute H. C. Plummer.

U. S. Department of Labor R. P. Blake.

Western Society of Engineers J. C. Sanderson.

Members-at-Large Henry D. Dewell.

Sullivan W. Jones. Rudolph P. Miller.

Walter C. Voss. George N. Thompson, vice chairman, and J. H. Courtney, technical secretary, , of the ASA Building Code Correlating Committee, serve as ex-officio members of

this committee in order to coordinate the requirements of A41 standards with ! others in the building code program.

IV
CONTENTS

Page

Foreword . in

Sectional Committee iv Section 1. General 1 1-1. Application of requirements 1

i 1-2. Definitions , 1 1-3. Tests 3

1-4. Second-hand materials 3

1-5. Materials and methods of construction not covered in these requirements 4 Section 2. Materials 4

2-1. Solid masonry units (clay or shale) 4

2-2. Sand-lime brick 4

2-3. Concrete brick 5

2-4. Structural clay tile 5

2-5. Concrete masonry units 5

2-6. Plain concrete 5

2-7. Cast stone . 6

2-8. Natural stone 6

2-9. Architectural terra cotta 6

2-10. Glazed building units 6

2—11. Gypsum tile and block 6

2-12. Structural glass block 6 2-13. Mortar materials 6

2-14. Mortar requirements 6

2-15. Classification of mortar 7

2-16. Types of mortars required 7 Section 3. Allowable Stresses in Masonry 8

3-1. General 8

3-2. Composite walls 8

3-3. Solid masonry units 8

3-4. Hollow masonry units 9

3-5. Plain concrete , 9

3-6. Stone and cast stone 9 Section 4. Lateral Support 9 Section 5. Solid Masonry Walls 10

5-1. Thickness of solid masonry bearing walls . 10

5-2. Thickness of solid masonry nonbearing walls 11 5-3. Bond 11 Section 6. Walls of Structural Clay Tile or Hollow Concrete

Masonry Units 11 6-1. Thickness and height 11 6-2. Bond 11 ection 7. Solid Walls of Plain Concrete 11 7-1. Thickness 11

7-2. Plain concrete 12

7-3. Reinforcement 12 Section 8. Stone Walls 12 8-1. Thickness _ 12 8-2. Bond 12 Section 9. Cavity Walls and Hollow Walls of Solid Units 12 9-1. Allowable stresses 12

9-2. Height 13

9-3. Thickness 13

9-4. Bond 13

9-5. Drainage 13 Section 10. Veneered Walls 13

10-1. Material 13

10-2. Allowable stresses 14

10-3. Height 14

10-4. Attachment of veneering 14 v
VI CONTENDS

Page Section 11. Faced Walls 14

11-1. Material 14

11-2. Allowable stresses 14

11-3. Thickness 14 11-4. Bond 14 Section 12. Foundation Walls 15 Section 13. Piers 16 Section 14. Structural Glass Block _ 16 Section 15. Parapet Walls 16 Section 16. Partitions 16

16-1. Bearing partitions 16 16-2. Nonbearmg partitions 16 Section 17. Miscellaneous Masonry Requirements 16 17—1. Bonding of wall intersections 16

17-2. Anchoring of walls 17

17-3. Chases and recesses 17

17-4. Lintels and arches 18

17-5. Separation of combustible structural members 18

17-6. Beam supports ; 18

17-7. Corbelling of chimneys 18

17-8. Cornices 18 Section 18. Existing Walls 19 Section 19. Erection 19 Appendix 19

1-3. Tests . 20

1-4. Second-hand materials 20

1-5. Materials and methods of construction not covered in these requirements 20

2. Reference to standards 21 2-1. Durability of masonry units 22

2-14. Mortar requirements 23

2-15. Classification of mortar 24

2-16. Types of mortar required 25

3. Allowable stresses in masonry 25

3-1 (b). Higher stresses 27 3-2. Composite walls 28

4. Lateral support 28

5-1. Thickness of solid masonry bearing walls 28

5-2. Thickness of solid masonry nonbearing walls : 29

5-3. Bond 30 6-1. Thickness and height of walls of structural clay tile or hollow

concrete masonry units 30

7-1. Thickness of solid walls of plain concrete 30 8-1. Thickness of stone walls 30

9. Cavity walls and hollow walls of solid units 30 9-4. Bond 32

10-4. Attachment of veneering 32

12. Foundation walls 32 12-2. Minimum thickness of foundation walls .. 33

13. Piers 34

15. Parapet walls 34

16-2. Nonbearing partitions 34

17-3. Chases and recesses 34

19-1. Winter construction . 35

19-2. Wetting of bricks (clay or shale) 35

19-3. Erection 35

Construction to resist earthquakes 36

References and notes 36
American Standard Building Code Requirements

For Masonry

By

Sectional Committee on Building Code Requirements and Good

Practice Recommendations for Masonry—A41

Under the Sponsorship of the National Bureau of Standards

ABSTRACT

Building Code Requirements for Masonry (ASA A41. 1-1944) is a complete

code of minimum requirements for masonry construction including definitions, requirements for materials, allowable stresses, and general requirements for all types of masonry except reinforced masonry. This document, prepared by

American Standards Association Sectional Committee A41 under the sponsorship

of the National Bureau of Standards, is one of a series of building code standards prepared by various committees under the jurisdiction of the Building Code

Correlating Committee of the American Standards Association. The basis of the requirements of this code is discussed in an appendix.

SECTION 1. GENERAL

1-1. Application of requirements.

(a) Masonry, as defined in this standard, when used in any building

or structure shall conform to these requirements.

(b) A material other than one of those specifically named in the

definition of masonry, which is incombustible and otherwise suffi- ciently embodies the characteristics of one of the materials named,

and which satisfies the requirements for that material, may be classed

by the building official with that material which it most closely

resembles.

1-2. Definitions.

ACI means the American Concrete Institute.

ASA means the American Standards Association.

ASTM means the American Society for Testing Materials.

FS means Federal Specification.

Approved, as applied to a material, device, or mode of construction, means approved by the building official under the provisions of the

building code, or by other authority designated by law to give approval

in the matter in question.

Architectural terra cotta is plain or ornamented (modeled or molded)

hard-burned building units, larger in size than brick, consisting of mixtures of plastic clays, fusible minerals, and grog, and having a

glazed or unglazed ceramic finish. Ashlar facing is a facing composed of solid rectangular units of burned clay or shale, or natural or cast stone, larger in size than brick,

having sawed, dressed, or squared beds, and joints laid in mortar.

1
2 Miscellaneous Publications, National Bureau of Standards

Ashlar masonry is masonry composed of rectangular units of burned

clay or shale, or natural or cast stone, larger in size than brick and

properly bonded, having sawed, dressed, or squared beds, and joints

laid in mortar.

Brick is a material of construction in small, regular units, formed

from inorganic substances and hardened in a shape approximating a rectangular prism approximately 8 by 3% by 2% inches in size, the net

cross-sectional area of which in any plane parallel to the bearing

surface is not less than 75 percent of its gross cross-sectional area measured in the same plane.

Building means a combination of materials to form a construction

that is safe and stable, and adapted to continuous occupancy for resi- dence, business, industrial, assembly, or storage purposes. The term

building shall be construed as if followed by the words "or part

thereof."

Building official means the officer or other person charged with the

administration and enforcement of the building code, or his duly

authorized representative. Concrete masonry unit is a building unit made from cement and

suitable aggregates, such as sand, gravel, crushed stone, cindefs,

burned clay or shale, or blast-furnace slag.

Height as applied to a wall means the vertical distance to the top,

including parapet, measured from the foundation wall, or from a

girder or other immediate support of the wall. Hollow masonry unit is a masonry unit whose net cross-sectional area in any plane parallel to the bearing surface is less than 75 percent

of its gross cross-sectional area measured in the same plane.

Masonry means architectural terra cotta, brick, and other solid masonry units of clay or shale, concrete masonry units, glazed building

units, gypsum tile or block, plain concrete, stone, structural clay tile, structural glass block, or other similar building units or materials, or a combination of same, bonded together with mortar.

Mortar is a plastic mixture of cementitious material, fine aggregate,

and water. Nominal dimension is a dimension that may vary from actual

masonry dimension by the thickness of a mortar joint but not to exceed

one-half inch.

Partition.

Bearing partition is an interior bearing wall one story or less in height.

Nonbearing partition is an interior nonbearing wall one story or

less in height.

Pier means an isolated column of masonry; a bearing wall not

bonded at the sides into associated masonry shall be considered a

pier when its horizontal dimension measured at right angles to the

thickness does not exceed four times its thickness.

Required means required by some provision of these requirements.

Rubble.

Coursed rubble is masonry composed of roughly shaped stones

fitting approximately on level beds and well bonded.

Random rubble is masonry composed of roughly shaped stones

laid without regularity of coursing, but well bonded and fitted together to form well-defined joints.

\
Building Code Requirements for Masonry 3

Bough or ordinary rubble is masonry composed of unsquared or

' field stones laid without regularity of coursing but well bonded.

Solid masonry is masonry consisting of solid masonry units laid

| contiguously with the joints between the units filled with mortar, or

i consisting of plain concrete. Solid masonry unit is a masonry unit whose net cross-sectional area

; in every plane parallel to the bearing surface is 75 percent or more of

i its gross cross-sectional area measured in the same plane. Net cross- sectional area shall be taken as the gross cross-sectional area minus

i the area of the cores or cellular space. Gross cross-sectional area

. shall be determined to the outside of the scoring, but the cross-seci tional area of the grooves shall not be considered as part of the area

; of the coring and shall not be deducted from the gross cross-sectional area to obtain the net cross-sectional area,

i Story is that portion of a building included between the upper sur- face of any floor and the upper surface of the floor next above, except

that the top story shall be that portion of a building included between

| the upper surface of the nighest finished floor and the ceiling or roof

above.

Structural clay tile is a hollow masonry unit composed of burned clay,

shale, fire clay, or mixtures thereof and having parallel cells.

I Walls.

Bearing wall is a wall which supports any vertical load in addition

I to its own weight.

i Cavity wall is a wall built of masonry units or of plain concrete, or a combination of these materials, so arranged as to provide an

I air space within the wall, and in which the facing and backing of

! the wall are tied together with metal ties.

, Faced wall is a wall in which the masonry facing and backing are

so bonded as to exert common action under load.

Foundation wall is a wall below the floor nearest grade serving as

, a support for a wall, pier, column, or other structural part of a

building.

j Hollow wall of masonry is a wall built of masonry units so arranged

' as to provide an air space within the wall, and in which the facing

and backing of the wall are bonded together with masonry units.

Nonbearing wall is a wall which supports no vertical load other

[ than its own weight.

Parapet wall is that part of any wall entirely above the roof line. Party wall is a wall used or adapted for joint service between two

buildings.

, Veneered wall is a wall having a masonry facing which is attached

f to the backing but not so bonded as to exert common action under load

1-3. Tests.—The building official may require reasonable tests of masonry materials from time to time to determine their quality and

whether they conform to these requirements. Such tests shall be

made in accordance with the standards prescribed for the material

in question. In the absence of such standards, the building official shall specify the method and manner of making the tests.

; 1-4. Second-Hand Materials.—Second-hand materials shall not be

[ used in masonry, unless such materials conform to these requirements

and have been thoroughly cleaned.

833794 O - 49 - 2
4 Miscellaneous Publications, National Bureau of Standards

1-5. Materials and Methods of Construction Not Covered in These

Requirements.

(a) The use of masonry materials or methods of construction not

covered by these requirements may be permitted, provided that the

materials conform to specifications insuring reasonable uniformity of the product; and that the stability and durability of the construction,

and its resistance under fire exposure shall have been demonstrated

to the satisfaction of the building official. (b) Where tests are required by the building official the test assembly shall be truly representative of the construction for which

approval is desired as to materials, workmanship, and details, and

shall be built under conditions representative of those in building

construction.

(c) Test panels to determine the strength of wall construction shall be from 4 to 6 feet in width and from 8 to 9 feet in height. Tests shall be made 28 days after fabrication of the test panel.

(d) In compressive tests the panel shall be tested as a column having

a flat end at the bottom. The resultant of the load shall be applied

uniformly along a line at the top parallel to the inside face, and onethird the thickness of the panel from the inside face exclusive of the

wall finish. In transverse tests two equal loads shall be applied,

each at one-quarter of the span from the supports.

(e) Allowable stresses in compression shall be fixed at not more

than one-sixth of the average compressive strength of the test as- semblies, as determined by responsible authorities.

SECTION 2. MATERIALS

2-1. Solid Masonry Units (Clay or Shale).

(a) Brick subject to the action of weather or soil, but not subject

to frost action when permeated with water, shall conform to the

requirements for grade MW brick of the Tentative Specifications for Building Brick (Made from Clay or Shale), ASTM C 62-41 T. When

not subject to the action of weather or soil, brick shall conform to the

requirements for grade NW brick. Note.—Grade SW of the above specification should be required where

brick may be subject to temperature below freezing while permeated with

water. In localities where brick conforming in physical properties to the requirements of this specification is not readily obtainable, the use of other brick should be permitted if suitable evidence of resistance to weathering is presented to the building official. (b) Other solid masonry units of clay or shale shall meet the re- quirements for physical properties of brick as specified in Section

2-1 (a). 2-2. Sand-Lime Brick.—Sand-lime brick subject to the action of weather or soil, but not subject to frost action when permeated with

water, shall conform to the requirements for grade MW brick of the

American Standard Specifications for Sand-Lime Building Brick, ASA 1 A78. 1-1942 (ASTM C 73-39). When not subject to the action of

> Where reference is made to standards by abbreviation of the title of the sponsor organization, the abbreviation shall have the following meaning: ASA means American Standards Association, ASTM -means American Society for Testing Materials, ACI means American Concrete Institute, and FS means Federal

Specification.
Building Code Requirements for Masonry 5

weather or soil, sand-lime brick shall conform to the requirements for grade NW brick. Note.—Grade SW of the above specification should be required where

brick may be subject to temperature below freezing while permeated

l with water. 2-3. Concrete brick.—Concrete brick subject to the action of weather

lor soil shall conform to the requirements for grade A brick of the

American Standard Specifications for Concrete Building Brick, ASA

A75. 1-1942 (ASTM C 55-37>. When not subject to the action of

i weather or soil, concrete brick shall conform to the requirements for

I grade B brick.

2-4. Structural Clay Tile.

(a) Structural clay tile subject to the action of weather or soil shall

I conform to the requirements for grade LBX tile of the American

Standard Specifications for Structural Clay Load-Bearing Wall Tile,

ASA A74.1-1942 (ASTM C 34-41).

i (b) Structural clay tile used in load-bearing masonry but not subI ject to the action of weather or soil shall- conform to the requirements

for grade LB tile of the above specification.

(c) Structural clay tile used in interior non-load-bearing masonry

, shall conform to the requirements of the American Standard Specifications for Structural Clay Non-Load-Bearing Tile, ASA A76. 1-1942

; (ASTM C 56-41).

2-5. Concrete Masonry Units.

(a) Hollow concrete masonry units used in load-bearing masonry

or subject to the action of weather or soil shall conform to the requirements of the American Standard Specifications for Hollow LoadBearing Concrete Masonry Units, ASA A79.1-1942 (ASTM C 90-39).

(b) Hollow concrete masonry units used in non-load-bearing masonry

not subject to the action of weather or soil shall conform to the re- quirements of the American Standard Specifications for Hollow NonLoad-Bearing Concrete Masonry Units, ASA A80. 1-1942 (ASTM

C 129-39).

(c) Solid concrete masonry units shall conform to the requirements

of the American Standard Specifications for Solid Load-Bearing Concrete Masonry Units, ASA A81. 1-1942 (ASTM C 145-40).

2-6. Plain Concrete.

(a) Cast-in-place concrete construction, reinforced only for shrinkage or temperature changes shall be classed as plain concrete. Plain

concrete other than concrete fill shall have a minimum compressive

strength at 28 days of 2,000 psi.

(b) Portland cement shall conform to the requirements of the

Standard Specifications for Portland Cement, ASTM C 150-42.

(c) Natural Gement shall conform to the requirements of the

Standard Specifications for Natural Cement, ASTM C 10-37.

(d) Concrete aggregates shall conform to the requirements of the

Standard Specifications for Concrete Aggregates, ASTM C 33-42.

The maximum size of the aggregates shall not exceed one-fifth of the

narrowest dimension between forms of the member for which the

concrete is to be used, nor 2% inches.

(e) Water used in mixing concrete shall be clean, and free from

deleterious amounts of acids, alkalis, or organic materials. Note.—Water suitable for drinking purposes is satisfactory.
6 Miscellaneous Publications, National Bureau of Standards

2-7. Cast Stone.—Cast s^one shall conform to the requirements of the Specification for Cast Stone, ACI 704-44.

2-8. Natural Stone.—Stone for masonry shall be sound and free from

loose or friable inclusions. It shall have sufficient strength, durability,

and resistance to impact for the proposed use

2-9. Architectural Terra Cotta.—Architectural terra cotta shall have a strong homogeneous body and give a sharp metallic, bell-like ring

when struck. All units shall have the necessary anchor holes and

shall be so formed as to engage properly with the supporting structure. 2-10. Glazed Building Units.—Glazed building units shall conform to the requirements of the Tentative Specifications for Glazed Building

Units ASTM C 126-39 T except that the requirements for finish shall not apply to salt-glazed building units.

2-11. Gypsum Tile and Block.

(a) Gypsum partition tile or block shall conform to the requirements of the Standard Specifications for Gypsum Partition Tile or Block, ASTM C 52-41.

(b) Gypsum partition tile or block shll not be used in bearing walls or

in exterior walls, or where subject to continous dampness.

2-12. Structural Glass Block.—Glass blocks may be solid or hollow.

All mortar bearing surfaces of the blocks- shall be precoated with a

material to improve adhesion between mortar and glass.

2-13. Mortar Materials.

(a) Cementitious materials used in mortars shall conform to the

requirements of the following applicable standard specifications:

Quicklime for Structural Purposes, ASTM C 5-26.

Hydrated Lime for Structural Purposes, ASTM C 6-31.

Hydraulic Hydrated Lime for Structural Purposes, ASTM C 141^12.

Natural Cement, ASTM C 10-37.

Masonry Cement, Federal Specification SS-C-181b.

Portland Cement, ASTM C 150-42.

(b) Aggregate for mortar shall conform to the requirements of the

Tentative Specifications for Aggregate for Masonry Mortar, ASTM C

144-42 T.

Note.—Materials which have been found in practice to cause harmful

volume changes should not be incorporated in masonry.

(c) Water used in mixing mortar shall be clean, and free from

deleterious amounts of acids, alkalis, or organic materials.

Note.—Water suitable for drinking purposes is satisfactory.

2-14. Mortar Requirements.

(a) Mortar as delivered to the mason shall have a flow after suction

for 1 minute of not less than 65 percent of that immediately before

suction. The flow shall be determined by the method of the Water

Retention Test of the Federal Specification for Masonry Cement,

SS-C-181b.

(b) The volume of aggregate in mortar shall be at least two times,

but not more than three times the volume of cementitious material.
Building Code Requirements for Masonry 7

2-15. Classification of Mortar.

(a) Mortar used in masonry construction shall be classified as

follows:

Type

Minimum compressive strength of 2- inch cubes at 28 days A

psi 2,500 600 200

75 B

C __ D

(b) Unless the strength classification of the mortar has been otherwise established by test as prescribed in Section 2-15 (c), mortars of

the following proportions, with the aggregate measured in a damp

and loose condition, may be assumed to meet the strength classifica- tion given in Section 2-15 (a). Proportions by volume

Mortar

type Cement

Hydrated lime

or lime putty

allowable range Aggregate measured in a damp and

loose condition A

B

B

1 (portland)

1 (portland)

1 (masonry FS type II)

to %

1 to 1^

Not more than 3. Not more than 6. Not more than 3. Not more than 9. Not more than 3. Not more than 3 parts for each part of cementitious

material.

C

C

D _

1 (portland) _ _ 1 (masonry FS type I) to Y% (portland) __

2 to 2/2

1 to 1%

Note.—The weights per cubic foot of the materials in mortar are considered to be as follows:

Weight per cubic foot Portland cement 94 lb. Masonry cement Weight printed on bag.

Hydrated lime 40 lb. Sand, damp and loose 1 cu ft contains 80 lb of dry sand.

(c) Mortar of materials conforming to the requirements of Section 2-13, and of any proportions conforming to Section 2-14 (b),

may qualify as mortar of any one of the four types, provided it con- forms to the physical requirements of Sections 2-14 (a) and 2-15 (a). When it is desired to establish the strength classification of a given

mortar by test, the strength . shall be determined with mortar pre- pared in a testing laboratory, of representative materials and in the

proportions proposed for use. The test cubes shall be molded, cured,

and tested for compressive strength as described in the Federal

Specification for Masonry Cement, SS-C-181b, except that for type D

mortar the entire curing shall be in laboratory air at 70° F±5°.

2-16. Types of Mortars Required.—Masonry shall be laid in type A,

type B, or type C mortar, except as follows:

(a) Type A mortar shall be used in nominal 10-inch cavity walls,

foundation walls of hollow masonry units, and masonry linings of

existing masonry walls.
8 Miscellaneous Publications, National Bureau of Standards

(b) Type A or type B mortar shall be used in footings, foundation

walls of solid masonry units, isolated piers, load-bearing or exterior

walls of hollow masonry units, hollow walls of masonry, and cavity

walls exceeding nominal 10-inch thickness.

(c) Type D mortar may be used in solid masonry walls,, other than

parapet walls or rubble stone walls, not in contact with the soil and

not less than 12 inches thick nor more than 35 feet in height, provided

the walls are laterally supported at intervals not exceeding 12 times

the wall thickness.

(d) Gypsum partition tile and block shall be laid in gypsum

mortar. Nonbearing partitions and fireproofing of structural clay

tile may be laid in gypsum mortar. Fire brick shall be laid in fire clay or air-setting mortar.

(e) Glass block when laid in mortar shall be laid in type B mortar. SECTION 3. ALLOWABLE STRESSES IN MASONRY

3-1. General.

(a) Every building or structure hereafter erected and all new construction in the alteration of an existing building or structure shall be so designed and constructed that the working stresses prescribed

in this section are not exceeded. In using these stresses, the effects of all loads and conditions of loading and the influence of all forces

affecting the design and strength of the several parts shall be taken

into account.

(b) Higher stresses than herein specified may be used, but only if it is clearly established to the satisfaction of the building official, by

test or other satisfactory evidence, that material of a higher grade or a superior workmanship than is generally provided in accepted good

practice is to be employed under approved inspection. The use of

higher stresses, however, shall not be allowed until a statement, giving

the reasons for such permission, together with the facts and circumstances on which it is based, is placed on file and made a part of the

official record of the permit.

3-2. Composite Walls.—In walls or other structural members composed of different kinds or grades of units or mortar, the maximum

stress shall not exceed the allowable stress for the weakest of the combinations of units and mortars of which the member is composed.

3-3. Solid Masonry Units.—The allowable compressive stresses in pounds per square inch of gross cross-sectional area in solid masonry

of solid units shall not exceed the following limits: Brick and other solid units of clay or shale; sand-lime or concrete brick

Average compressive strength of units tested in the position taken

in the masonry

Mortar type A B C D

psi psi psi psi psi 8,000 plus 400 300 200 100

4,500 to 8,000 250 200 150 100

2,500 to 4,500 175 140 110 75

1,500 to 2,500 125 100 75 50

Note.—For allowable stresses in hollow walls of solid units and in cavity walls, see Section 9, Cavity Walls and Hollow Walls of Solid Units.
Bwilding Code Requirements for Masonry 9

Solid concrete-masonry units

Grade Mortar type. A B C

psi psi pat Grade A 175 125 80 Grade B 125 100 60

3-4. Hollow Masonry Units.—The allowable compressive stresses in pounds per square inch of gross cross-sectional area in masonry of hollow units of structural clay tile or of hollow concrete masonry

units shall not exceed the following limits:

Unit Mortar type A B

Hollow units

pst 85

psi 70

3-5. Plain Concrete.—The allowable stresses shall not exceed 25 per- cent for compression, and 3 percent for tension in extreme fibre in

flexure, of the compressive strength of the concrete. When the ratio

of height to thickness of structural members of plain concrete exceeds

10, the above percentage for compression shall be reduced proportionately to 18 percent for a ratio of height to thickness of 20. 3-6. Stone and Cast Stone.—The allowable stresses in compression,

in pounds per square inch of gross cross-sectional area shall not exceed

the following limits:

Material Mortar

Granite, ashlar.__

Limestone, ashlar Marble, ashlar Sandstone, ashlar Cast stone Rubble stone

pst 800

500

500 400

400

140

pst 640 400

400

320

320

100

pst 500

325 325 250

250

80

pst 400 250

250

160

160

SECTION 4. LATERAL SUPPORT

4-1. Solid masonry walls shall be supported at right angles to the

wall face at intervals not exceeding 20 times the nominal wall thickness

if laid in type A, B, or C mortar, and not exceeding 12 times the

nominal wall thickness if laid in type D mortar.

4-2. Walls of structural clay tile or hollow concrete masonry units,

and hollow walls of masonry shall be supported at right angles to the

wall face at intervals not exceeding 18 times the nominal wall thickness.

4-3. Cavity walls shall be supported at right angles to the wall face

at intervals not exceeding 14 times the nominal wall thickness.
10 Miscellaneous Publications, National Bureau of Standards

4-4. Lateral support may be obtained by cross walls, piers, or buttresses, when the limiting distance is measured horizontally, or by

floors and roofs when the limiting distance is measured vertically.

Sufficient bonding or anchorage shall be provided between the walls

and the supports to resist the assumed wind force, acting either inward

or outward. Piers or buttresses relied upon for lateral support shall have sufficient strength and stability to transfer the wind force, acting

in either direction, to the ground. When walls are dependent upon

floors or roofs for their lateral support, provision shall be made in the

building to transfer the lateral forces to the ground.

4-5. Except for window-paneled backs, and permissible chases and

recesses, walls shall not vary in thickness between their lateral supports. When a change in thickness, due to minimum thickness

requirements, occurs between floor levels, the greater thickness shall be carried up to the higher floor level. SECTION 5. SOLID MASONRY WALLS

5-1. Thickness of Solid Masonry Bearing Walls.

(a) The thickness of solid masonry bearing walls shall be sufficient at all points to keep the combined stresses due to live,. dead, and other

loads for which the building is designed within the limits prescribed

by Section 3, Allowable Stresses in Masonry.

(b) Except as otherwise provided in this section, the minimum

nominal thickness of solid masonry bearing walls shall be 12 inches

for the uppermost 35 feet of their height, and shall be increased 4

inches for each successive 35 feet or fraction thereof, measured

downward from the top of the wall.

(c) Where solid masonry bearing walls are stiffened at distances

not greater than 12 feet apart by cross walls, or by internal or external

offsets or returns at least 2 feet deep, or by reinforced concrete floors,

they may be of 12-inch nominal thickness for the uppermost 70 feet,

measured downward from the top of the wall, and shall be increased

4 inches in thickness for each successive 70 feet or fraction thereof.

(d) In buildings not more than three stories in height, solid masonry

bearing walls of the top story may be of 8-inch nominal thickness

when the total height of the wall does not exceed 35 feet, provided

that such 8-inch walls do not exceed 12 feet in height and that the

roof beams are horizontal.

(e) In residential buildings not more than three stories in height,

solid masonry bearing walls may be of 8-inch nominal thickness

when not over 35 feet in height. Such walls in one-story singlefamily dwellings, and 1-story private garages, may be of 6-inch nominal thickness when not over 9 feet in height, provided that when gable

construction is used an additional 6 feet is permitted to the peak of

the gable.

(f) Solid masonry walls above roof level, 12 feet or less in height,

enclosing stairways, elevator shafts, penthouses, or bulkheads may

be of 8-inch nominal thickness and may be considered as neither

increasing the height nor requiring any increase in the thickness of the

wall below, provided the requirements for allowable stresses are met.

Note.—For requirements for lateral support, see Section 4, Lateral

Support,; for hollow walls, see Section 9, Cavity Walls and Hollow Walls

of Solid Units; for veneered walls, see Section 10, Veneered Walls; for faced walls, see Section 11, Faced Walls.
Bmlding Code Requirements for Masonry 11

5-2. Thickness of Solid Masonry Nonbearing Walls.—Nonbearing

walls of solid masonry may be 4 inches less in thickness than required

for bearing walls, but the nominal thickness shall be not less than 8

inches except where 6-inch walls are specifically permitted.

Note.—For requirements for lateral support, see Section 4, Lateral Support.

5-3. Bond.—The facing and backing of solid masonry walls shall be

bonded either with at least one full header course in each seven

courses, or with at least one full-length header in each 1.5 square

feet of wall surface. The distance between adjacent full-length

headers shall not exceed 20 inches either vertically or horizontally.

In solid brick walls of more than 8-inch nominal thickness, the inner

joints of header courses shall be covered with another header course which shall break joints with the course below.

SECTION 6. WALLS OF STRUCTURAL CLAY TILE OR HOLLOW

CONCRETE MASONRY UNITS

6-1. Thickness and Height.

(a) The thickness of walls of structural clay tile or hollow concrete masonry units shall be sufficient at all points to keep the combined

stresses due to live, dead, and other loads for which the building is designed within the limits prescribed by Section 3, Allowable Stresses

in Masonry.

(b) The minimum thickness of walls of structural clay tile or hollow

concrete masonry units shall be not less than that required for solid masonry walls under Section 5, Solid Masonry Walls.

(c) Walls of structural clay tile or hollow concrete masonry units

shall not exceed 50 feet in height above the support of such walls. Note.—For requirements for lateral support, see Section 4, Lateral Support.

6-2. Bond.

(a) Hollow masonry units shall have full mortar coverage of the

face shells in both the horizontal and vertical joints.

(b) Where two or more hollow units are used to make up the thick- ness of a wall, the stretcher courses shall be bonded at vertical in- tervals not exceeding 34 inches by lapping at least 3% inches over the

unit below, or by lapping with units at least 50 percent greater in thickness than the units below at vertical intervals not exceeding 17

inches.

(c) Where walls of hollow masonry units are decreased in thickness, a course of solid masonry shall be interposed between the wall below

and the thinner wall above.

SECTION 7. SOLID WALLS OF PLAIN CONCRETE

7-1. Thickness.

(a) The thickness of walls of plain concrete shall be sufficient at

all points to keep the combined stresses due to live, dead, and other

loads for which the building is designed within the limits prescribed

by Section 3, Allowable Stresses in Masonry.

(b) The minimum thickness of walls of plain concrete may be 2

irches less than that required for solid masonry walls in Section 5,

833794 O - 49 - 3
12 Miscellaneous Publications, National Bureau of Standards

Solid Masonry Walls, but not less than 8 inches, except that 6-inch

walls of plain concrete may be permitted where 6-inch walls are

specifically permitted by Section 5-1 (e). Note.—For requirements for lateral support, see Section 4, Lateral Suport; for hollow walls, see Section 9, Cavity Walls and Hollow Walls

of Solid Units; for veneered walls, see Section 10, Veneered walls; for faced walls, see Section 11, Faced Walls. 7-2, Plain Concrete.—Except as otherwise specifically provided in these requirements, the Building Regulations for Reinforced Concrete, ACI 318-41 shall be deemed to be the generally accepted good

practice in plain concrete construction.

7-3. Reinforcement.—Reinforcement symmetrically disposed in the

thickness of the wall shall be placed not less than 1 inch above and

2 inches below openings and extond not less than 24 inches each side of such openings or be of equivalent length with hooks. The reinforcement both above and below shall consist of one /g-inch round rod for each 6 inches in wall thickness or fraction thereof. SECTION 8. STONE WALLS

8-1. Thickness.

(a) The thickness of stone walls shall be sufficient at all points to keep tlie combined stresses due to live, dead, and other loads for which the building is designed within the limits prescribed by Section 3, Allowable Stresses in Masonry.

(b) The minimum thickness of walls of stone ashlar shall be not less than that required for solid masonry walls under Section 5, Solid

Masonry Walls.

(c) Rubble stone walls shall be 4 inches thicker than is required for

solid masonry walls of the same respective heights, but in no case

less than 16 inches thick. Note.—For requirements for lateral support, see Section 4, Lateral Support.

8-2. Bond.

(a) In ashlar masonry, bond stones uniformly distributed shall be

provided to the extent of not less than 10 percent of the area.

(b) Rubble stone masonry 24 inches or less in thickness shall have

bond stones with a maximum spacing of 3 feet vertically and horizontally, and if the masonry is of greater thickness than 24 inches,

shall have one bond stone for each 6 square feet of wall surface on

both sides. SECTION 9. CAVITY WALLS AND HOLLOW WALLS OF SOLID

UNITS

9-1. Allowable Stresses.—In cavity walls and in hollow walls of solid masonry units, the compressive stresses in psi of gross cross-sectional area shall not exceed the following:

psi Solid masonry units with mortar A 125

Solid masonry units with mortar B 100 Hollow masonry units with mortar A . 60 Hollow masonry units with mortar B 50

Plain concrete i 300 Note. —See Section 3-2 for composite walls and Section 2-16 for types of mortar permitted in cavity walls.
Building Code Requirements for Masonry 13

g-2. Height.—Except as otherwise limited by Section 9-3 (a), cavity

walls and hollow walls of solid masonry units shall not exceed 35 feet

in height.

9-3. Thickness.

(a) Cavity walls and hollow walls of solid masonry units shall be

not less in thickness than required for solid masonry walls in Section 5, Solid Masonry Walls, provided that 10-inch cavity walls shall not

exceed 25 feet in height.

(b) In cavity walls neither the facing nor backing shall be less than

3% inches in nominal thickness, and the cavity shall be not less than

2 inches nor more than 3 inches in width.

Note.—For requirements for lateral support, see Section 4, Lateral Support.

9-4. Bond.

(a) In hollow walls of solid masonry units, the facing and backing

shall be securely tied together with headers or bonding units, as required for solid masonry walls in Section 5-3 so that the parts of the wall will exert common action under the load.

(b) Where such walls are decreased in thickness, a course of solid

masonry shall be interposed between the wall below and the thinner

wall above.

(c) In cavity walls the facing and backing shall be securely tied

together with suitable bonding ties of adequate strength. A steel rod /i e inch in diameter or a metal tie of equivalent stiffness coated

with a noncorroding metal or other approved protective coating shall be used for each 3 square feet of wall surface. Where hollow masonry

units are laid with the cells vertical, rectangular ties shall be used;

in other walls the ends of ties shall be bent to 90-degree angles to provide hooks not less than 2 inches long. Ties shall be embedded in horizontal joints of the facing and backing. Additional bonding ties shall be provided at all openings, spaced not more than 3 feet apart

around the perimeter and within 12 inches of the opening. Cavity

walls of plain concrete shall be reinforced as provided in Section 7, Solid Walls of Plain Concrete.

9-5. Drainage.—In cavity walls the cavity shall be kept clear of

mortar droppings during construction. Approved flashing shall be

installed and adequate drainage provided to keep dampness away

from the backing.

SECTION 10. VENEERED WALLS

10-1. Material.

(a) Materials used for veneering shall be of the following thicknesses:

Material Thickness

Stone _ Inches Not less than 3. Not less than 3. Not less than 1%. Not less than 2%. Not less than

Not less than 1%. Not more than 1. As approved by building

official.

Cellular architectural terra cotta _ __ Architectural terra cotta slabs Brick (clay, concrete or sand-lime) Cast stone _ _ Structural clay tile Flat tile Other approved masonry
14 Miscellaneous Publications, National Bureau of Standards

(b) In stone ashlar, each stone shall have a reasonably uniform

thickness, but all stones need not necessarily be of the same thickness.

10-2. Allowable Stresses.—The maximum allowable compressive

stresses on the backing of veneered walls shall not exceed those pre- scribed in Section 3, Allowable Stresses in Masonry, for masonry

of the type wiiich forms such backing. In no case shall the veneering

be considered a part of the wall in computing the strength of bearing

walls, nor shall it be considered a part of the required thickness of bearing walls. 10-3. Height.—Veneer shall Dot exceed 35 feet in height above

foundations or other approved support.

10-4. Attachment of Veneering.

(a) The veneering shall be tied into the masonry backing either by a header for every 300 square inches of wall surface or by substantial,

noncorrodible metal wall ties spaced not father apart than 16 inches

vertically and 24 inches horizontally. Headers shall project at least 3% inches into the backing. When veneering is used, special care

shall be taken to fill all joints flush with mortar around openings.

(b) Masonry veneer on frame structures shall be securely attached

to the structure at intervals of not more than 16 inches vertically and

24 inches horizontally, with noncorrodible nails or ties. SECTION 11. FACED WALLS

11-1. Material.—Materials used in the backing and facing of faced

walls shall conform in all respects to the requirements prescribed for such materials in Section 2, Materials. Materials used for facing

shall be not less than 2% inches thick, and in no case less in thickness

than one-eighth the height of the unit.

11-2. Allowable Stresses.—The compressive stresses in faced walls

shall not exceed those permitted for composite walls in Section 3-2.

Where bonded to the backing as prescribed in Section J 1-4, the full cross section of both the facing and the backing may be considered in

computing the stresses. 11-3. Thickness.—Faced walls shall be not less in thickness than is required for masonry walls of either of the t}r pes forming the facing

and the backing. Where bonded to the backing as provided in Section 11-4, the facing may be considered a part of the wall thickness. Note.—For requirements for lateral support, see Section 4, Lateral Support.

11-4. Bond.

(a) Brick facing shall be bonded to the backing, as prescribed in Section 5-3 for solid masonry walls.

(b) Ashlar facing of either natural or cast stone shall have at least 20 percent of the superficial area extending not less than 3% inches

into the backing to form bond stones, which shall be uniformly dis- tributed throughout the wall.

(c) Every projecting stone, and, except when alternate courses are

full bond courses, every stone not a bond stone shall be securely an- chored to the backing with substantial noncorrodible metal anchors

with a cross section of not less than 0.2 square inch. There shall be

at least one anchor to each stone and not less than two anchors for each stone more than 2 feet in length and 3 square feet in superficial
Building Code Requirements for Masonry 15

area. Facing stones not over 12 square feet in area shall have at least one anchor to each 4 square feet of superficial face area.

(d) When walls of structural clay tile or hollow concrete masonry

units are faced with hollow units, the facing units shall be bonded to the backing as required by Section 6, Walls of Structural Clay Tile or Hollow Concrete Masonry Units.

SECTION 12. FOUNDATION WALLS

12-1. Foundation walls shall be of sufficient strength and thickness

to resist lateral pressures from adjacent earth and to support their

vertical loads without exceeding the stresses specified in Section 3, Allowable Stresses in Masonry; provided, that in no case shall their

thickness be less than the walls immediately above them, except as provided in Section 12-3. 12-2. Foundation walls shall be of not less than 12-inch nominal

minimum thickness, except as follows:

(a) Solid masonry walls reinforced with at least one %-inch round

deformed bar, continuous from footing to top of foundation wall, for each 2 feet of length of the wall, may be of 8-inch nominal thickness.

(b) Solid foundation walls of solid masonry units or of coursed

stone that do not extend more than 5 feet below the adjacent finished

ground level, and hollow walls of masonry and walls of hollow units

that do not extend more than 4 feet below the adjacent finished ground

level, may be 8 inches in nominal minimum thickness. These depths

may be increased to a maximum of 7 feet with the approval of the

building official when he is satisfied that soil conditions warrant such

increase. The total height of the foundation wall and the wall supported shall not exceed' that permitted by these requirements for 8-inch

walls.

(c) Foundation walls of rubble stone shall be at least 16 inches

thick. Rough or random rubble without bonding or level beds shall not be used as foundations for walls exceeding 35 feet in height, nor

shall coursed bonded rubble walls be used as foundations for wajls

exceeding 50 feet in height.

(d) Foundation walls of cast-in-place concrete shall be at least- 8

inches thick; provided that when supporting one-story structures, and

the area within the foundation walls is not excavated, they may be 6 inches thick if the total height of the foundation wall and the wall

supported is within the allowable height of 6-inch walls. 12-3. Foundation walls of 8-inch nominal thickness and conforming

to the provisions of this section ma}^ be used as foundations for singlefamily dwellings with walls of brick veneer on frame walls, or with

nominal 10-inch cavity walls, provided that the dwelling is not more

than 1% stories in height and the total height of the wall, including the

gable, is not more than 20 feet. Foundation walls of 8-inch nominal

thickness supporting brick veneer or cavity walls shall be corbelled

with solid units to provide a bearing the full thickness of the wall

above. The total projection shall not exceed 2 inches with individual

corbels projecting not more than one-third the height of the unit.

The top corbel course shall be not higher than the bottom of floor

joists and shall be a full header course. 12-4. Foundation walls shall extend below the level of frost action.
16 Miscellaneous Publications, National Bureau of Standards

SECTION 13. PIERS

The unsupported height of piers shall not exceed 10 times their

least dimension. When structural clay tile or hollow concrete masonry

units are used for isolated piers to support beams and girders, the

cellular spaces shall be filled solidly with concrete or type A mortar,

and when so constructed the allowable stresses may be increased 25

percent, provided that unfilled hollow piers may be used if their un- supported height is not more than four times their least dimension.

SECTION 14. STRUCTURAL GLASS BLOCK

Glass blocks may be used in exterior or interior nonbearing walls, or where windows are permitted. AH glass-block construction shall be nonload-bearing. Glass blocks shall be laid in mortar or in ap- proved metal frames and shall be installed in accordance with generally accepted good practice. Note.—In the absence of recognized standards of national technical

organizations, the specifications issued by manufacturers of glass blocks

shall be deemed to be the generally accepted good practice in glass-block

installation. SECTION 15. PARAPET WALLS

Parapet walls shall be at least 8 inches in nominal thickness. They

shall be not higher than four times their thickness unless laterally

supported; provided that when reinforced both horizontally and

vertically with not less than %-inch rods spaced not more than 2 feet on centers, the height shall be not more than six times the thickness.

All parapet walls shall have a coping of incombustible material.

SECTION 16. PARTITIONS

16-1. Bearing Partitions.—Bearing partitions shall be of sufficient thickness to support their vertical loads without exceeding the stresses specified in Section 3, Allowable Stresses in Masonry, but not less in

tlficknoss than required for walls by Section 4, Lateral Support.

16-2. Nonbearing Partitions.—Nonbearing partitions of masonry

shall be built solidly against floor and ceiling construction below and

above, and shall not exceed the following unsupported heights:

Thickness exclusive

of plaster Maximum

unsupported height

Inches Feit 23 12 4 15

6 20

8 25

Not over (i feet in length. SECTION 17. MISCELLANEOUS MASONRY REQUIREMENTS

17-1. Bonding of Wall Intersections.

(a) Masonry walls shall be securely anchored or bonded at points

where they intersect and where they abut or adjoin the frame of a skeleton frame building.
Building Code Requirements for Masonry 17

(b) When two bearing walls meet or intersect and the courses are

built up together, the intersections shall be bonded by laying in a

true bond at least 50 percent of the units at the intersection.

(c) When the courses of meeting or intersecting bearing walls are

carried up separately, the perpendicular joint shall be regularly toothed

or blocked with 8-inch maximum offsets and the joints provided with

metal anchors having a minimum section of % inch by 1 % inches with

ends bent up at least 2 inches, or with crosspins to form anchorage.

Such anchors shall be at least 2 feet long and the maximum spacing

shall be 4 feet. (d) Meeting or intersecting nonbearing walls shall be bonded -or anchored to each other in an approved manner.

17-2. Anchoring of Walls.

(a) Masonry walls shall be securely anchored to each tier of wood

joists or wood beams bearing on them at maximum intervals of 6

feet in one- and two-family dwellings, and 4 feet in other buildings,

by metal anchors having a minimum cross-section of % inch by 1%

inches, and at least 16 inches long, securely fastened to the joists or beams and provided with split and upset ends or other approved means for building into masonry. Girders shall be similarly anchored

at their bearings. Anchors shall be attached in a manner to be self- releasing.

(b) Masonry walls parallel to wood joists or wood beams shall be

provided with similar anchors at maximum intervals of 8 feet in one- and two-family dwellings, and 6 feet in other buildings, engaging three

joints or beams. Upset and T-ends on anchors shall develop the full strength of the anchor strap.

(c) Cast-in-place concrete slabs bearing on masonry walls shall be

considered as sufficient anchorage for the supporting walls. 17-3. Chases and Recesses.

(a) There shall be no chases in walls of less than 12-inch nominal

thickness or within the required area of any pier, and no chase in any

wall shall be deeper than one-third the wall thickness, except that in dwellings not over two stories in height vertical chases may be built in

8-inch walls under the following limitations:

In 8-inch bearing walls the chases shall not exceed 4 inches in depth,

30 inches in width, and 2 feet in height and shall not extend below the

level of joist bearing, provided that where such chases occur below

window sills the width may be not in excess of the width of the window

opening above. In any case, not less than 4 inches of masonry shall remain between the back of chase and exterior surface of wall, and the

backs and sides of all such chases in exterior walls shall be water- proofed and insulated. Masonry directly over chases wider than

12 inches shall be supported on lintels. Chases permitted in 8-inch

walls shall not be cut but shall be built in as construction progresses.

(b) No horizontal chase shall exceed 4 feet in length, nor shall the

horizontal projection of any diagonal chase exceed 4 feet in length.

There shall be at least 7% inches of masonry between chases and the

jambs of openings.

(c) Recesses for stairways or elevators may be left in walls, but in no case shall the walls at such points be reduced to less than 12 inches

unless reinforced by additional piers, or by columns or girders of steel, reinforced masonry, or concrete, securely anchored to the walls on each

side of such recesses. Recesses for alcoves and similar purposes shaT
18 Miscellaneous Publications, National Bureau of Standards

have not less than 8 inches of material at the back. Such recesses

shall be not more than 8 feet in width, and shall be arched over or spanned with lintels. (d) The aggregate area of recesses and chases in any wall shall not

exceed one-quarter the whole area of the face of the wall in any story.

(e) Chases and recesses shall not be cut in hollow walls, cavity walls, or walls of hollow masonry units, but when permitted may be built in. l?-4. Lintels and Arches.

(a) The masonry above openings shall be supported by arches or

lintels of metal or masonry, plain or reinforced, which shall bear on the

wall at each end for not less than 4 inches. Stone or other nonreinforced masonry lintels shall not be used unless supplemented on

the inside of the wall with iron or steel lintels or with suitable masonry

arches or reinforced masonry lintels carrying the masonry backing.

(b) Steel or reinforced masonry lintels shall be of sufficient strength

to carry the superimposed load without deflection of more than 1/360

of the clear span.

(c) Masonry arches shall have at least 1-inch rise for each foot of span and shall be designed to carry the superimposed load. Proper

provision shall be made for resisting lateral thrust. 17-5. Separation of Combustible Structural Members.

(a) No wall of 8-inch nominal thickness shall be broken into, subsequent to building, for the insertion of structural members.

(b) A separation of at least 4 inches of solid masonry shall be pro- vided between combustible members which may enter walls from

opposite sides.

(c) When unprotected steel or combustible structural members

frame into hollow walls of thickness not greater than 12 inches, they

shall project not more than 4 inches into the wall and shall be so spaced that the distance between embedded ends is not less than 4

inches. The space above, below, and between such members shall be

filled solidly with burned-clay materials, mortar, concrete, or equivalent fire-resistive material to a depth of not less than 4 inches on all sides of the members.

(d) All open cells in tiles or blocks occurring at wall ends shall be

filled solidly with concrete for a depth .of at least 6 inches, or closure

tiles set in the opposite direction shall be used.

17-6. Beam Supports.—Beams, joists, girders, or other concentrated

loads, supported by a wall or pier, shall have bearing at least 3 inches

in length upon solid masonry not less than 4 inches thick or on a metal bearing plate of adequate design and dimensions to distribute

safely the loads on the wall or pier.

17-7. Corbelling of Chimneys.

(a) No chimney shall be corbelled from a hollow wall, cavity wall, or a wall built of hollow units.

(b) No solid masonry wall of less than 12-inch nominal thickness

shall be used to support a corbelled chimney. Corbelling shall project not more than 6 inches from the face of the wall, and individual

corbels shall project not more than one-third the height of the unit. 17-8. Cornices.—The centers of gravity of stone cornices shall be

inside of the outer wall face. Terra cotta or metal cornices shall be

structurally supported.
Bwilding Code Requirements for Masonry 19

SECTION 18. EXISTING WALLS

18-1. An existing masonry wall may be used in the renewal or extension of a building provided that under the new conditions it meets

the requirements of this standard and is structurally sound or can be

made so by reasonable repairs.

18-2. Existing masonry walls which are structurally sound but which

are of insufficient thickness when increased in height shall be strengthened by an addition of the same material not less than 8 inches in

thickness laid in type A mortar. The foundations and lateral support

shall be equivalent to those elsewhere required for newly constructed

walls under similar conditions. All linings shall be thoroughly bonded

into existing masonry by toothings to assure combined action of wall

and lining. Such toothings shall be distributed uniformly throughout

the wall and shall aggregate in Vertical cross-sectional area not less than 15 percent of the total vertical area of the lining. Stresses in the

masonry under the new conditions shall not exceed the allowable

stresses prescribed for composite walls in Section 3-2.

18-3. No existing wall shall be used for renewal or extension of a

building, or increased in height without specific written permission

from the building official. SECTION 19. ERECTION

19-1. Masonry shall be protected against freezing for at least 48 hours

after being laid. Unless adequte precautions against freezing are taken, no masonry shall be built when the temperature is below 32°

F on a rising temperature or below 40° F on a falling temperature, at the point where the work is in progress. No frozen materials shall be built upon.

19-2. Brick (clay or shale) laid in other than type D mortar shall be

wetted when laid unless their gain in weight resulting from partial

immerson flatwise in % inch of water for 1 minute is less than % ounce.

19-3. Except when carried independently by girders at each floor, no

wall shall be built up more than 25 feet in height in advance of other

walls of the building.

19-4. No masonry shall be supported on wooden girders or other form

of wood construction.

19-5. No timber, except nailing blocks not exceeding an ordinary

brick in size, shall be placed in masonry walls; but this shad not pre- clude the use, on exterior walls, for decorative purposes only, of

timber members against the masonry or set into the masonry to no

greater extent than permitted for chases.

19-6. During erection, walls shall be adequately braced.

APPENDIX

The Appendix consists of explanatory matter referring to various

parts of the recommended code requirements. It is not a part of the

American Standard Building Code Requirements for Masonry but is presented as background material for users of the standard. The

subdivisions of the Appendix are numbered to correspond with the

section numbers of the standard.
20 Miscellaneous Publications, National Bureau of Standards

1-3. Tests.—In other sections of the standard, requirements are

set forth covering the quality of materials to be used in buildings.

The purpose of Section 1-3 is to give the building official authority

to require tests of such materials in case there is reason to doubt their

quality or their conformity to the intent of the standard. Under the

provisions of this section the building official may require tests to be

repeated if a£ any time there is reason to believe that a material no

longer conforms to the requirements on which its approval was based.

For the most part the specifications referred to include standard methods of testing or refer to standard methods. The building official should insist on strict adherence to these standard methods in all official tests. Since differences in the chemical composition of the raw materials

from which the units are made may cause differences in the color or structure of finished masonry units, visual inspection alone should not

be considered a sufficient basis for rejection. 1-4. Second-hand materials.—Irrespective of the original grading

of masonry units, compliance with code requirements of material

which has been exposed to weather for a term of years cannot be

assumed in the absence of test. Much salvaged brick comes from the

demolition of old buildings constructed of solid brick masonry in

which hard-burned bricks were used on the exterior and salmon brick

as back up, and, since the color differences which guided the original

brick masons in their sorting and selecting of bricks become obscured

with exposure and contact with mortar, there is a definite danger that

these salmon bricks may be used for exterior exposure with consequent

rapid and excessive disintegration. Often a similar practice is fol- lowed with other masonry units. Before permitting their use, the

building official should satisfy himself that second-hand materials are

suitable for the proposed location and conditions of use. 1-5. Materials and methods of construction not covered in these

requirements.—Procedures for approving new constructions having

merit should be as simple as possible so that use of such constructions, when justified by available information or by readily ascertainable facts, will not be retarded unduly. If records of service per- formance covering a period of several years, or the results of laboratory

or field tests that either are similarly time-consuming or of prohibitive

cost, are required as proof of acceptability, the development and

utilization of improved or less costly materials and methods will be

discouraged. On the other hand, perfunctory or otherwise inadequate

investigations and requirements relating to novel constructions may

lead to unsafe structures.

It appears to be the concensus of experts that the desired objectives

will not be attained by insisting that all new construction proposed

for use be subjected to precisely the same kind of examinations and

tests and be required to conform to the same limitations. In many

instances, opinions of structural and materials engineers may be of more value in estimating the durability and other essential properties

of an untried construction than the results of simple routine tests. Accordingly, detailed directions for investigating the adequacy of new

constructions are not given, nor are all pertinent properties listed. A definite size of wall panels for structural tests and methods for con- ducting these tests are recommended in the belief that standardization
Building Code Requirements for Masonry 21

of these features will be of assistance in interpreting the results and

will tend to minimize the need of making separate tests in each of many different localities. Suitable methods of testing masonry walls are described in NBS

Report BMS2 [l]. 2 The provisions of Section 1-4 (e) limiting the allowable compressive

stress are not intended to apply to constructions built by usual methods and of materials conforming to the requirements of Section 2, even

if the units, for example, are of somewhat different shape than those

in common use. They are intended to apply to materials of unusual

composition and to composite constructions of dissimilar materials

for which there is not adequate information demonstrating suitable

strength, integrity, and durability under the conditions proposed for

use. For such new constructions it seems desirable to permit their use only with a factor of safety somewhat larger than is conventional

for masonry until their performance in structures has been demonstrated.

2. Reference to standards [2]. Modern, well-written building codes are characterized by a liberal use of nationally recognized standards. Through their use the code

writer benefits from the work of committees of national organizations

having much better facilities for gathering and evaluating data than

local committees can be expected to possess. Moreover, tne use of nationally recognized standards tends toward greater uniformity in codes throughout the country, an important consideration to designers, builders, and producers of material who do work in more than

one locality.

Although there are several methods of utilizing nationally recog- nized standards, a specific method of adoption by reference has been

employed in this standard.3 The standard is referred to by title, serial,

designation, year of adoption, and the name of the sponsor organization is given. Some critics of earlier drafts of the A41 standard favored

a more general reference to national standards by stating that the

standard "as amended from time to time" should apply. This

expedient is not regarded favorably by many authorities on the

subject, however, because of the possibility that the courts will refuse

to uphold an ordinance utilizing such a method of reference on the

ground of uncertainty as to what edition of the standard is meant,

and as an improper delegation of legislative authority. While this procedure might be suitable for an ASA standard that would be used

only as a reference document, the possibility that the ASA standard

might be copied verbatim into a local code had also to be considered.

Constitutional provisions affecting the adoption of standards by

reference vary in different States and legal opinion is somewhat divided on the question. Hence, it would be well for code writers to consult

the appropriate law officer before adopting any method of utilizing

nationally recognized standards, and to ascertain whether the pro- cedure has legal sanction in order to avoid possible later attack on the

method employed.

' Figures in brackets indicate the literature references at the end of this Appendix.

' For a discussion of the use of standards, see NBS Building Materials and Structures Report BMS19,

Preparation and Revision of Building Codes, by George N. Thompson, chief, Building Codes Section, National Bureau of Standards. The report is available from the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C, for 15 cents.
22 Miscellaneous Publications, National Bureau of Standards

Current editions of national standards are referred to in this publication. Since these standards are revised at frequent intervals, care should be taken that the latest editions are referred to when a code

is in preparation or under revision, to prevent the code becoming obsolete in this respect before it is in print. Between successive editions of the local code the building official should endeavor to put such revisions

into effect by rulings, by council action, or by whatever method is permitted in his locality for amendments to the code.

2-1. Durability of masonry units.

ASTM C 62-41 T (brick, clay or shale) provides essentially a

classification for durability. The classification by strength given in

the note to Section 2 (e) of this specification is the one used in this code.

From the standpoint of durability the grades of ASTM Specifications

for Sand-Lime Building Brick (C 73-39) are equivalent to the cor- responding grades of ASTM C 62-41 T [3]. Sand-lime bricks differ from bricks made from clay and shale in that the compressive and

transverse strengths of sand-lime bricks are much better correlated

with the results of durability tests than are the same properties of

bricks made from clay and shale. Like certain concrete units, highstrength sand-lime bricks tend to gain strength during laboratory

cycles of freezing and thawing.

Few, if any, data have been obtained on the durability of concrete

bricks tested as bricks. The results of numerous tests on mortars

and concretes warrant the conclusion, however, that the requirement

of 2,500 psi for compressive strength of the grade A brick of ASTM

C 55-37 will reasonably insure durability where exposures correspond

to those considered in this code. ASTM C 55-37 does not provide

a minimum age for test. It may be assumed, however, that the

physical requirements specified apply to material "at the time of

delivery." The objection to the use of concrete bricks at early ages

is based upon the observed tendency for excessive shrinkage rather

than upon low strength. Steam curing under pressure is considered

to be advantageous both from the standpoint of decreasing subsequent

shrinkage and increasing early strength [4]. Since temperature must drop below 32° F for freezing to occur, it follows that in those sections of the United States where temperatures

seldom fall below freezing, the degree of durability called for by grade

SW of ASTM C 62-41 T and ASTM C 53-37 and grade A of C 55-37

is unnecessary. Those portions of the South Atlantic States ex- cluding mountainous areas, the Gulf States, and the Pacific coastal

region would not require compliance with grade SW as far as re- sistance to frost action is concerned.

Laboratory experiments [5] also indicate that the effect of freezing

and thawing cycles in producing disintegration is related to the degree

of saturation of the test specimen while being frozen. The nearer

the water content of a porous body approaches complete saturation

(all pores completely filled), the greater the tendency to fail when

frozen. High saturations result from continuous contact with or immersion in water or intermittent wetting under conditions such

that moisture does not excape from the unit. Masonry in contact with water-bearing soil, as in a retaining wall or foundation, or parapet walls poorly protected on their horizontal surface and sealed

by a through flashing and an impermeable coating, such as oil paint

or bitumin, on one or both of the vertical surfaces, may be highly
Bwuding Code Requirements for Masonry 23

saturated. Numerous instances have been noted where disintegrai tion of the inside face of a parapet followed sealing.

When water is in contact with a surf ace of a dry unit, the tendency

is for the water to enter the unit by capillary suction. If there is enough water and the time of contact is sufficiently long, the water

will strike through from face to face, giving a degree of saturation

equaling or exceeding that resulting from a 24 hour submersion in water at room temperature. This wetting through from face to face

describes the condition of being "permeated," referred to in ASTM

C 62-41 T. In the absence of defective workmanship, masonry pro- tected from above by flashing and with only one vertical surface

exposed is unlikely to be permeated with water by ordinary weather.

An additional degree of safety results from the probability that

freezing weather will only occasionally follow a heavy and long con- tinued rain without some intermediate drying. In general, units with

high rates of absorption have correspondingly rapid rates of drying.

The probability of permeation is obviously affected by the amount

and nature of precipitation. Precipitation as snow would not introduce water into vertical surfaces. ASTM C 62-41 T takes account

of this probability by permitting the use of grade NW bricks for exterior exposure where the average annual precipitation is less than

20 inches. Disregarding snow as precipitation, that portion of the

United States west of a north and south line through the center of Kansas can in general be considered as having an annual precipitation

of less than 20 inches.

With respect to stone, the term "durability" should be understood

to include resistance to all weathering agents to wnicb the stone i& exposed, and in cases of steps, floors, etc., resistance to abrasion.

Weathering agents of most concern are heat, cold, moisture, and

atmospheric gases. The question of durability for a given stone can

usually be settled by examining structures showing the stone under

uses similar to those proposed. For such studies the stone producer or

local stonesetter should be called upon for a list of structures. Untried stones under consideration for important structures should

not be used before thorough testing in the laboratory.

2-14. Mortar requirements.

Water retention, one of the factors of workability of mortar is limited by the requirements of Section 2-14 (a). The measure of water retentivity is the flow of the mortar after suction for 1 minute,

expressed as a percentage of initial flow. In measuring the flow, a standard mold 4 inches in diameter at the base, is placed on a flow

table and filled with mortar. The flow table consists of a rigid frame

with a flat, circular metal top so mounted on a vertical shaft that it can be raised and dropped through a fixed height by means of a rotated cam. The mold is then removed, after which the table is dropped 25

times in 15 seconds through a height of % inch. The flow is the

resulting increase in diameter of the mortar mass expressed as a percentage of the original diameter (4 inches). Thus, a mortar flow

of 100 percent indicates that the diameter of the mortar mass after being subjected to 25 drops of the flow table was 8 inches.

In conducting the water retention test prescribed in Section 2-14 (a), the mortar is brought to an initial flow of from 100 to 115 percent and

is then subjected to a vacuum of 2 inches of mercury (section) for 1 minute, after which the flow is again determined. If the intial and
24 Miscellaneous Publications, National Bureau of Standards

final flows of the mortar were 110 and 77 percent, respectively, the

water retentivity (flow after section) would be 77/110X100, or 70

percent.

A mortar is workable if its consistency is such that it can be placed

and spread with little effort but, on the other hand, is not so liquid

that it deforms under its own weight or flows out of vertical joints.

The property of adhering to a vertical surface or to the underside of a horizontal surface would be considered a factor in workability by

the mason. Other things being equal, the water content of the mortar

controls flow, which, in turn, is a measure of the consistency of the mortar. The practical application of the water-retention test is its simulation of conditions under which masonry is laid. When mortar is spread in contact with a dry, absorptive brick, for example, the tendency is for the brick to remove water from the mortar by capillary

action. In the water-retention test this process is simulated by

applying suction to the sample. A mortar of poor water retentivity

is objectionable for three reasons: (1) Removal of water througn

contact with absorptive units so stiffens the mortar that the joint

cannot be controlled and leveled, (2) water retentivity is so well

correlated with Workability that it can be assumed that poor water

retention means poor workability, apart from the use of absorptive

units, and (3) mortars that stiffen rapidly when in contact with

absorptive units will not make intimate contact nor bond well with

these units unless brought into contact more rapidly than is customary

in practice and thus will result in a weak bond and leaky joints

[6]. Usually the ingredients of mortar, other than organic admixtures,

that add to its plasticity also promote its water retentivity.

In Section 2-14 (b) the upper limit of not more than 3 parts of aggregate by volume to 1 part of cementitious material (sum of portland cement and lime, or masonry cement) is set to minimize: (1) harsh-working mortar resulting from over-sanding, with resultant

defective workmanship, (2) excessive weathering of the mortar, and

(3) lowering of strength. Since the volume changes resulting from

wetting and drying of hardened mortars are greater for rich than for lean mixtures, the minimum ratio of aggregate to cementitious

material is limited to 2. 2-15. Classification of mortar. The strength of a mortar serves as a convenient approximate indi- cation of other properties, such as durability. Although the strength

of masonry is not directly proportional to the strength of mortar, an

increase in mortar strength is associated with an increase in masonry

strength where other factors remain unchanged. Strength of mortar

has therefore been specified as one of the requirements, in addition to the two given in Section 2-14, that are intended to insure a workable,

durable, and satisfactory mortar for the locations set forth in Section 2-16.

The strength classification in Section 2-15 (a) represents the minimum strengths that may be reasonably expected from cement-limesand mortars of the proportions indicated in Section 2-15 (b) mixed

with sufficient water to give "mason's consistency" and using plastic

lime putty. The use of lime as hydrate may be expected to increase

materially these strengths.
Bwilding Code Requirements for Masonry 25

Optional methods of classifying mortar are presented in Sections

2-15 (b) and 2-15 (c). The proportions given in Section 2-15 (b) are those commonly used in building construction and for which there

is sufficient laboratory experience to establish the classifications. To

provide for the two usual methods of job proportioning, that is, by

sack measurement or by cubic-foot measure, a range has been given in the proportions, since a sack of hydrated lime may contain 1% cubic

feet. The note following the table provides information on the weightvolume relation of mortar materials.

The composition method of classifying mortars given in Section

2-15 (b), although perhaps adequate for the majority of jobs, does not

take into account the variation in mortar ingredients nor the wide

range in properties of masonry cements. A given masonry cement

may be a mixture of portland cement and hydrated lime; a hydraulic

lime; a natural cement; lime plus a puzzolanic material, such as slag; a portland cement diluted with limestone dust; or all of these with or without various admixtures, the presence of which may greatly

modify properties. Compressive strengths at 28 days have been

reported [7, 8] as covering a very wide range for mortars made from

commercial masonry cements. The same investigators reported a comparable range in durability as measured by resistance to freezing

and thawing.

To meet the objections inherent in the composition method of classi- fying mortar, an alternative method is provided in Section 2-15 (c), in which the strength classification is determined by tests made in accordance with specified methods. The requirement assumes that a request will be made to classify a mortar of given proportions in one

of the four classes specified in Section 2-15 (a). The decision of the

building official as to the proper classification may be based upon an

investigation of the claims for the given mortar, or he may accept duly

authenticated reports from recognized sources. In either case it is the intent of the requirement that samples be prepared in the laboratory from materials representative of those to be used on the job, and

in the given proportions. The test cubes should be cured as provided

in Section 2-15 (c) and tested in accordance with the prescribed test method.

No provision has been made in this section for a check test by the

building official on samples of mortar taken directly from the job.

Two reasons entered into the committee's decision on this point. One

was that it would be necessary to determine the classification of the

mortar prior to starting the job in view of the 28-day curing period of the test. The second reason was that the check test was considered

to be an administrative matter that would be covered in detail in the

administration section of a complete code and was therefore not

strictly within the scope of the project. Section 1-3 provides in

general terms for such check testing as the building official may deem

necessary and is intended to provide authority for the building official to test mortar classified under the provisions of Section 2^15 (c) if he

has any doubt as to whether the mortar continues to meet the classi- fication during the progress of the job.

2-16. Types of mortar required.

Type A mortar is characterized by rapid gain in strength, high

strength, and high modulus of elasticity and, when used with units of
26 Miscellaneous Publications, National Bureau of Standards

low rate of absorption, gives high bond strength. For these reasons type A mortar is required for foundation walls of hollow masonry

units and 10-inch cavity walls, which may not have adquate lateral strength if constructed with weaker mortars. To assure that a new

masonry lining of an existing wall will be effective in preventing the

overloading of the latter, it is essential that the masonry of the lining

does not undergo large elastic and plastic deformations, even when

loaded at an early age. Type A mortars are required for such linings,

because they quickly attain a relatively high modulus of elasticity and

do not undergo excessive plastic deformations under the allowed

stresses. Type B mortar, having a compressive strength of not less than 600

psi at 28 days, is considered to have satisfactory durability and

strength for use with solid units below finished grade, for load-bearing

and exterior walls, and for general use except in those locations and for the kinds of construction for which type A mortar is specifically

required.

Type C mortar has a low resistance to frost action when saturated

and hence is not recommended for use in locations in which the mortar

will be in contact with the soil. Its use is permitted in exterior and

interior walls of solid masonry, in interior nonload-bearing walls or

partitions of hollow units, and in other locations for which type A or type B mortars 'are not specifically required.

Mortars of type D ordinarily are slow setting and develop a moderate strength and resistance to weathering oniy after long aging under

favorable conditions. They may soften if kept wet. Because of their

very low strength at early ages and uncertain resistance to weathering,

they are not recommended for use in parapet walls, rubble stone walls, of where in contact with the soil. To compensate for the low resis- tance to lateral forces of walls built with type D mortars, lower limits on height and on spacing of lateral supports are recommended than

for walls built with stronger mortars.

3. Allowable stresses in masonry.

Recommended allowable compressive tresses are given for several

varieties of masonry, the values depending upon the type of mortar

and for some varieties upon the strength of the masonry units. Whenever justified by the available information on the strength of masonry,

the allowable stresses are the same for masonry of two or more types of

units, thereby avoiding unwarranted duplication. The grouping

chosen appears to be the simplest compatible with design stresses that

will afford reasonable assurance of safety without being the cause of

uneconomical construction.

Although the compressive strength of nrasonry depends upon several factors [9, 10] in addition to the strengths of the units and mortar,

the posible effects of the other factors on strength of masonry are minimized by limitations in the code and in the specifications f the materials'. For example, variations in strength resulting fr> differences in bonding, dangerously unfavorable curing, or extre values of height and thickness of members are limited by requireme

pertaining to these factors. Moreover, specifications for masoi

units include requirements on size, shape, and uniformity, as v as on other significant physical properties. To an important degi

therefore, much of the otherwise possible uncertainty about strenj
Building Code Requirements for Masonry 27

is reduced for masonry conforming to the requirements of this standard.

Quality of workmanship also has an important effect on the compressive strength of masonry. Highest strengths are obtained with

masonry having completely filled mortar joints, and with the bearing

shells and webs of hollow units alined in all courses Hi, 12]. This

kind of workmanship is difficult to obtain with some units, costs more than " commercial" workmanship, and rarely is found throughout the masonry portions of buildings. The committee agreed that

allowable stresses should be based on commercial workmanship,

which has been described as being representative of what is generally

obtained in commercial construction, where close supervision is not

to be expected and the most cogent consideration is economy.

The allowable stresses given in the several subdivisions of Section

3 are for the most part approximately the same as those recommended

by the former Building Code Committee of the Department of Commerce [13, 14]. In the absence of test data the allowable stresses

for type C mortar have been interpolated.

The specifications for hollow masonry units (Sections 2-4, 2-5, and

2-10) include requirements not only on minimum compressive

strength but also on the features of design (shape) of the units that

have an important effect upon the compressive strength of masonry

walls. These requirements (which apply to end- and to side-construction structural clay tile, to glazed building units, and to hollow

concrete units having face shells of different thicknesses) are such

that the minimum compressive strengths are approximately the same

for walls built with hollow units of each type covered by these specifications. For this reason, requirements on the design of the units are not included in the A41 standard and the recommended allowable

stresses are the same for masonry of the various types of hollow units.

The recommended stresses differ but little from those allowed by most

of the codes which do not include more restrictive limitations on

the units.

3-1 (b). Higher stresses. The maximum stresses recommended in Section 3 were selected

after a consideration of the unregulated or uncontrollable elements

affecting the strengths of materials. However, as conditions of use and standards of quality are better defined and controlled, the factor

of safety may be reduced. Hence, in order to take advantage of improvements in materials and methods of construction, authority

has been given to the building official to permit higher stresses in

design, upon a satisfactory showing that materials of a higher grade

or workmanship superior to that found in generally accepted good

practice will be employed under approved inspection.

It has been suggested that this provision might subject the building

official to pressure from groups intent on gaining an advantage for a given material. The committee recognized this possibility, but it was of the opinion that some discretion must be given to the enforcing

official if building codes are to \>e kept flexible to meet changing

conditions. The former Building Code Committee of the Department of Commerce in its report Recommended Minimum Requirements for Masonry Wall Construction [13] permitted an increase of 50 percent in the allowable compressive stresses for brick masonry
28 Miscellaneous Publications, National Burtau of Standards

under specified conditions of workmanship and where the effects of

all loads and forces were considered. It appears, however, that the

increased stresses have been written into some local codes without

these qualifying provisions. To avoid this, the committee has

refrained from recommending any specific increase in stresses and

has made the matter discretionary with the building official when

satisfactory evidence is produced that higher stresses are justified.

In passing upon such evidence, the building official should examine

carefully the conditions under which the tests which support the

claims for increased stresses were made. Both the size of the -test specimen [15, 16] and the type of wo kmanship employed have an important bearing on the results obtained. Tests of miniature specimens, such as two units and a mortar joint, would be of comparatively

little utility in predicting the strength of walls. Test assemblies

should be truly representative of the workmanship and materials

to be employed in the construction for which the higher stresses are requested.

The allowable stresses in Sections 3-3 and 3-4 are based upon results

of tests of masonry laid with workmanship approximating that generally obtained in commercial construction. For brickwork, this type of workmanship is characterized by deep furrowing of the horizontal

joints. For hollow masonry units, horizontal bedding is limited to the face shells. Workmanship characterized by full, level bed joints

and filled longitudinal and end vertical joints has been shown [11, 17] to increase the compressive strength of brick masonry from 25 to 100

percent compared with the strength of the masonry built with fur- rowed horizontal joints. Significant increase in strength for tile and

block results from increase in bearing of the bed joints [18]. 3-2. Composite walls.—Limiting the allowable compressive stress

in a composite wall to that allowed for one of its vertical elements seems

to be a reasonable restriction, although the results of some tests [18] under short-time and concentric loading indicate an average strength

somewhat higher than the strength of the weaker element. In service

the portions of a wall composed of dissimilar materials may undergo

unequal movements with change in temperature and moisture content

and thereby cause lateral distortions and a varying distribution of

stresses under constant load. However, long experience with faced

walls and with structures composed of different types of masonry

materials indicates that such movements are not large enough to endanger the stability of walls built in accordance with these recommendations. Another reason for this requirement is the fact that the

resistance of a wall to lateral loads, causing tensile stresses in the weak

element of a composite wall, depends largely on the tensile strength

of that element.

4. Lateral support.—Section 4 means in brief that if vertical supports, such as columns, piers, or cross walls, are provided not more

than the specified number of times the wall thickness apart, there need

be no limits on the distance between floors, or that when floors are spaced not over the specified number of times the wall thickness

apart, piers or other vertical members which afford lateral support

are not required. It is assumed that walls will be anchored to floors, as required by Section 17-2.

5-1. Thickness of solid masonry bearing walls.

It is common in some parts of the country to designate the thickness

of brick walls as 9, 13, and 17 inches, but a more general method is to
Building Code Requirements for Masonry 29

use even figures, such as 8, 12, and 16. The latter method is believed

to be more nearly in accord with the actual measurements and has

been used in the requirements. The figures are, however, qualified

, by the term "nominal," in recognition of the fact that there are unavoidable variations in mortar joints and in size of bricks. ASA

Committee A62 on the Cordination of Dimensions of Building Materials and Equipment has proposed two standards: (1) The General

Basis for Dimensional Coordination, A62.1, and (2) the Basis for the

Coordination of Masonry, A62.2. The latter standard contains the

provision that actual sizes of masonry units shall be based upon established nominal sizes which are equal to the actual dimensions plus the

thickness of a mortar joint. Application standards establishing the

modular sizes of masonry units are now being prepared, and when

these modular sizes are used in masonry construction, the actual thick- ness of walls will be equal to their nominal thickness (2, 4, 6, 8, 10,

12, and 16 inches) less the thickness of a mortar joint which, as provided in the definition of nominal, cannot exceed % inch.

No limit has been placed on the height of solid masonry walls, since

economic rather than structural considerations will control this. In unusual cases where bearing walls exceeding this height are used,

special care should be employed both in design and workmanship.

In a survey reported by the National Bureau of Standards in 1923,

41 percent of the local building codes examined permitted construction of two-story dwellings with 8-inch exterior brick walls. In 1937,

another survey made by the same agency showed 84 percent of codes

examined permitting such construction. With such a substantial

increase in use, it may be said that the 8-inch wall for dwellings is now firmly established. A further step has been taken in the requirements in permitting 6-inch walls for single-family dwellings and

private garages of limited height. It is recognized that such a wall

thickness will require a special unit, and it is understood that these

are in process of manufacture. The committee believes that, within

the limits specified, such units may be used with safety.

# Some building codes establish limits of span for floors supported by

bearing walls, requiring a greater wall thickness where such limits are

exceeded. This practice is believed to date back to the era when

working stresses for masonry were not limited directly, but by controlling the live loads likely to come upon the walls. When masonry

stresses are kept within the limits prescribed in Section 3, and lateral supports conform to the requirements of Section 4, the span of floor beams (within the limits imposed by other considerations) appears to be unrelated to the necessary thickness of masonry walls. In some places which are subject to high winds, trouble has been

experienced with thin masonry walls, but no evidence has been re- ceived indicating that the pressures resulting from maximum wind

velocities in most parts of this country have caused failures of enclosing

masonry walls having lateral supports in accordance with the provisions of Section 4. Neither an 8-inch nor a 12-inch wall of considerable height has the inherent stability to resist high wind pressures but,

if the building enclosed possesses sufficient mass and stiffness to resist collapse as a whole, it appears that walls having thicknesses within

the limits prescribed in Section 5-1 have sufficient resistance to withstand all but the most severe winds.

5-2. Thickness of solid masonry nonbearing walls.—It is especially

important that exterior nonbearing walls be well anchored to floors
30 Miscellaneous Publications, National Bureau of Standards

or other members providing lateral support, since they do not gain

added stability from superimposed loads, as in the case of bearing

walls. Details of anchorage are discussed under that heading in Sections 17-1 and 17-2.

5-3. Bond.—The requirements for bond in this section are some- what more liberal than in many existing codes. A common requirement has been that in brick walls at least every sixth course shall be a header course or there shall be at least one full-length header in every

72 squares inches of wall surface. The data [16, 19] are somewhat

contradictory as to the effect on compressive 'strength of masonry of increasing or decreasing the number of header courses. Some tests

[20, 21] indicate that highest strengths are obtained under central

loading with masonry having no headers. Headers are needed to cause common action of the vertical elements of walls under lateral loads and they assist to distribute eccentric loads, but both the results

of laboratory tests and service records of structures indicate that the

number required by many existing codes could be reduced substantially without having a practical effect on the strength or stability of masonry.

6-1. Thickness and height of walls of structural clay tile or hollow

concrete masonry units.—Although some codes limit the height and

use of 8-inch walls more than is done in the present standard, experi- ence, particularly within the last few years, has shown that the limitations established in the standard are satisfactory. Considerations

that entered into the decision concerning these walls included the fact

that requirements for lateral support provide adequate stiffening and

that, in the case of occupancies having heavy floor loads, such loads

increase the vertical components of the applied pressure and add to the

stability against lateral forces. 7-1. Thickness of solid walls of plain concrete.—In view of the

fact that the thickness of walls of plain concrete may be controlled

by the spacing of forms and that a somewhat greater stress in compression is permitted than for masonry of solid units, the minimum thick- ness of walls of plain concrete has been set at 2 inches less than for walls

of solid units. This reduction does not extend to walls of 8- and 6-inch

thickness, however, since in the absence of information justifying the use of thinner walls the committee is of the belief that these dimensions

should not be further reduced.

8-1. Thickness of stone walls.—Required minimum thicknesses for walls of stone follow conventional practice as recorded in many local codes. Experience has demonstrated that the thicknesses given are adequate for walls conforming to the other requirements.

9. Cavity walls and hollow walls of solid units.—Code practice

varies in the method of treatment of hollow walls. Some codes classify

walls either as solid or hollow, the latter term denoting walls of hollow units as well as hollow walls of solid units and cavity walls. In other codes the term "hollow wall" applies only to the type that

provides air spaces between the units, but no differentiation is made

between the various types of hollow walls. The practice therefore is somewhat confusing, requiring frequent reference to the definitions to determine the type of wall to which the provisions apply.

In this standard, walls of hollow units are covered in Section 6

and the two types of hollow walls in Section 9. A distinction is made

between the two general types of hollow walls merely to avoid confusion, since the requirements are substantially the same for either
Bvoiding Code Requirements for Masonry 31

type. The rolok-bak and all-rolok walls are examples of the hollow

wall of solid units in which the bond consists of masonry headers as

distinguished from the cavity wall in which the two tiers are completely separated except for the metal ties. The hollow wall of solid units formerly used to some extent in this country has largely been replaced in recent years by the cavity wall. The cavity wall has been used successfully in England for many years

and is reported at present to be the most commonly used type for housing. Limited in this country to houses and low buildings until

recently, the cavity wall has now begun to find use in panel walls of multistory buildings.

With cavity walls the loads are usually carried by the inner tier. The outer tier is customarily 4 inches thick and increases in thickness

are made in the inner tier. A nominal 10-inch cavity wall consists of two nominal 4-inch tiers and a 2-inch air space, or cavity. A nominal

14-inch cavity wal] consists of a nominal 4-inch outer tier, a 2-inch

cavity, and a nominal 8-inch inner tier. Tests at the National Bureau

of Standards [22] have shown that the 10-inch brick cavity wall loaded on both the facing and backing will support about the same load as an 8-inch solid brick wall. When loaded on the backing only, the 10-

inch brick cavity wall supported about 80 percent of the maximum

load carried by an 8-inch solid brick wall. Under transverse loading

the 10-inch cavity wall of either solid or hollow units has about onehalf the strength of the 8-inch solid wall [17, 22, 23, 24]. In view of the uncertainty as to the manner of loading cavity walls

in actual practice, and as a more convenient method of computing

the strength of the wall, the allowable stresses have been based on

the gross area of the wall. The allowable stresses have been reduced

from those permitted for solid walls to compensate for the increased

gross area provided by the cavity. The required net thickness of

cavity walls (exclusive of cavity) has been made the same? as that for

solid masonry walls but, to assist in obtaining adequate wind resist- ance, the use of type A mortar has been made mandatory in Section

2-16 for the nominal 10-inch cavity wall. The heights permitted by Section 9-2 are believed sufficient to

provide for the buildings which would ordinarily be built with this type of construction.

Because of the difficulty of covering all possible conditions, only

general requirements are set up in Section 9-5 for flashing. Since one

of the purposes of the cavity is to provide a barrier against the penetration of moisture, it is essential to provide flashing wherever the

cavity has been bridged for any purpose, such as heads and iambs of

openings, joist bearing points, etc. Where dampness prevails in the

soil against the foundation, a dampproof course should be provided

above the grade and below the underside of the first-floor construction

to prevent water from rising into the wall by capillarity [25]. Proper drainage should be provided at the base of the cavity to dispose of any water which might penetrate the cavity. This is sometimes accomplished by providing weep holes in the vertical joints

of the bottom course of masonry of the outer tier. The requirement

that the cavity shall be kept clear of mortar droppings is for the

purpose of insuring that the weep holes are not obstructed. The

mortar droppings can be collected on wooden slats which are placed on the wall ties, as these are laid and removed before setting the next

course of ties.
32 Miscellaneous Publications, National Bureau of Standards

9-4. Bond.

Ties in cavity walls serve as struts or tension members, causing the

two tiers to deflect about equally when a wall is subjected to bending

moments. However, the flexural rigidities of the usual types of ties are too small to transmit shearing forces large enough to cause the

two tiers to exert common action. Investigations have shown that

the resistance of steel wall ties to compressive and tensile loads depends

in part on the size and shape of the tie and the strength of the mortar

embedment [26]. These studies indicate that %6-inch-diameter rods

in mortar of type A or B have sufficient strength and stiffness to prevent excessive deformations.

Although there is some evidence that a useful life of 20 years or more may be obtained with steel ties having no protection against

corrosion, experience with such unprotected ties in this country has

been too limited to justify their general use. For most exposures and

types of structures, sufficient protection is afforded by coatings of coal-tar paint or of zinc or other corrosion-resistant metal.

The performance of cavity walls when subjected to lateral forces or to vertical loads on one of the tiers indicates that one tie for each

three square feet of wall area is all that is needed to assure substantially equal deflections of the two tiers of a cavity wall [22, 23, 24].

As the lateral forces may be more concentrated around openings, and

as resistance to these forces is less in these regions than elsewhere,

additional ties are required near the perimeters of openings.

10-4. Attachment of veneering.

The requirements for attachment of veneering have been intentionally stated in general terms in order to afford latitude in design.

Where more detailed requirements are desired, the following is deemed

to be good practice in satisfying the requirements of this section:

(a) For attachment of Drick veneering on masonry, one substantial noncorroding metal wall tie shall be used for each 300 square

inches of wall surface.

(b) For attachment of architectural terra cotta and other molded

units on masonry, one noncorroding metal anchor at least equal to %a-inch round, or % inch by % inch flat in sectional area, to each piece,

and two or more such anchors to all pieces over 18 inches in length

or more than 300 square inches in superficial area, except where such

architectural terra-cotta facing is bonded and completely filled with

the brick backing.

(c) For attachment of stone veneering on masonry, one noncor- roding anchor at least %6 inch by 1 inch flat, or its equivalent in cross- sectional area, to each piece over y2 square foot in face area, and at

least two anchors to all pieces over 24 inches in length or more than

400 square inches in superficial area.

12. Foundation walls. Some difficulty was experienced by the committee in arriving at a

satisfactory definition of this type of wall, and examination of a number of representative codes discloses considerable variation in

the meaning of the term. As commonly understood, however, a foundation wall is one that serves as a retaining wall in addition to furnishing support for the walls above, hence connoting underground.

It follows from this understanding of the term that the finished

ground surface marks in general the upper limit of the foundation

wall. However, since the wall between floors must be considered
Building Code Requirements for Masonry 33

as a unit, the term 1 'foundation wall" and the provisions applying

to it are intended to apply to the entire height of wall in the story

when any part of the wall is below ground level. For buildings on fairly level ground, the present definition is adequate. The main floor will usually be at or slightly above or below

the finished ground surface and the foundation wall will extend up

to that floor. Likewise, in the case of buildings built on sloping

ground, the front and rear foundation walls will extend up to the

floor nearest the finished ground surface. The side foundation walls

in such a case would extend up at least to the finished ground surface, although practical considerations will usually require that they

be of uniform thickness up to the floor nearest to the finished ground

surface in order to avoid an offset in the wall thickness in the exposed

face of the wall. From a structural standpoint, it is also desirable

that a uniform thickness be maintained up to the floor level, and such

a requirement is given in Section 4-5.

12-2. Minimum thickness of foundation walls. The committee is aware that in somewhat rare instances, foundation

walls conforming to the requirements of Section 12 may have insuffi- cient strength or stability to withstand the lateral pressures imposed,

and that, on the other hand, the requirements may be more restrictive

than needed for some structures and soil conditions. Aside from the

transverse strength of the wall [18, 27, 28], the factors which have the

greatest effect upon the lateral stability of a given wall are: (1) earth

pressure, (2) strength and rigidity of the lateral supports (usually the

footing and the first floor above), and (3) the vertical load on the wall. The lateral pressure may be zero, or it may approach the hydrostatic

pressure of a liquid having the density of mud. The probable maximum pressure for the foundation walls of a structure can be estimated

closely only by those familiar with the conditions at the site. Foundation walls of the materials and dimensions ordinarily used

are not stable against earth pressures unless restrained against horizontal movement at the top and bottom or along closely spaced vertical

elements. Usually the spacing of cross walls is too great for them to serve as the only lateral supports. Therefore, it is essential that the

floors be so anchored and connected as to restrain the top of the wall,

and that the bottom be restrained at the footing.

Vertical compressive loads on foundation walls resulting from the

weight of the building and its contents tend to prevent the development of or to reduce the magnitude of the vertical tensile stresses caused by lateral earth pressures. The resistance to lateral pressures

of a given foundation wall is therefore increased by an increase in the

weight of the superstructure. For example, if the maximum tensile stress in the foundation wall for a one-story light wood-frame house

were 20 psi, this stress probably would be reduced to 5 or 10 psi if the

superstructure were changed to a typical three-story house with

8-inch brick walls. The use of thinner foundation walls for light than

for heavy structures, as permitted by some codes, is not justified by a

consideration of lateral stability.

The transverse strength of walls of reinforced solid masonry not

only is greater than for similar nonreinforced walls but it is also more

uniform and reliable. The information available [24] indicates that

walls reinforced with %-inch round bars 2 feet apart, or the equivalent

in smaller bars or wires, has adequate resistance under all conditions
34 Miscellaneous Publications, National Bureau of Standards

commonly encountered. The heights of the back fill against other

types of 8-inch walls of unit masonry are limited to values related to

their expected resistance to lateral pressures.

13. Piers.—Tests have shown that when walls of hollow units are

built entirely with cells vertical and with webs carefully superposed,

their compressive strength is materially increased in comparison to walls of hollow units laid with the cells horizontal. Since it is believed

that filling the cells with concrete will help to insure the webs being

superposed, the increase permitted in Section 13 would seem to be

justified. The provision that unfilled piers of hollow units may be

used when their height does not exceed four times their least dimension

is intended to apply to minor structures, such as summer cottages and

accessory buildings.

15. Parapet walls. The provisions of this section are intended to regulate only the

structural features of parapet walls. Other standards in the series of

American Standard Building Code Requirements will specify when

parapet walls are required.

The limits on the ratios of height to thickness of parapet walls

specified in this section are believed to be safe for ordinary conditions. In localities subject to high winds or to earthquakes, somewhat more

rigid restrictions may be advisable. The committee recommends the

use of reinforcement as a means of preventing cracks or opened joints or the movement of the wall. Particular attention should be paid to the flashing, dampproofing,

j and workmanship of parapet walls to prevent disintegration.

Through flashing should be provided under the coping, unless the

coping is of an impervious material laid with watertight joints, and

also at the base of the wall. All joints should be well filled, and

exterior joints should be tooled with a round jointer. Coating, or

sealing, of the back of the wall with vapor impermeable materials is not recommended, as this practice prevents rapid drying of the

masonry.

16-2. Nonbearing partitions.—It has been pointed out by critics of

earlier drafts of this standard that the provision that partitions shall be built solidly against floor and ceiling construction is interpreted

by some building inspectors as requiring that steel wedges shall be used to wedge the partition tightly against the ceiling. Such is 1 not the committee's intent in the present section. The customary

practice of using small pieces of the partition material to wedge the

top of the partition to the ceiling and then slushing the joint full of mortar from both sides of the partition is believed to provide adequate

anchorage of the partition to the ceiling.

17-3. Chases and recesses.—The exception to the usual requirement that there shall be no chases in 8-inch walls is made to provide

for ducts of warm-air heating systems in dwellings, and for the recess- ing of radiators under windows. Since the grilles must be located

in exterior walls in many cases, and since the 8-inch wall is the com- j mon practice in dwellings, it was deemed necessary to provide space

in the wall for the elbow of the duct where it makes the turn from

the grille to the branch line located between the floor joists. The

committee was of the opinion that chases of the dimensions permitted \ in this section would not weaken the wall to any serious extent and

!
Building Code Requirements for Masonry 35

would permit of some economy and convenience in the installation

of the heating system. As no load of any importance is carried by

the masonry under the window sills, it was felt that recesses for radiators could safely be permitted under the conditions set forth in

ihis section.

19-1. Winter construction.—The procedures used in cold weather

concreting apply with little modification to construction of masonry

at temperatures below freezing. The recommendations for thawing

of aggregates apply to masonry units if exposed so that they contain

water, and freeze. The effects of low temperature on the setting and

the strength gain of mortars are similar to the effects on concrete. For more detailed information on this subject the reader is referred

to "Concreting in Cold Weather," Bulletin No. ST21 of the Portland

Cement Association, and to "Brick Engineering' 7 , published by the

Structural Clay Products Institute.

19-2. Wetting of bricks (clay or shale).

Evidence is available that the strength of bond in tension and in shear between mortar and masonry unit is related to the rate of suction

of the unit. [29] There is general agreement among investigators

that rates of suction exceeding 1 ounce per brick in the first minute

are associated with low bond strengths and with poor results on

water-permeability tests, and these difficulties are accentuated with

increasing rates of suction.

Evidence is also available that suitably wetting clay or shale bricks

of medium to high rates of suction increases the strength of bond

between brick and mortar and permits a more effective filling of joints as shown by reduction in permeability to water. A rough but effective test for determining what bricks give improved

bond by wetting consists in sprinkling a few drops of water on the

flat of the brick and noting the time required for these drops of water

to be absorbed completely. If this time exceeds 1 minute, wetting

is not needed. A refinement of this method consists in drawing a

circle 1 inch in diameter on the flat of the brick with a wax pencil

(using a 25-cent piece as a guide provides a circle of almost the exact

dimension). One milliliter of water (20 drops) is applied to the surface

thus limited and the time for complete absorption is noted [30]. If

i this time exceeds 1% minutes, the bricks need not be wetted; if less than 1% minutes, wetting is recommended.

Wetting of vitrified and semivitrified bricks or excessive wetting

of other bricks is undesirable because of resultant floating of the

bricks and "bleeding" of the mortar. A satisfactory procedure

consists in playing a stream of water on a pile of bricks until water

is observed to run from each individual brick visible in the pile.

Unless the bricks are exposed to conditions favoring the rapid evaporation of moisture, one wetting per day is sufficient. 19-3. Erection.—The vulnerability of excessively high masonry

walls to lateral forces before they are braced by floor or roof construction is not always taken into account in construction operations. Although the committee recognizes the danger of excessively high unbraced construction, it also appreciates that it is sometimes necessary

to build one wall to a full-story height before erecting other parts of the structure. A limit of 25 feet has therefore been set, coupled with

a provision that walls shall be adequately braced during construction.
36 Miscellaneous Publications, National Bureau of Standards

Construction to resist earthquakes

Through ASA Sectional Committee A58 on Building Code Requirements for Minimum Design Loads in Buildings, the attention of the

committee has been called to the desirability of certain specific provisions regarding masonry in areas where earthquakes are probable.

Items suggested for consideration include allowable types of mortar,

use of bond beams and columns, bonding of exterior veneer, use of hollow-unit masonry, and details of interior partitions. These matters are being given consideration and will be the subject of recom- mendations in a later edition of the committee's report. It is ex- pected that these recommendations, taken in conjunction with the

recommendations of Sectional Committee A58 as to design for re- sistance of horizontal forces, will provide a suitable basis for safe

construction in areas where earthquakes are a factor. REFERENCES AND NOTES 4

1] H. L. Whittemore, Methods of Determining the Structural Properties of Low-Cost House Constructions, NBS Building Materials and Structures Report BMS2 (1938) 10c.

[2] Specifications and standards referred to in these requirements are issued by

the following organizations. Unless otherwise indicated, the documents

may be obtained from the issuing organization. ACI Specifications (ACI):

American Concrete Institute, New Center Building, Detroit 2, Mich.

American Standards (ASA): American Standards Association, 29 West 39th

Street, New York 18, N. Y. ASTM Specifications (ASTM): American

Society for Testing Materials, 260 South Broad Street, Philadelphia 2, Pa.

All ASTM specifications referred to in these requirements may be found

in the ASTM Book of Standards, part II (1942). Reprints of individual

specifications may also be obtained from the Society. Federal Specifications (FS): Federal Specifications Executive Committee, Washington 25, D. C. Federal specifications may be obtained from the Superintendent of Documents, Government Printing Office, Washington 25, D. C.

[3] J. W. McBurney and A. R. Eberle, Strength, water absorption, and resistance

to freezing and thawing of sand-lime brick, J. Research NBS 20, 67 (1938)

RP1065 (5c).

[4] W. D. M. Allan, Shrinkage measurements of concrete block masonry, Proc. Am.

Concrete Inst. 28, 177-185 (1932).

[5] J. W. McBurnev and A. R. Eberle, Freezing-and-thawing tests for building

brick, Proc. Am. Soc. Testing Materials 38, pt. II, 470 (1938).

[6] H. C. Plummer and* L. J. Reardon, Brick Engineering, p. 61-70, (Structural

Clay Products Institute, 1943). Contains bibliography, review of test data and design information on brick masonry.

[7] J. S. Rogers and B. L. Blaine, Investigation of commercial masonry cement,

J. Research NBS 13, 811-849 (1937) RP746.

R. L. Blaine, Ten-year tests on commercial masonry cements, J. Research NBS

31, 45-53 (1943) RP1548 (5c).

[8] Results of Cooperative Tests on Masonry Mortars, Appendix to 1942

report of ASTM Committee C-12 on Mortar. Proc. Am. Soc. Testing

Materials 42, 266-270 (1942).

[9] D. E. Parsons, Specifications for hollow masonry building units, Proc. Am. Soc. Testing Materials 31, pt. II, 595-606 (1931).

[1.0] W. H. Glanville and P. W. Barnett, Mechanical Properties of Brick and

Brickwork Masonry, British Government Dept. of Scientific and Industrial Research. Building Research Special Report No. 22 (1934).

[11] J. W. McBurney, Effect of workmanship on strength of brick masonry, Am.

Architect 132, 613 (1927).

4 Where prices are given, the publications are available from the Superintendent of Documents, U. S. Government Printing Office, Washington 25, D. C.
Bwilding Code Requirements for Masonry 37

[12] Facts About Concrete Masonry, 8th edition (National Concrete Masonry

Assn., 33 W. Grand Ave., Chicago 10, 111.) (A discussion of effect of mortar bedding on strength of masonry walls is given on page 16 of this edition. The publication also contains summaries of test data and recom- mendations on design and construction of masonry. A reference index of the principal publications on concrete masonry is included.)

[13] Modifications in Recommended Minimum Requirements for Masonry Wall

Construction (1931). This is an amendment to Recommended Minimum

Requirements for Masonry Wall Construction, NBS Building and Housing

Publication BH6 (1924) 15c. An extensive bibliography of tests on masonry is contained in an appendix to this publication.

[14] A. H. Stang, D. E. Parsons, and J. W

T

. McBurnev, Compressive strength of

clay brick walls, BS J. Research 3, 50?-571 (1929) RP108. (The stresses recommended for brick masonry in the 1931 modifications [13] are based

largely upon the data in this report.)

[15] W. J. Krefeld, Effect of shape of specimen on the apparent compressive strength of brick masonry, Appendix to 1938 report of ASTM Committee C-15 on- Masonry Units. Proc. Am. Soc. Testing Materials 38, pt. I, 363-369

(1938) . [16] H. Kreuger, The strength of brick masonry. Tonind. Ztg. 40, 597-633 (1916). See also Clay Worker 68, 42, and 46 (1917), and abstract [page 8, 19]. [17] H. L. Whittemore, A. H. Stang, and D. E. Parsons, Structural properties of Six Masonry Wall Constructions, NBS Building Materials and Structures Report BMS5 (1938) 15c. Contains bibliography on the compressive and

transverse strength of masonry walls.

[18] F. E. Richart, R. P. B. Moorman, and P. M. Woodworth, Strength and

Stability of Concrete Masonry Walls, Univ. Illinois, Eng. Exp. Sta. Bui. No. 251. (1932.)

[19] J. G. Bragg, Compressive strength of large brick piers, Tech. Pap. BS 11 (1918)

Till.

[20] Stability of thin walls, British Government, Dept. Sci. and Ind. Research.

Bldg. Research Board Special Rep. No. 3 (1921).

[21] Page 536-37 of ref. 14 (comparison of compressive strength of "Ecoomy

Wall" with corresponding data on 8- and 12-in. walls built with similar brick and mortar).

[22] H. L. Whittemore, A. H. Stang, and J). E. Parsons, Structural Properties of a Brick Cavity

T all Construction, NBS Building Materials and Structures Report BMS23 (1939) 10c.

[23] H. L. Whittemore, A. H. Stang, and D. E. Parsons, Structural Properties of a Concrete-Block Cavity-Wall Construction, NBS Building Materials and Structures Report BMS21 (1939) 10c.

[24] H. L. Whittemore, A. H. Stang, and C. C. Fishburn, Structural Properties

of a Reinforced-Brick Wall Construction and a Brick Tile Cavity-Wall

Construction, NBS Building Materials and Structures Report BMS 24

(1939) 10c.

[25] H. C. Plummer and L. J. Reardon, Brick Engineering, p. 147. (See ref. 6.) [26] C. C. Fishburn, Strength and Resistance to Corrosion of Ties for Cavity

Walls, NBS Building Materials and Structures Report BMS101 (1943) 10c.

[27] A. H. Stang. D. E. Parsons, and H. D. Foster, Compressive and transverse

strength of hollow-tile walls, Tech. Pap. BS 20 (1926). T311 (15c).

[28] H. C. Plummer and L. J. Reardon. Brick Engineering, p. 98-102. (See ref.

6.) [29] L. A. Palmer and D. A. Parsons, A study of the properties of mortars and

bricks and their relation to bond, BS J. Research 12, 609-644 (1934) RP683

(5c).

[30] J. W. McBurney and A. R. Eberle, Further study of water penetrability of

clay and shale building brick, Bui. Am. Ceramic Soc. 17 [5], 210-216 (1938). Washington, February 15, 1944.

o