Masonry Magazine January 1977 Page.20
THICKNESS OF MASONRY
# General
Empirical design requirements pertaining to the thickness of bearing and nonbearing walls, and foundation walls are contained in Section 6 of the A41.1 Standard. Masonry walls must conform to these thickness requirements, some of which are quoted in the following paragraphs, as well as to the lateral support and allowable stress requirements which were discussed in previous sections of this Technical Notes.
# 6.2. Thickness of Bearing Walls
6.2.1. Minimum Thickness
The thickness of masonry bearing walls shall be at least 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, except as otherwise permitted in Section 6.2.3. Exceptions.
6.2.3. Exceptions
# 6.2.3.1. Stiffened Walls
Where solid masonry bearing walls are stiffened at distances not greater than 12 feet apart by masonry cross walls or by reinforced concrete floors, they may be of 12-inch 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.
# 6.2.3.2. Top Story Walls
The top story bearing wall of a building not exceeding 35 feet in height may be of 8-inch thickness provided it is not over 12 feet in height and the roof construction imparts no lateral thrust to the walls.
# 6.2.3.3. Walls of Residence Buildings
In residence buildings not more than 3 stories in height, walls other than coursed or rough or random rubble stone walls, may be of 8-inch thickness when not over 35 feet in height and the roof is designed to impart no horizontal thrust. Such walls in 1-story residence buildings, and 1-story private garages, may be of 6-inch thickness when not over 9 feet in height, except that the height to the peak of a gable may be 15 feet.
# 6.2.3.4. Penthouses and Roof Structures
Masonry walls above roof level, 12 feet or less in height, enclosing stairways, machinery rooms, shafts, or penthouses, may be of 8-inch thickness and may be considered as neither increasing the height nor requiring any increase in the thickness of the wall below.
# 6.2.3.6. Hollow Walls (Cavity or Masonry Bonded)
Hollow walls shall not exceed 35 feet in height except that 10-inch cavity walls shall not exceed 25 feet in height above the support of such walls. The facing and backing of cavity walls shall each have a thickness of at least 4 inches and the cavity shall be not less than 2 inches (actual) nor more than 3 inches in width.
# 6.2.3.7. Faced Walls
Neither the height of faced (composite) walls nor the distance between lateral supports shall exceed that prescribed for masonry of either of the types forming the facing or the backing.
# 6.3. Thickness of Nonbearing Walls and Partitions
6.3.1. Nonbearing Walls
Nonbearing exterior masonry walls may be 4 inches less in thickness than required for bearing walls, but the thickness shall be not less than 8 inches except where 6-inch walls are specifically permitted.
# 6.4. Foundation Walls
6.4.1. Thickness
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 allowable stresses. Foundation walls or their footings shall extend below the level of frost action and shall be not less in thickness than the walls immediately above them except as provided in Section 6.4.2.5. Foundation walls shall be at least 12 inches thick except as noted in Section 6.4.2. Exceptions.
6.4.2. Exceptions
# 6.4.2.1. Reinforced Masonry
Foundation walls of masonry units supported laterally at vertical intervals not exceeding 12 feet may be 8 inches thick if reinforced by means of vertical 6-inch diameter deformed reinforcing bars (or their equivalent) spaced not more than 12 inches apart and not less than 3½ inches from the pressure side of the wall; or 1½-inch diameter deformed reinforcing bars (or their equivalent) spaced not more than 24 inches apart and not less than 5 inches from the pressure side of the wall. Reinforcing bars shall extend from footing to top of foundation wall. Bars shall be lapped at least 30 diameters at splices. The space between each bar and the adjacent enclosing masonry surfaces shall be solidly filled with type A-1 grout or mortar.
# 6.4.2.2. Allowable Depth of 8-Inch Foundation Walls
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 may be 8 inches in thickness; cavity walls and walls of hollow units that do not extend more than 4 feet below the adjacent finished ground level, may be 10 inches and 8 inches, respectively, in thickness. Those 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 combined height of an 8-inch foundation wall and the wall supported shall not exceed the height permitted for 8-inch walls.
# 6.4.2.5. Foundation Walls Supporting Brick Veneer or Cavity Walls
Foundation walls of 8-inch thickness and conforming to the provisions of this section may be used as foundations for dwellings with walls of brick veneer on frame walls, or with 10-inch cavity walls; provided that the dwelling is not more than 1½ stories in height and the total height of the wall, including the gable, is not more than 20 feet. Foundation walls of 8-inch thickness supporting brick veneer or cavity walls shall be corbelled with solid units to provide a bearing the full thickness of the wall above unless adequate bearing is provided by a concrete floor slab. The total projection shall not exceed 2 inches with individual corbels projecting not more than 5 the depth (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 of headers at least 6 inches in length.
# 6.5. Parapet Walls
Unless reinforced to withstand safely the earthquake and the wind loads to which they may be subjected, parapet walls shall be at least 8 inches thick and their height shall not exceed three times their thickness.
BOND
# General
Bonding requirements (area and spacing of headers, or size and spacing of metal ties) contained in Section 7 of the A41.1 Standard differ only slightly with the bonding requirements included in the BIA Engineered Brick Masonry Standard. Some of the A41.1 Standard requirements for bonding are quoted below and major differences between these requirements and those contained in the BIA Standard are briefly described in explanatory footnotes.
# 7.1. Walls of Solid Masonry Units
Solid masonry bearing and nonbearing walls shall be bonded in accordance with Section 7.1.1, Bonding with Bonders or Section 7.1.2. Bonding with Metal Ties.
7.1.1. Bonding with Bonders (Headers)
The facing and backing shall be bonded so that not less than 4 percent of the wall surface of each face is composed of bonders (headers) extending not less than 4 inches into the backing. The distance between adjacent full length headers shall not exceed 24 inches either vertically or horizontally. In walls in which a single bonder does not extend through the wall, bonders from the opposite sides shall overlap at least 4 inches, or bonders from opposite sides shall be covered with another bonder course overlapping the bonder below at least 4 inches.
7.1.2. Bonding with Metal Ties
The facing and backing shall be bonded with corrosion-resistant metal ties conforming to the requirements of Section 7.6 for cavity walls. There shall be one metal tie for not more than each 41½ square feet of wall area. Ties "Section 5.8.2 of the BIA Standard permits a minimum lap of 3 inches.