Masonry Magazine January 1979 Page. 17
Technical Notes
on Brick Construction
Brick Institute of America 1750 Old Meadow Road, McLean, Virginia 22102
21в
Jan./Feb.
1978
BRICK MASONRY CAVITY WALLS
DETAILING
INTRODUCTION
This is the third in a series of Technical Notes devoted to brick masonry cavity walls. Other Technical Notes in this series cover areas of cavity walls in general, including properties, design, material selection, and insulation; this Technical Notes is concerned with proper detailing.
The cavity wall can be correctly designed, and properly constructed using the best materials available, but if improperly detailed the wall will not function as it should.
GENERAL
Every structure must meet particular requirements and must be detailed accordingly. Details that are satisfactory on one structure may not be workable on another. However, certain details can usually be found that will minimize the possibility of damage to masonry walls from cracking, efflorescence, and water penetration. This Technical Notes will suggest some details which can be followed to achieve satisfactory cavity walls.
BOND BREAKS
Foundations
In many areas there are significant foundation movements which can cause severe cracking in walls rigidly attached to the foundation. If these walls are left free
FLASHING
WEEP HOLES
@ 24" (610 mm) O.C.
GROUT
BOND BREAK MATERIAL
PERIMETER
INSULATION FILLER
of the foundation, they tend to span the low points and thus reduce the cracking. In general, differential movements in foundations supporting cavity walls must be kept to a minimum, or serious distress may result. Differential movement of 4 in. (6.4 mm) in 15 ft (4.572 m) has been considered sufficient to cause cracking in masonry walls. However, observations on cavity type and other masonry walls have shown that differential movements in the foundation of more than 1/2 in. (12.7 mm) in 15 ft (4.572 m) could occur and yet the walls remain in good shape and have no cracks.
Figure 1 illustrates a typical foundation detail. In this case, the bond is broken between the base of the cavity wall and the top of the concrete beam by building paper. The transfer of movements in the foundation to the wall is thus minimized. Bond breaks also permit differential thermal and moisture movements without distress to either the brick wall or the concrete foundation. In addition, a bond beam or tie beam can be formed at the bottom of the wall by placing reinforcing bars and filling the cavity with grout. This will tie the inner and outer wythes of masonry together and distribute any strain over a longer length of wall. This can also be accomplished by a closer spacing of the horizontal joint reinforcement at the bottom of the wall. The above procedures will tend to contain any vertical cracks that may originate at the bottom of the wall.
When it is necessary to anchor the masonry wall to the foundation, it is still possible to detail the wall in a manner which allows some differential movement. Such anchorage may be required for load-bearing structures of high slenderness ratio or in earthquake design areas.
Foundation Detail
FIG. 1
BOND BREAK MATERIAL
3/16" (4.8 mm) DIAMETER
METAL TIES
Concrete Roof Slab Detail
FIG. 2