Masonry Magazine August 1978 Page. 13
BRICK
CONCRETE BLOCK
4% SQ. FT. (0.42 m²)
MAXIMUM WALL
SURFACE AREA
PER TIE
2-SIDE WIRES AND RECTANGULAR TIES
MAXIMUM
VERTICAL SPACING
MAXIMUM
HORIZONTAL SPACE
Spacing and Staggering of Metal Ties
FIG. 2
REINFORCEMENT
CONTINUOUS
AT CORNERS
BRICK
CAVITY
BLOCK
3-SIDE WIRES AND SINGLE CROSS TIES
Continuous Prefabricated Joint Reinforcement
FIG. 3
CONCRETE BLOCK
CONTROL JOINT
DISCONTINUOUS
AT BOTH JOINTS
3-WIRE JOINT
REINFORCEMENT AT
16" (406 mm) 0.C.
VERTICAL
Corner Detail
Prefabricated Joint Reinforcement
FIG. 4
cases, there should be one wire on each shell of the
hollow block, with the third wire or rectangular tie in
the bed of the brick wythe.
Continuous horizontal wall reinforcement should be
properly lapped where necessary [a minimum of 8 in.
(203 mm)] in accordance with the recommendations of
the Concrete Reinforcing Steel Institute. To provide
additional continuity, the reinforcement should be car-
ried around corners, especially in the exterior wythe
(see Fig. 4). Horizontal reinforcement must be discon-
tinuous at all movement joints (see Fig. 5).
Typical types of wall ties suitable for use in cavity
walls, including continuous ties, are shown in Fig. 6.
Flashing and Weep Holes. Good flashing details are
an absolute necessity in cavity wall construction. In
order to divert moisture out of the cavity through the
weep holes, continuous flashing should be installed at
the bottom of the cavity, and wherever the cavity is
interrupted by elements such as shelf angles or lintels.
Flashing should be placed over all wall openings not
protected by projecting hoods and eaves. It should also
be properly placed at all window sills, spandrels and
parapet walls. Since the purpose of the flashing is to
collect moisture so it may be diverted to the outside,
weep holes must be provided wherever flashing is used.
Exterior flashing at a parapet is an exception to this
since its purpose here is to prevent water entrance, not
to collect moisture.
EXPANSION JOINT WITH
COMPRESSIBLE FILLER
AND SEALANT
BRICK
Expansion and Control Joint Detail
FIG. 5
Weep holes are located in the joints of the outer
wythe immediately above the flashing. Spacing of weep
holes should be approximately 2 ft (610 mm) o.c. maxi-
mum, except for those using a wick material which
should be 16 in. (406 mm) o.c. maximum (see Fig. 7).
Additional flashing discussion and details may be
found in Technical Notes 7 Series.
Shelf Angles. When the wall height or the number and
location of openings necessitate supporting the outer
wythe of a cavity wall on shelf angles attached to the
structural frame, it is recommended that horizontal
pressure relieving joints be placed immediately beneath
each angle. This is particularly important in reinforced
concrete frame buildings.
Pressure-relieving joints may be constructed by ei-
ther leaving an air space or placing a fully compressible
material under the shelf angle and sealing the joint with
a permanent elastic sealant (see Fig. 8).
When the exterior wythe of a masonry wall is sup-
ported on shelf angles, proper anchorage and shimming
of the angles must be insured so that they cannot rotate
and induce concentrated stresses in the masonry. A
small space should be left between lengths of angles to
allow for horizontal thermal movements and the holes
for anchor bolts should be horizontally slotted to allow
for greater ease of construction and any horizontal
movement.
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