Building Design and Construction Handbook - Merritt - Ventech!

WALL, FLOOR, AND CEILING SYSTEMS 11.15
Recesses may be left in walls for stairways and elevators, but the walls should
not be reduced in thickness to less than 12 in unless reinforced in some approved
manner. Recesses for alcoves and similar purposes should have at least 8 in of
masonry at the back. They should be less than 8 ft wide and should be arched over
or spanned with lintels.
If the strength of a wall will not be impaired, pipe or conduit may be passed
horizontally or vertically through the masonry in a sleeve. Sleeves, however, should
not be placed closer than three diameters center to center.
11.3.7 Flashing in Masonry Walls
Flashing should be used to divert to the exterior of a building water that may
penetrate or condense on the interior face of masonry walls. Accordingly, flashing
should be installed in exterior walls at horizontal surfaces, such as roofs, parapets,
and floors, depending on type of construction; at shelf angles; at openings, such as
doors and windows (Fig. 11.6a and b); and at the bases of walls just above grade
(Fig. 11.6c and e). The flashing should extend through a mortar joint to the outside
face of the wall, where it should turn down to form a drip.
Flashing in tooled mortar joints, however, would trap water unless some means
is provided to drain it to the outside. Consequently, flashing should be used in
conjunction with weep holes, which should be formed in head joints immediately
above the flashing (Fig. 11.6d). When the weep holes are left open, spacing should
not exceed 24 in c to c. If wicks of glass-fiber or nylon rope, cotton sash cord, or
similar materials are left in the holes, spacing should not exceed 16 in c to c.
Materials used for flashing include sheet copper, bituminous fabrics, plastics, or
a combination of these. Copper may be selected for its durability, but cost may be
greater than for other materials. Combinations of materials, such as cold-formed
steel and plastic or bituminous coating, may yield a durable flashing at lower cost.
FIGURE 11.6 Flashing in masonry walls: (a) over an opening for a window or door; (b) under
a window sill; (c) at the base of a wall; (d) and (e) below weep holes.