Environmental Engineering Reference
In-Depth Information
caulking of breaks in the building envelope such as around windows and
doors (though most people in the U.S. believe that the reason one caulks
windows and doors is to reduce energy losses, the primary reason is to
prevent or minimize the penetration of rain water); and use of flat roofs on
nonresidential buildings (such roofs are at unusually high risk for water
intrusion episodes). Water leaks through rubberized membranes of flat-
roofed school buildings in the U.S. are widespread, as can be seen by the
numerous water-stained, and often mold-infested, tiles in drop ceilings. In
some cases, water-stained ceiling tiles are associated with other moisture
problems such as leaky air handling units, condensate from chilled water
lines, and plumbing leaks.
Water intrusion through the building envelope in residential structures
typically occurs through poorly installed or maintained flashing around
chimneys and exhaust structures in roofing, damaged roofing material,
poorly caulked windows and doors, and, somewhat surprisingly, brick and
stone veneer cladding. In the latter case, rain penetrates brick veneer through
tiny holes in mortar, cracks in bricks, and by capillary action through both
mortar and bricks. Mortar is relatively porous; bricks, less so. Water pene-
tration can be expected on the weather side of such buildings during wind-
driven rains, with subsequent movement of water vapor toward building
cavities by sun-affected thermal/physical forces.
Good construction practice requires that brick veneer be provided with
an approximate
3
/
4
” (19 mm) gap between its interior surface and adjacent
wall materials so that water that enters the cavity can trickle down to the
base where it can flow outward through functioning weep holes. A direct
pathway for moisture to wet wall materials is provided when masons do
not remove the excess mortar on the inside of brick or stone veneer. In other
cases, water may move by capillary action on metal ties from the brick veneer
wall to other components of wall structures. In many cases, masons fail to
include weep holes in brick veneer, or these holes are obstructed by excess
mortar which accumulates at the interior base of the wall during construc-
tion. Weep holes provide an avenue of egress for liquid water from behind
brick and stone veneer. They also provide a mechanism whereby air can
naturally enter the cavity behind veneer to remove moisture by convection.
On building sites with high shrink/swell-capacity soils, brick/stone
veneer wall cladding may develop settling cracks as it ages. These become
larger and more numerous with time. Not surprisingly, building age is a
significant risk factor for mold infestation, elevated indoor mold levels, and
health complaints.
E. Plumbing leaks and flooding
Water damage to buildings may occur as a result of small plumbing leaks,
as well as more infrequent episodes in which plumbing breaks cause major
floods in buildings. Small plumbing leaks are common and result in localized
water damage and often limited mold infestation (
Figure 6.9
)
. Small plumb-
