Masonry Magazine April 2007 Page. 44
FLASHING AND
DRAINAGE
the sheet metal sections together. Sheet metals also tend to
be the most expensive flashing materials.
One of the most common materials used for flashing is
rubberized asphalt. It typically comes in variable width sheets
and is self-adhesive. The sheets are manufactured through care-
ful blending of rubberizing agents with asphalt (typically SBS
or SEBS). The rubberized asphalt then is laminated with a
backing material, usually high-density polyethylene. These
products are usually 40 mils thick, are flexible, easy to install,
non-corrosive, and will not absorb water. They are a somewhat
less durable than sheet metal since they are more susceptible to
punctures. However, since this type of flashing often is fully
adhered to the substrate, a puncture will not necessarily result
in a leak. Nonetheless, punctures should not be tolerated in any
kind of flashing installation. Laps and joints in rubberized
asphalt flashing materials are sealed through the self-adhesive
properties of the material.
Thin approximately 20 mils thick or less - polyethylene
sheeting (plastic) also is being used as flashing. However, this is
not a durable material. In such thicknesses, polyethylene has near-
ly no puncture resistance and will degrade over short periods of
time. Additionally, sealing joints and laps in thin polyethylene or
other types of plastic sheets is difficult.
There are many other types of through-wall flashing prod-
ucts such as laminated copper sheets. Before specifying any
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Masonry Detailing
Series Offers New
Design Tools
The new web-based Masonry
Detailing Series from the Interna
tional Masonry Institute (IMI) gives
building designers easy-to-use,
practical solutions for their
masonry projects. The interactive,
multimedia format includes draw-
ings, images, narratives, animated
details and more. To view the
series, go to www.imiweb.org/
masonrydetails/index.htm.
IMI also offers custom, project-
specific advice through its region-
al Technical Service offices, which can be reached at (800) IM-0988.
or www.imiweb.org
IMI offers free technical assistance to the design and construc
tion communities, professional education for masonry contractors,
and skilled training for craftworkers. IMI is a strategic alliance
between the International Union of Bricklayers and Allied Craft-
workers (BAC) and their signatory contractors to promote quality
masonry construction.
For more information on IMI, please visit www.imiweb.org.
flashing materials, they should be evaluated for their durability
and installation practicality.
Flashing accessories such as termination bars, drip edges,
solder, primers, adhesives and sealants must also be durable
and compatible with flashing and other wall materials. Metal
components must be non-corrosive and sealants must remain
soft and flexible. No material should adversely affect any other
material within the wall system.
Detailing
ALTHOUGH QUALITY mason contractors should fully
understand the purpose of flashing and installation requirements,
flashing systems should be thoroughly detailed on the construc-
tion drawings. These details should provide direction to the con-
tractor in forming end dams and corners, installing termination
bars and drip edges, sealing seams, providing expansion joints,
and installing proper flashing support.
Detailing flashing to collect and divert water from the interior
cavity wall surfaces to the exterior should consider the following
1) End dams must be used at the ends of each length of
non-continuous flashing to force water to the exterior
of the masonry cavity walls. The most common
location for end dams is at the ends of window lintels
and windowsills. Without them, water will flow along
and off of the end of the lintel into the wall cavity
(path of least resistance). However, since the window
lintel spans the full width of the wall cavity, water can
spill into the cavity at or near the interior walls,
exposing them to potential water penetration.
2) Proper detailing at corners is necessary to ensure
moisture does not penetrate through the flashing
system. Details for corners must indicate locations for
seams and laps. Corner details may include the use of
preformed sheet metal, even if rubberized asphalt
flashing is used.