Designing for Building Maintainability - Effective Building Maintenance: Protection of Capital Assets - page 138

Also, experience shows that wood as a exterior wall material has signifi-
cant maintenance issues (wet rot, dry rot, etc.) and should be avoided,
especially in humid climates. Eliminatingwoodandmasonryaswallclad-
dingwillsigniicantlyreduceexteriorwallmaintenanceproblems .
What materials should be used as the cladding of exterior walls?
First, consider the use of precast concrete panels, which have approxi-
mately the same design service life as masonry materials, but with far
fewer maintenance problems. Precast concrete panels are denser than
brick or CMU and, thus, are better as water barriers. Installation is more
“engineered” and less dependent on the workmanship to produce a wall
without leaks, cracks, settlement, etc. that require maintenance. And,
from an aesthetic perspective, precast panels can be formed in many
different shapes and exterior finishes, yield significant design freedom
in their application.
Another good choice is prefinished, insulated metal panels. De-
pending on metal thickness and type of finish, metal panels can have
an anticipated service life as great as precast concrete, though typical-
ly will have a life expectancy about 30% shorter. Again, installation is
more “engineered” and less dependent on the workmanship to produce
a wall without leaks that require routine maintenance.
Finally, shorter life materials that should be considered include vi-
nyl, cement board, and metal cladding. These materials perform well
and require little maintenance over their design service life. And, at the
end of that life, they are relatively simple to replace.
Thefundamentalconceptinrainwatercontrolforwalldesignistoshed
waterbylayeringmaterialsinsuchawaythatwaterisdirecteddownward
andoutofthebuilding . Gravity is the driving force behind water drain-
age. The “down” direction harnesses the force of gravity and the “out”
direction gets the water away from the building. In general, the sooner
the water is directed out, the better.
Walldesignmustbebasedontheassumptionthatwatercanpenetrate
theexteriorinishorcladdingandenterthewall.
Every wall, therefore, must have a rain or water barrier applied
to the outside surface of the backing wall to ensure that wind-driven
rainwater does not penetrate the inner wythe of the wall. The exterior
cladding and be installed in such as way as to allow water to drain
to the exterior of the building. Then, a cavity or “drainage plane,”
with proper through-wall flashing and drain outlets, is always neces-
sary. Water that penetrates through cladding, then, will fall by gravity