Masonry Magazine August 2016 Page. 26
AIR BARRIERS
thing because sometimes water vapor
turns into liquid water as it cools to
its dewpoint, affecting hygroscropic or
water-sensitive building materials. For
example, wood rots, steel rusts and gyp�
sum crumbles.
This secondary benefit ofair barri�
ers -keeping wall assemblies dry �
while valuable indeed, is actually the
primary role of another unique bar�
rier: the water-resistive barrier (WRB).
WRBs predate air barrier usage in U.S.
construction codes by several decades.
Consistent with the concept that all
barriers are not created equal, it makes
sense that IECC building code require�
ments for air barriers are different than
IBC requirements for water-resistive
barriers. For example, the IECC allows
air barrier placement anywhere within
the thermal envelope. In contrast, the
IBC directs the installation of WRBs
over the exterior face ofsheathing.
By keeping sheathing dry after
water leaks past the primary cladding
2lOOF MSR I.SE
Jared Kennison Joe Kennison Sales, ext. 15 Sales, ext. 14
I
Dick Kennison Sales, ext 11
: � ' 0
Most sheathing and cladding manufacturers require the use of code�approved WRBs. It is also a requirement of the building code IBC Sec.
1404.2.
(and it will), the WRB, along with flashing, represents the second defense against water. The third defense against moisture remains the air barrier, which is designed to stop air that may be moisture-entrained and can poten�tially side-step the WRB, which may lack the inherent capacity to sufficiently retard moisture-laden air. Since WRBs are intended to stop water (not air), it should not be surprising that WRBs are tested to an entirely differ�ent set ofstandards than air barriers.
Despite the WRB's long-established role in keeping wall assemblies dry, sometimes an air or air/vapor barrier is mis�taken for a water-resistive barrier and installed in its place. Installing an air barrier in place ofa water-resistive barrier is a bad idea. I liken it to wearing flip-flops instead ofboots on a construction site.
Indeed, most manufacturers ofsheathing and cladding -the wall assembly components most often in closest prox�imity to an installed air barrier -make little or no reference to air orvapor barriers butinclude explicit requirements for a water-resistive barrier in their framed construction details, installation guidelines, and warranty literature. Lest these manufacturers' redundant pleas for a WRB are ignored, the lBC calls for the use ofan "approved" water-resistive barrier over sheathing (ICC-lBC 1404.2). Suffice it to say, mistaking the air barrier as the WRB is ill advised. Just because a par�ticular air barrier can be installed on a sheathed wall doesn't
24 I MASONRY � August 2016 � www.masoncontractors.org The Voice of the Masonry Industry