Page 11 - CodeWatcher Winter 2017 Issue
P. 11
Typical Wood Stud Wall Construction
Seven of the eight U.S.
climate zones recognized
by Building America occur in
the continental United States.
The sub-arctic U.S. climate zone,
not shown on the map, appears only in Alaska.
Figures R702.7 and R702.1 are excerpted from the 2015 International Residential Code Commentary, Copyright (C) 2015 International Code Council, Inc., www.iccsafe.org. All rights reserved. Excerpts reprinted with permission. Figure R702.7 International Energy Conservation Code (IECC) climate regions.
this figure they point out “Vapor Retarder” and that “In some Class ITIIAVBaLEpRo7r0R2.e7.t1arders
climates this process occurs in reverse.”
CLASS III VAPOR RETARDERS
To me, this is a warning to look into the assembly and
guidance in the code even more. CLIMATE CLASS III VAPOR RETARDERS PERMITTED FOR:a
ZONE
Seeking Details for Better Building
Vented cladding over wood structural panels.
Let’s focus on Climate Zone Marine 4; it’s the only “CZ 4”
that requires a Class 1 or 2 Vapor Retarder in this section. Vented cladding over fiberboard.
Marine climate is only in specific locations in the United
States: Western/Coastal Washington, Oregon and California Marine Vented cladding over gypsum.
(Refer to the Climate Zone Maps provided from EERE and in 4
the IECC.) For some reason, building industry professionals Continuous insulation with R-value ? 2.5 over 2 × 4 wall.
(builders, building officials, architects, insulation companies,
and others) default to including poly or kraft batts in these Continuous insulation with R-value ? 3.75 over 2 × 6 wall.
locations. This “default” is not always the best answer. Vented cladding over wood structural panels.
To go one more step further, in 2012 and 2015 IRC, Section Vented cladding over fiberboard.
R702.7.1 states “Class III vapor retarders shall be permitted
where any one of the conditions in Table R702.7.1 is met.” By 5 Vented cladding over gypsum.
venting the cladding or using continuous insulation in the
wall assembly you only need to use a Class 3 vapor retarder Continuous insulation with R-value ??5 over 2 × 4 wall.
like latex paint in lieu of Class 1 or 2. This section recognizes Continuous insulation with R-value ??7.5 over 2 × 6 wall.
materials in the assembly that slow vapor moisture transfer Vented cladding over fiberboard.
therefore gives flexibility in the assembly design. This table
still excludes Climate Zones 1 through 4 Except Marine. Vented cladding over gypsum.
6
As the song goes “I miss back when … The wind was all that
blew, And when you said I’m down with that, Well it meant Continuous insulation with R-value ??7.5 over 2 × 4 wall.
you had the flu…’. Terms we normally use in conversation
and the meanings that come along with them are not the Continuous insulation with R-value ??11.25 over 2 × 6 wall.
terms/meanings of today and can cause issues in our 7 and 8 Continuous insulation with R-value ??10 over 2 × 4 wall.
profession. I miss “Back When.” CW
Continuous insulation with R-value ??15 over 2 × 6 wall.
Stephen Carr is Regional Building Science Manager
For SI: 1 pound per cubic foot = 16 kg/m3.
for TopBuild Home Services. Have questions?
a. Spray foam with a maximum permeance of 1.5 perms at the installed
Email him at stephen.carr@topbuild.com thickness, applied to the interior cavity side of wood structural panels,
fiberboard, insulating sheathing or gypsum is deemed to meet the
continuous insulation requirement where the spray foam R-value meets or
exceeds the specified continuous insulation R-value.
Table R702.7.1
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