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Code Cycle: 2016 & 2019 Standards
Because of the gap between the sheetrock and the insulation, using RC channels will cause a fail for QII. RC channels are used by running the channel across the indoor side of the studs and under the sheetrock for sound control or may be a requirement for the fire codes. Presumably, the goal is typically to stop sound transmission by creating a gap between the studs and the sheetrock, but it also creates a gap between the insulation and the sheetrock. Obviously, the purpose of having the insulation in contact on six sides is to prevent convective loops from happening.
See the CEC's suggestions below.
Suggestion 1: Put a thin, approved air barrier, such as Thermal-Ply over the studs, before the RC channel goes on, such that the insulation is in contact with this air barrier. This way, the sheetrock is not the inside air barrier.
Suggestion 2: Net over the RC channel and fill the voids. Or use SPF so that it fills all gaps behind the studs and around the RC channel.
Suggestion 3: Install R-19 batts (or some batt that is at least 4" thick), but leave the wall modeled as is (R-13 or R-15 cavity insulation). This way the insulation will be in contact with the sheetrock everywhere except the 1" wide space between the sheetrock and the studs. Even though there is a small void, I doubt it is big enough for substantial convective loops to form. Plus, the additional 1" of insulation everywhere else is probably more than an equal trade off.
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