Barrier
Mtech
| Posted in Energy Efficiency and Durability on
Hi good afternoon, just wondering if I seal my wood sheathing with tape. The 1/8 inch gaps on the exterior. Due I still need a vapor retarder on the inside? Like Membrain. I’m in zone 5 and using fiberglass batts or rock wool . Thanks
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Replies
M. Tech,
In Climate Zone 5, building codes require that walls include an interior vapor retarder (a less stringent layer than a vapor barrier). MemBrain will meet this code requirement, as will kraft facing or vapor-retarder paint applied to the drywall.
For more information, see "Vapor Retarders and Vapor Barriers."
I forgot to mention. Exterior will be brick and also plywood sheathing will be covered with 15lbs tar paper. Will that change response you gave me before. Thanks again.
The 1" air gap between the brick and #15 felt & plywood qualifies as "Vented cladding over wood structural panels" per TABLE R702.7.1, thus no MemBrain etc is required.
But if the roof overhangs are minimal, allowing frequent rain wetting of the brick it can bring on a separate set of problems if care isn't taken to ensure that there are both vents/ weep holes at the bottom and corresponding vents at the top of the brick veneer to promote convective purging of the air in that cavity. (Keeping the weep holes or bottom vents clear of dropped mortar is also advisable.) High moisture drives from sun heated wet brick would not be mitigated by an interior side vapor retarder. See:
https://buildingscience.com/sites/default/files/migrate/pdf/rr-0907_ventilated_wall_claddings_review_performance_modeling_rev.pdf
Search that document for all references to "brick" to get to the pertinent points regarding your wall stackup.
With deep roof overhangs and minimal wetting those venting details aren't as important, but still a good idea.
See also:
https://buildingscience.com/documents/information-sheets/reservoir-claddings
In Climate Zone 5 you do NOT need an interior side vapor retarder tigher than standard interior latex paint IF...
...you have, per "TABLE R702.7.1 CLASS III VAPOR RETARDERS" in the 2015 IRC :
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Vented cladding over wood structural panels.
Vented cladding over fiberboard.
Vented cladding over gypsum.
Continuous insulation with R-value ≥ 5 over 2 × 4 wall.
Continuous insulation with R-value ≥ 7.5 over 2 × 6 wall.
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The code definition of "vented cladding" can be vinyl siding, or any siding installed with a rainscreen/ air-gap between the siding & sheathing.
Wood structural panels includes typical OSB and plywood sheathing products.