Wall assembly batt + insulated osb questions for climate zone 6
I am building a house this spring in Ottawa, ON Canada climate zone 6. I am trying to finalize my above grade wall assembly but am a little confused with what I read. My local building code requires an R22 batt and for me to use a vapor barrier on the inside of the wall assembly, but I have concerns of moisture/mold potential with the wall assembly I have chosen. Here is what I have planned thus far:
– 1/2 drywall
– 6mm poly vapor barrier
– 2×6 wall 16″oc with R22 fiberglass batt insulation
– Styrorail R7.5 OSB ( 1 7/8″ eps + 7/16″ osb)
– house wrap
– vertical 7/16″ furring strips
– horizontal 3/4″ strapping
– vertical vinyl siding
Online calculator is tell me I have a installed insulation of R30 and a effective thermal resistance of R20.33.
I do not see houses in my area having the osb seams taped, tyvek house wrap is installed over it and taped instead. Where as a zip sheathing is taped at the seams, the manufacturer of my insulated osb product doesn’t specify to tape the joints. They say to leave a 1/8″ gap between osb sheets and install a air weather barrier over it. Should I be taping the sheets of the wall assembly?
Should my exterior insulation be more / less substantial to avoid condensation in the wall cavity due to the dramatic temperature difference between seasons? My goal is to increase the energy efficiency of my home as much as possible, while still staying within a reasonable budget. Spray foam will be used around areas such as floor joist and rimboard area, or sealing exterior electrical boxes. The cost of using spray foam throughout the house will be too costly from my research.
Any help is greatly appreciated.
Dave
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Replies
Dave,
These wall assemblies which don't have enough exterior foam to keep the sheathing above the dew point work as long as they a built diligently. They aren't however as safe as those with enough foam.
https://www.greenbuildingadvisor.com/article/rethinking-the-rules-on-minimum-foam-thickness
Hi Malcolm,
Thanks for the reply. I read that and several other articles. So because my ridgid insulation is on the inside of my wall assembly, the osb due to extra insulation will be colder / wetter. So from what I gather I will need to be diligent on the interior vapor barrier detail to eliminate leaks. Should I be taping the osb sheathing even though an air barrier tyvek is used over the sheathing?
Dave,
Your primary air-barrier will be the interior poly. It never hurts to have a secondary one. That can be your sheathing, or the house-wrap if it is detailed as such.