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Community and Q&A

Air Sealing a Second Floor

sabotcat | Posted in General Questions on

I think this is super elementary, so forgive me. 

I’m designing our retirement home in California’s high desert and have set the whole “High Performance” thing in motion…which has been no easy thing with the resistance to new stuff I’m finding up there.  So I’ve kind of been leading the way in terms of external insulation, air sealing, etc.  

But one simple principle I can’t quite get my head around.  I can see air sealing the outside of the building.  I understand too the value of putting a 2x or OSB gusset on the top plate to allow you to turn the corner on the first floor ceiling with your smart vapor retarder. 

But how does one deal with the second floor?  Do you simply air-seal it independently?  sealing it’s own outside wall and ceiling?  It seems like you’d want to somehow seal the entire outer wall in a single monolithic way.  

I know there’s something I’m missing…and I always appreciate when you guys come back with links to articles.  If anyone can educate me on the piece I’m missing, I would truly appreciate it!

Yucca Valley CA

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  1. Expert Member
    Dana Dorsett | | #1

    Using the vapor retarder as the primary air barrier isn't the best practice. (Do you even need an vapor retarder in your climate? Which CA Title-24 or IECC climate zone are you in?) I'm pretty sure Yucca Valley is IECC zone 3B, which would not need or want vapor barriers.

    When building with plywood or OSB structural sheathing it's usually more reliable to detail the wood sheathing as the primary air barrier using material-appropriate tapes & goops. An exterior weather resistant barrier *(housewrap) would also normally be taped, as would any exterior rigid insulation as a "belt and suspenders" approach, but the air tightness integrity of housewrap (even fully-adhered housewrap like Blueskin or Vycor enV-S, etc) is easily compromised during construction and isn't nearly as rugged as plywood or OSB as the primary air barrier.

  2. sabotcat | | #2

    Thanks, Dana! That's super helpful.

    I've been digesting so many Wall models that I have to admit I never thought to wonder if they applied to us. We were going to build...from outside in: siding, furring strips, rigid insulation, wrb, seismic sheathing, 2x6 studs 24" OC with dense packed insulation, smart vapor retarder, service cavity, internal paneling.

    We're in 3B...but we see two or three fairly serious snows every winter. At 4500 feet our temps range from the high 20s winter mornings to about 100 a few days every August and September. I always thought, "belt and suspenders" would include a taped internal barrier of some kind behind the service cavity...but I may be watching too many Canadians.

    Does our altitude or temp variation change our approach at all? Honestly, if we can open the windows at night, the diurnal swings are so significant where we are that we end up with not too many cooling days in the summer and a fair amount of heating in the winter. Winter days may not get over 50.

    do you have a sense of best practices for our strange, dry, cold and hot environment?

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