WRB decision for cold weather situation
I’m doing a full gut/rehab on a 1950’s cape cod 1.5 story house in Nova Scotia, Canada this winter. I want to run my plan by you all to make sure i’m not wasting materials or choosing the incorrect ones.
I’m in zone 6 and will have an HRV for ventilation.
The house will be stripped down to the rough 1x sheathing, repaired where needed and covered with OSB.
Now for the WRB i’m considering doing Henry’s VP100 with their Hi-Tac primer due to the freezing temperatures (-5C to -15C) but i’m not sure if its needed or would be overkill since i’m putting 2 layers of foam on top. The alternative is Tyvek.
Window flashing will be Henry’s Air-Bloc LF liquid flashing encompassing the entire window bucks. The bucks will be 2 2×4’s with 3/4 XPS foam sandwiched in between.
Next comes 2 layers of 1.5″ GPS (Graphite EPS) with taped seams and 1×3 for the rain screen. Siding will be vinyl.
Windows are Triple pane casement
Walls are rough 1×4’s and will be insulated with fiberglass batts or open cell foam. (Figured fiberglass would work considering air-tight envelope)
No vapor barrier but if the building inspector forces the issue i’ll use Majrex or similar.
Basement walls will be closed cell foam at 2″ thick with 2×4 framed walls filled with fiberglass, headers will be 3″ foam with fiberglass.
Cathedral ceiling will be 7″ closed cell foam from top of the walls to the peak.
Please note that Zip sheathing is not available anywhere near me or i’d use that.
Fiberglass was chosen to keep costs down but may upgrade to open cell foam.
Heating system will be 2 x 12000 btu mini splits.
Water heater will be Rheem or similar heat pump. Sanden is out of budget
Thanks
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Replies
> Figured fiberglass would work considering air-tight envelope
It will work, but without interior side air sealing, there will be a some convective Winter airflow entering the walls up high, being cooled somewhat and then leaking back into the interior down low. No idea what it would come to in Btus.
Would this be mitigated with airtight drywall or should I just use a "smart" vapor retarder?
Hi David,
Sounds like you have a pretty solid plan in mind. Airtight drywall wil work. With fiberglass and other fibrous insulation, it is a good idea to air seal all six sides of the stud bays, including penetrations in the top and bottom plates.
Also, I have seen and heard about wavy vinyl siding as a result of installing it on furring strips and some manufacturers may not allow it. So, make sure that it is an acceptable installation detail with the brand of vinyl you are planning to use.
Finally, if you decide to go with Tyvek instead of the fully adhered Henry product, you'll need to air seal your sheathing with a combination of sealants and/or tape, but you probably already know that.
Thanks for the reply. I am concerned about the vinyl over the strapping as well so i'm going with a thicker than standard "Premium" vinyl.
Also would the Tyvek be required if sealing and taping all joints?
Edit: It appears Kaycan, ABTCO and the Vinyl Siding Institute accept the usage of strapping no more than 16" OC
Hi David.
If you go with a fully adhered WRB, it both provides a water and air barrier in one stop. Otherwise, tapes and such will air seal the sheathing and the mechanically fastened WRB (Tyvek) installed over the sheathing will provide the water barrier.
This is why builders like products like ZIP sheathing and fully adhered membranes. They minimize the steps and number of material to create water and air control outside of the sheathing.
@ Brian Pontolilo et al: in the case of Tyvek WRB, what is the benefit of air sealing when there will be 3" of taped EPS continuous insulation to the exterior? Doesn't all the work of air sealing the WRB become a bit redundant, and wouldn't 3" of EPS be considered a fairly considerable and reasonable air barrier on the exterior?
If I can reasonably avoid the Tyvek and just caulk and tape the OSB than I will. It just is not clear to me and I didn't want to waste materials.
Unfortunately ZIP sheathing is not found in eastern Canada and fully adhered WRBs are not suitable for cold weather unless you prime first.
It looks like taping and caulking and then using Tyvek would be the easier solution.
Should I bother with taping the seams on the foam? One layer or both?