House wrap debate. To wrap or not to wrap

[atvjoel]

I am sure we will get the wrap or your a POS guys out there, but would like to see honest debate about wrapping a house or not wrapping a house for areas that dont specify by code.

Cold climate here. Building a duplex. I am foaming my house with rigid poly spray foam. I have an opinion that I am oversealing the place even though the theoretical ideology with wrap is that it lets moisture out but not in. BUT I firsthand have seen mold developing BEHIND tyvek in the past. It has me tossed. I think if you are in wind zone without vinyl siding and using fiberglass r21 its good to install theoretically. Can I hear your thoughts?

Sh

 

[bill1952]

Hard to know without seeing complete exterior wall section but tyvek does not pass water, but does pass air which may be moist. If sheathing is plain OSB or ply, I'd want house wrap (my preference being 15 pound felt) under any siding. Other than vinyl siding, strongly prefer a rain screen.

Check out Building Sciences Corporation documents for some of the best research and thinking on this.

 

[TheCommish]

Competing requirments, the foam will cereantly be a wind/air barrier, dependin on the foam type and thickness may be a moisture barrier, then you need a water barrier, no sidding is a water barrier, vinyl leaks, brick weeps, wood seeps. If you dont use a wrap properly detailed, how is the water going be directed out of the wall siding interface be handled?

 

[Robert]

You do not want to create vapor barriers on BOTH sides of a wall....it will never breath. Tyvec is a vapor retarder, not a vapor barrior, so if mold was found behind it, I'm guessing it was because of what was installed over it was not properly detailed to weep or breathe as Commish mentioned. The code calls for WRB (weather resistive barrior), and many housewraps are considered wrb's. Use a rainscreen and follow mfr. rec

 

[steveray]

I am with commish....what is your WRB going to be?

 

[tbz]

Joel,

Personally, I prefer and use Zip panels for the sheathing system on the home, but as noted a properly installed WRB is worth its weight in gold.

house wraps are just one method, I would research what you have as options to get in your remote location and then weigh them against each other.

 

[SCBO1]

Our standard wall design was a 2x6 wall, with tyvek over OSB covered with LP sheet siding or lap. Inside the wall cavity was kraft faced R-19 with 1/2-drywall cover. We found out over the years that when polyethylene was used we had additional drywall nail pops. So we went to the kraft faced insulation with the kraft paper stapled to the inside of the stud. This wall performed the best for us when I was working for the constuction company, (the dark side).

I think the expandable foams have thier place but a design needs to be researched for your area, it maybe the best for your situation?

 

[bill1952]

Classic debate - staple face or sides. I think the manufacturers say either is acceptable, as is just friction fit - no staples - at least of the high density products. They acknowledge there are proclivities among inspectors. The requirement for "substantial contact" in some codes seems to sometimes favor face stapling.

I prefer unfaced and a heavy poly or better Tu-Tuf.

 

[Paul Sweet]

I also prefer 15 lb. felt (2 layers, shingled) over housewrap. If you go with housewrap it should be Tyvek or R-Wrap unperforated non-woven air infiltration barrier. Some of the big-box specials are perforated and will let water that gets past the siding into the sheathing.

 

[Genduct]

I am sure we will get the wrap or your a POS guys out there, but would like to see honest debate about wrapping a house or not wrapping a house for areas that dont specify by code.

Cold climate here. Building a duplex. I am foaming my house with rigid poly spray foam. I have an opinion that I am oversealing the place even though the theoretical ideology with wrap is that it lets moisture out but not in. BUT I firsthand have seen mold developing BEHIND tyvek in the past. It has me tossed. I think if you are in wind zone without vinyl siding and using fiberglass r21 its good to install theoretically. Can I hear your thoughts?

Sh

Sounds like your closed cell (?) Foam will take care of providing an air and vapor seal, but don't you still need a MRB (moisture resistant barrier behing your siding, Good Old roofing felt was the standard for generations.
I'ld ask your siding supplier what they prefer

 

[manifold]

Sounds like your closed cell (?) Foam will take care of providing an air and vapor seal, but don't you still need a MRB (moisture resistant barrier behing your siding, Good Old roofing felt was the standard for generations.
I'ld ask your siding supplier what they prefer

Closed cell spray foam will be an excellent air and vapor seal upon initial installation. But over the years the foam will shrink, the building will flex and shift slightly, and the foam will pull away from the edges of framing leaving myriad gaps for air/moisture to leak through. Spray foam should never be relied upon as the air or vapor barrier. Taped sheathing or membrane is the way to go.

Reason Foam Fails #5: Excessive Shrinkage

Fine Homebuilding, Feb/March 2012 With the growing use of foam plastic insulation in building construction, first in commercial roofing and then too often metastasizing over the entire building enclosure, it is being used increasingly as an air barrier component. This is a problem for many...

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