Contractor won’t spray foam upper attic because I don’t have house wrap?
I was getting settled on having a contractor extend the vent baffles in my upper attic to the ridge vent and then apply OC foam w/ vapor barrier spray. This would air seal and bring the upper HVAC into the enclosure. I would do the lower triangular attics myself with air dams and foam board (following the details from building science that we’ve seen here around the cape-style house retrofit topics). The remaining few feet of space between knee attic and upper attic would remain FG & vent baffle (effectively dammed at soffit and ceiling/attic transition). This was my plan.
Contractor caught me mention that my house doesn’t have house wrap, and suddenly he’s concerned about moisture at the spray foam boundary- I think he means where the spray foam stops and begins, depend where you are in the attic, vaulted ceiling (that will remain FG & vent baffles and the upper attic spray foam will act as it’s upper air dam) or sloped ceiling then knee-attics (which I’ll have air sealed and enclosed in the conditioned space with the bays dammed off at the soffit entry).
I fail to see how house wrap makes a bit of difference in this equation. What am I missing? Is house wrap a factor, or besides that, and I missing anything else from a moisture control perspective?
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Replies
Can you ask that he explain his concerns in more specifics? He might view house wrap as the solution to an observed problem, but maybe you've addressed that same problem in another way. You should discuss said potential problem before you start ordering and installing specific materials.
What is your climate zone?
Do you have any housewrap/WRB or none at all?
What is your siding?
Is your interior dry? (I.e., do you have a wet basement or crawlspace?)
Michael,
Zone 4 *Kanawha Co, WV, border of the A/B and I forget which I am)
Lower house/ first story is brick except for a middle front wall. This wall is the only 2x4 wall in the house of significance that isn't masonry clad. No wrap that I know of at all. Just sheathing, vinyl siding on a main front wall. Upper is mostly roof and knee walls, with dormers (2x4 I believe no wrap, just sheathing and vinyl siding), and upper gable triangles which are 2x8 (yes standard 2x8 thickness, fairly large and wide. Walls are insulated with FG (yellow Certainteed).
Interior is about like you'd probably expect for an air-leaky (10.9 ACH50) house. Crawl space used to have water issues but I've done an encapsulation with sump pumps and a dehumidifier that keeps it at or under 55%.
I use a house stand up dehumidifier as of last summer to keep the interior under 60%. I am hoping that as I get it air sealed it will help contain and maintain control on the interior air. But this project was to be a part of that- might have to change course now.
With that, might you thinking my moisture issue I described might be as much through-wall permeance as it air exfiltration and replacement? A large chunk of the ACH50 leakage was from the knee attics around their access doors. Fairly low hanging fruit.
My main objective is to get the upper attic into the thermal envelope and air seal to a "pretty good" tightness. Maybe 5 or so is the goal.