Sealing WRB penetrations from furring strips?
I’ve tried to read as much as I can, both on this site and in books by GBA contributors (PGH book, Martin Holladay’s book, and Allison Bailes’ book) but have not seen an anwer to what I’m wondering about. I’m a homeowner planning a new home build, not a builder.
I am currently planning: [plywood sheathing (hopefully with taped joints for air control)] + [WRB, taped/sealed as needed for staple-holes] + [exterior rigid mineral wool] + [furring strips to create rainscreen] + [vinyl siding].
However, the front elevation is required by the HOA to have stone veneer, — hence my plan for the rainscreen at least on that elevation, to guard against inward solar vapor drive from any stone veneer reservoir effect. And then I assumed that the rainscreen should be on all elevations.
Questions:
1. Is it recommened to maintain the furring + rainscreen on the vinyl siding elevations? (My understanding is that it may not be strictly necessary given that the vinyl siding is non-reservoir, and given that the mineral wool can dry out. But would it be a problematic asymmetry to have the rainscreen only on the stone veneer elevation?)
2. My understanding is that for air control, it’s recommended to seal the staple-holes on a stapled WRB (as per my understanding from https://www.greenbuildingadvisor.com/article/choosing-an-air-barrier-and-a-housewrap). What about penetrations made by screwing furring strips to the sheathing? Do those need to be sealed, and if so how?
3. Similarly, what about sealing the penetrations of the WRB made by screwing the rigid mineral wool to the sheathing? (My understanding of attaching exteriori mineral wool comes from https://www.greenbuildingadvisor.com/article/installing-roxul-mineral-wool-on-exterior-walls and https://www.greenbuildingadvisor.com/article/installing-mineral-wool-insulation-over-exterior-wall-sheathing)
Many thanks in advance for any information —
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Replies
otinkyad,
1. Vinyl siding performs fine without a separate rain-screen, and there is no disadvantage in having one wall assembly on some walls, and another on others.
2 & 3. As the article you linked to says, a WRB makes a poor air-barrier. You are better off choosing a different part of your assembly - (as you suggest) the sheathing, or an interior membrane being two good choices. Then you can concentrate on detailing the WRB for its primary function, which is to exclude water intrusion from the outside. Especially if the walls include a rain-screen cavity, small holes from fasteners aren't worth worrying about.
Malcolm,
Thank you very much -- this information is very helpful, and your kindness in replying greatly appreciated!
(I've also seen many other helpful replies from you in various articles on here, so thanks once again).
otinkyad,
You're welcome. It's not all altruism. Having to think about these things helps me immensely too.
I would keep the rainscreen behind the vinyl for fastening purposes. Otherwise you will need a long enough fastener to go through the mineral wool and into the sheathing. I think you’d have a better product with furring strips to fasten to.
I definitely agree with Malcom—tape the plywood and don’t worry about the fasteners going into the WRB.
ES_Builders,
Good point. I don't know what the cut off is where it becomes worth adding furring. Around 1 1/2" of exterior insulation?
Malcolm,
I would probably insist on the rain screen at the 1-1/2” mark. To be honest, I hardly ever work with vinyl, so I’m no expert.
ES_Builders and Malcolm -- Thanks very much for the further thoughts. For some reason I did not get notifications about replies, and so hadn't seen these additional responses of a couple of days.
So glad to have found this community. Without it I wouldn't even have known about the resources that I'm now using to try and educate myself (books by Lstiburek, Holladay, Bailes, etc) -- leave alone the articles here, and the direct help such as these responses.
Thank you all so much!