Best housewrap between OSB and foam?
So I’m hoping to build a house with exterior foam over the OSB sheathing, and plan to go with “innie” windows, with the WRB between the foam and OSB. A draining house wrap is often recommended for this (“Mind the Gap, Eh!”). Tyvek has StuccoWrap and DrainWrap, Green Guard has RainDrop, Berry Plastics has WeatherTrek and Barricade Drainage Wrap. Others?
I was wondering what experience people have with various products, and if there is a reason to prefer one over the others, or to avoid any? Cost? Convenience? Effectiveness? Durability?
FWIW, the climate is Zone 4 Marine (mostly warm/dry summers, damp/cool the rest of the year), siding will be fibercement on a rainscreen, and foam type is currently undetermined.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Ian,
Are you the homeowner...the builder...or both?
Have you observed any local builders building with the method you described?
Or ....are you basing your choice on a published example? If so which project?
I’m the homeowner, haven‘t selected a builder. This site is a great resource, and I hope you all won’t mind seeing a lot of questions from me as I think about different aspects of the design.
Although I know some builders here use exterior foam, I don‘t know whether “innies“ or “outies” are the norm. I’ve thought about “outie” windows, with foam-as-drainage-plane or WRB over the foam (or both). But our architect likes the look of “innie” windows, and the Building Science “Guide to Insulating Sheathing” describes the WRB-between-foam-and-OSB arrangement as “the most durable assembly proposed in this guide as the drainage plane material (building paper or house wrap) is supported by the plywood sheathing, and protected against wind loading and other environmental factors by the insulating sheathing,” and an article I read about REMOTE mentions DrainWrap as an appropriate under-foam WRB in rainy cold climates.
On this site, DrainWrap, RainDrop, and WeatherTrek have been mentioned together a few times as draining housewraps appropriate for use between foam and OSB. I assume that any of these would work fine, but I was wondering if there was any reason to have a preference.
Hi Ian - I have not installed each of the wrbs you mention, although I have become pretty familiar with the general traits of each. Tyvek stuccowrap and drainwrap are essentially the same product. Raindrop is similar in feel to a feed sack you might find at a farm supply store. I believe its the only woven option in this category (although my information could be incomplete). Out odd the group, I really like theweatherdrop for its omnidirectional surface, so air can circulate on all directions, not just up and down. Now I'm no scientist, and don't have anything to go on but gut and what I've learned from forensic building scientists, but I tend to think (personally) that the surface of the weathertrek is going to be less likely to smooth out flat when you fasten foam over it if you've ever seen the tyvek products, you know they are essentially "crinkly" housewrap. Now, you didn't mention Cosella Dorken's membrane, which I believe is called Delta Dry. That stuff looks bulletproof, if not a bit excessive.
Note: sorry for typos, I was replying to your question via my cell phone.
Justin, thanks for the insight. Yeah, the "bumpy" surface of the WeatherTrek looked most robust to my untrained eye, but I was wondering if anyone with more expertise thought otherwise. On other forums, I've read concern (grounded or groundless, I don't know) about the "wrinkles" in the DrainWrap being pinched by siding being installed directly over it. Then again, putting foam on top would seem to be more forgiving, less likely to compress it.
Yeah, Delta Dry would be overkill, I think, for my purposes. Plus, I would imagine the larger gap would have more effect on the insulating performance of the foam insulation.
Any thoughts on the performance of the "groovy" RainDrop? If I Google it, the second hit is a DuPont-published hit piece explaining how terrible a product it is (according to DuPont, it won't drain and won't dry, but leaks water and air like a sieve).
Ian,
I don't have any experience working with RainDrop, but its non-perforated and has a decent perm rating, and has positive channels that won't easily be compressed when the foam is fastened tight to the OSB. It's vertical channels, I'm sure, will perform their duty for drainage, but I like the idea of the lateral ventilation that is built-in to the basketball-like texture of WeatherTrek. But this is personal opinion, and I'm sure that the Pactiv product performs adequately for the purpose you have in mind, especially since you are only looking to create a break behind the foam.
Thanks Justin, I appreciate it.
OSB should not be used if there is any concern for keeping it dry. Step up to plywood, or even pressure treated plywood, or even a commercial product that is less sensitive to moisture and rot.
AJ, I'm pondering upgrading to plywood, partially because it's more robust to moisture and partially because I just have more affection for it (so don't think I'm being flippant), but the WRB's job is to protect the sheathing from whatever moisture makes its way past the siding, rainscreen gap, and foam. Although not perfect, it seems pretty good, and I don't want to make the perfect the enemy of the good here.
Plus, shear value is a big concern (west coast), and I think OSB has a higher shear strength than plywood, although they are considered equivalent by code. As for other products, do you know of any that have the shear value of OSB and plywood?
Shear is an engineering question. Plans submitted for permits is where shear walls are to be detailed by those in that business not on a website casually discussed. Plywood certainly could and is spec'ed.
Any thoughts on Fortifiber's Hydro Tex?