DRIVING MYSELF INSANE ON TYPE OF INSULATION PLZ HELP
I am building a new house here in NW kansas (Zone 5a). My builder wants to do flash and batt Hybrid insulation on the 2×6 exterior walls. (Huntsman HFO PRO 1″ closed cell Greenguard gold certified) Followed by blown fiberglass to fill the rest of the cavity. And im having a really hard time deciding if I should do the foam or just do the fiberglas BIBS only. So many pros & cons online, but seem more cons so im leaning towards not doing it. But my builder thinks im a little crazy. My exterior sheathing is Zip system (Seams zip taped and nail holes zip liquid flashed), my siding is LP board & batten. My biggest concerns are MOLD and of course off gas/vocs but the hunstamsn XPS PRO is greenguard gold. We will have a RenewAire EVPremiumM ERV regardless of the insulation route we go.
I have a full finished basement he wants to do 1″ of spray foam on those walls, which im hesitant on as well, if I ever have a basement leak I have to somehow scrap all the foam off. I would rather just do batts down there only fiberglass or rockwool. The exterior of the basement walls is sealed but not insulated.
Rim joist 3″ of closed cell spray foam (not much option here)
And as far as the attic R38 blown fiberglass
Anyway any thoughts on the insulation for the exterior walls & the basement walls?
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You can't use closed-cell foam with ZIP. Moisture could build up between the two layers, and won't have a vapor-permeable path to escape. ZIP is essentially vapor-closed, so your assembly has to be able to dry to the inside.
On the exterior, look into a rainscreen so the siding isn't intimate with the WRB. That will help the assembly shed water, in case it gets behind. While LP normally says it isn't needed, it's a good practice to help materials last longer.
If you're building a tight envelope via ZIP sheathing, you should aim to eliminate spray foam in all but the most impossible of locations where batt or even blown-in insulation can't reach.
From what you describe, I would personally go with Hempwool batts in the wall cavity, and then use ZIP-R to add a bit of continuous insulation across the framing. For the basement, there are definitely rigid foam board alternatives to spray foam. I always prefer plant-based items where available, but I can't say off the top of my head if there are good wood-fiber boards that can mount directly to masonry exterior walls. For the attic, go with blown-in cellulose vs. fiberglass. Comparable cost and performance, but cellulose is a recycled material and potentially less troublesome if you have to do any maintenance.
In short, stay away from spray foam. It looks cool on HGTV, but it can become very problematic in practice, to say nothing of the high carbon footprint from polyurethane.
Scott,
I don't see the point of using the foam here either, but not for the reason you cite. Zip is not a vapour-barrier. It has a perm rating of between 2 and 3, which is about the same as both plywood and OSB (until plywood becomes wet), so it can dry fine. Walls with Zip sheathing are usually designed to dry to the outside.
When I looked up the perm eating of zip it shows 12-16
Josh,
The protective surface is 12-16 perms, the total Zip panel is 2-3.
That's the perm rating of the green or reddish brown exterior coating. The OSB is around .05-1 perm when dry and as Malcolm said, 2-3 perms when damp, which is when it needs to dry. So the most limiting factor is the OSB but it still allows for drying.
I have no problems with adding 1" of closed cell foam on the interior, which is around 1.2 perms at 1" and also allows for drying.
Looks like we're both right — the foam part of ZIP-R has a perm rating less than 1, according to Huber. The panel itself has 12-16. https://www.huberwood.com/uploads/documents/technical/Product-Data-Sheet-Wall-R-sheathing-ZIP-System.pdf
Scott,
See Michael's post #6 above.
The original question did not appear to include Zip-R, the type with foam, but a few years ago I heard directly from the technical director of Atlas, by way of a friend, that their fiber-faced polyiso is 1.0-1.5 perms. That's per inch, and accurate for their R-6 product. Their R-9 product would be about 0.75-1.0 perms and their R-12 product would be about 0.5-0.75 perms. As far as I know, Atlas still provides their polyiso but that might have changed.
Haven’t heard that yet in the zip not being able too dry too the outside. If that’s really true I’m sure glad I asked. It shows a perm rating of 12-16.
I looked into rain screen but ended up not doing it, and it’s half done now. Ugh. I agree water in the back side of LP which is essentially bare OSB won’t last very long.
I can’t use zip R. Too late.
So what would you do for the rim joists then? My floor trusses or open web. Seems like my only option is closed cell spray foam
That's for the coating, not the OSB.
Scott,
To get back to your original question:
I don't see any advantage to the spray foam in your wall cavities. Just use BIBs or batts.
In the basement you need to use impermeable insulation against the concrete to stop condensation. I would use foam board, not spray foam, and would do the same on the rim-joists.
https://www.greenbuildingadvisor.com/article/three-ways-to-insulate-a-basement-wall
https://www.greenbuildingadvisor.com/article/insulating-rim-joists
What is your goal with this house?
To my ear R38 attic sounds like code minimum build.
The way I see flash and bat walls they were a pre zip way to get more air tightness from a building by builders unwilling to put any effort into air sealing and pretty much dinosaurs today for new construction.
If you put damps sprayed cellulose in the 2x6 wall you get about R20 that pairs nicely with the R38 attic.
If you want the next step add an inch of exterior foam and bump the attic up to R60.
Note I see any large areas of spray foam in a building plan as a red flag as a lazy work preposed by someone with zero regard for your budget.
Please edit the title without the caps lock on
Walta
Former spray foam contractor here ...
You wrote:
"My biggest concerns are MOLD"
I think you are going to have to specifically spell out exactly what your concern is ...
IMHO I think your builder is probably also concerned with controlling the first condensing surface (where moisture forms) by wanting to use a "flash & batt hybrid"
Presumably you are going to also control bulk moisture from the outside of your foundation wall - many people use a roxul type of product (similar to a "rainscreen" above grade) that allows bulk moisture to drain to the bottom of the wall and then captured by a "french drain" also using a belt & suspenders spray or roll on a flexible membrane
See "Warm-N-Dri & Tuff-N-Dri" products as examples (I used these on my own house)