Just one more…exterior Insulation moisture question for the archives
kate.h
| Posted in Green Products and Materials on
Hi GBAs,
I have truly read so many of these articles about insulation choices in the last 2 months but alas, here I am with a question about my own specific recipe of materials because it feels like every variable changes the game just a bit…
Climate Zone 5 in Western MA. We are builders and also the owners.
Wall assembly planned as follows from interior out:
drywall, 1.5″ service cavity, intello, 2×6 stud framed walls with TimberHP batts, 5/8″ plywood sheathing, Solitex mento 1000, 2″ rigid insulation (where the question lies), 3/4″ horizontal rainscreen battens with strips of some kind of venting materials behind them, vertical wood siding. Innie windows.
Our original plan was to use the TimberHP rigid boards for the continuous exterior layer but since they are not yet available and our budget is shrinking we are trying to reconsider options for this layer of the assembly. Price and environmental consciousness and avoiding moisture problems all feel important
. We are trying to figure out what is required as far as permeability or lack there of for the rigid insulation. Will it work to use 2″ of a recycled CGF polyiso (is this the same as when people refer to fiberglass faced?)? Does permeability of this layer matter if we have the Intello allowing things to dry to the inside? It seems we might have been smarter to go with a hydrogap type WRB instead of the Mento so that we could think less about moisture on the rigid insulation and create some drainage between those two layers, but we already have it so not trying to back track there. Is there any reason to consider Halo Exterra which seems middle of the road price-wise? And would we need to tape the seams of whatever foam we use or can that be avoided since the air and water barriers are covered elsewhere? Last scenario, if we can get a really good price on recycled paper-faced polyiso would it work to just wrap that in an additional WRB layer to protect it but still flash windows to the WRB at the sheathing?
. We are trying to figure out what is required as far as permeability or lack there of for the rigid insulation. Will it work to use 2″ of a recycled CGF polyiso (is this the same as when people refer to fiberglass faced?)? Does permeability of this layer matter if we have the Intello allowing things to dry to the inside? It seems we might have been smarter to go with a hydrogap type WRB instead of the Mento so that we could think less about moisture on the rigid insulation and create some drainage between those two layers, but we already have it so not trying to back track there. Is there any reason to consider Halo Exterra which seems middle of the road price-wise? And would we need to tape the seams of whatever foam we use or can that be avoided since the air and water barriers are covered elsewhere? Last scenario, if we can get a really good price on recycled paper-faced polyiso would it work to just wrap that in an additional WRB layer to protect it but still flash windows to the WRB at the sheathing?Thanks for any recommendations,
Kate and Dan
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Replies
Kate and Dan,
What about rigid mineral wool?
I do not know enough about anything to say yes or no, that will work or will not work. But I do know that rigid mineral wool is permeable.
Thanks for the thought. I think comfort board would work very well, it’s just so much more expensive than a recycled polyiso so we were trying to see if we could find an alternative.
I've used fiber face polyiso without issues on walls (including on my own home). It is one of the better rigid options as it is somewhat permeable.
At 2"thick over a 2x6 wall is sufficient for condensation control, the permeability doesn't really matter, but it also doesn't hurt.
Cost is right and being reclaimed means much lower environmental impact. About the only issue with it is some of the reclaimed stuff might have a bit of smell. Something to watch if you are doing a balcony.
P.S. 2" polyiso is enough for condensation control in zone 5. You can skip the intello. Doesn't hurt but also doesn't get you much if you can detail your sheathing as your main air barrier.
P.S.S I like to put the WRB over the foam and mount the window as outies. This simplifies all your flashing details as everything is in plane. The bucks can be simple 2x lumber ripped to 2" picture framing your rough opening.
Thanks for the reply. To clarify, is what you’ve used in the past the CGF polyiso and not what people refer to as “paper-faced”?
We’re already committed to the innie window plan so I’m trying to figure out if we can use this CGF polyiso over the wrb on the sheathing and avoid another layer of wrb over the rigid foam. And whether or not taping the foam is necessary in this scenario. Thanks so much for your insights…
Kate