Any case studies on moisture-sensitive exterior insulation failures?
These two clips from FHB and BS and Beer videos sparked some thoughts: https://youtu.be/tU9ciWUfM0A?t=4752
https://youtu.be/XfiRYQBU4_M?&t=1974
In the BS and Beer clip, Christine Williamson talks about avoiding exterior cellulose.
In the FHB clip, she is talking about stucco applied directly over wood fiberboard insulation and how she feels uneasy about it. This is not the same thing as a rainscreen gap and cladding over wood fiberboard insulation, but it got me thinking anyways.
EDIT: Straub also discusses similar concerns:
https://youtu.be/t4E1LkgYc9Q?list=PLeFMmszk7NskUQZUztUxmnRODXLXlqh1I&t=750 (keep watching through 15:05)
Foam isn’t moisture sensitive, which is great, but it has its own considerations for climate change and environmental impact, and some of it has an annoying habit of shedding particles everywhere when cut or emitting fumes when cut with a hot knife.
Mineral wool isn’t moisture sensitive, but has a high embodied carbon cost, the thickness is limited by its relatively lower rigidity, and it’s not the most pleasant to work with.
It seems like for these reasons and others, many assemblies seen in recent media are examples of using moisture-sensitive insulation like I-joist bays filled with dense packed cellulose or wood fiber insulation.
I assume in most of these assemblies the water control membrane is going outboard of the cellulose or the wood fiberboard insulation. Is there a second water control membrane on the sheathing inboard of the insulation?
I’m also wondering–have we seen any case studies or field experiments where moisture-sensitive exterior insulation has been subjected to repeated wetting? E.g. a tree falls on a house, and it takes some time to get a contractor lined up to fix it because it happened during a hurricane and they’re all booked out, and in the meantime, it’s getting rained on through a torn water control layer, etc.
In principle if your water control membrane is vapor permeable and well-detailed, this wouldn’t be a problem, because any incidental moisture can still dry out.
But has anyone tested to see what happens if soggy exterior insulation sits for a prolonged period of time in direct contact with the sheathing (with a water control membrane applied to the sheathing or not)?
It’s said that cellulose and wood fiberboard insulation can take on a lot of water with no issues because it can distribute it readily throughout its mass, and if applied in the proper assembly, it will also eventually dry out.
Is this similar to something like stucco, which can also absorb water, and will also eventually dry out? If it is, should moisture-sensitive exterior insulation be treated in a similar manner to stucco when it comes to the relationship with the sheathing? And if so, should a gap/capillary break be left between this insulation and the sheathing?
I’m sure someone has thought of all these things, I just haven’t seen them communicated directly in any media.
For what it’s worth, I’m definitely in favor of more climate change friendly approaches.
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There are wood fibre panels that are treated to be water resistant. You will see that there are many different products available in wood fibre insulation. You want to choose the appropriate ones to build the best assembly.
Take a look at this particular panel. The specs say
"• Superior moisture resistance due to hydrophobic treatment"
https://foursevenfive.ca/content/product/thermal_insulation/multitherm/spec_sheet_multitherm.pdf
If you want to see example of the use of wood fibre in an assembly(ies), you can get to see a number of them on the 475.com website. They insist on emailing a link to you but 475.com is a well regarded company.
Open this link and scroll to the bottom. There is a large button "Download smart enclosures".
https://foursevenfive.ca/blog/nature-does-it-best-gutex-wood-fiberboard-insulation/
Yes, these are the exact panels she's talking about in the video.
In another separate clip she also touches briefly on exterior cellulose:
https://youtu.be/XfiRYQBU4_M?&t=1974
FWIW, Timber HP out of Maine also has rigid wood fiber panels that are treated to resist moisture. Not on the market yet, but their brand new mill is coming along nicely, with deliveries expected through 2023 at different times for each of their products. They claim the panels are water resistant enough to act as the WRB.
I haven't had the opportunity to tear apart any buildings with wood fiber exterior insulation, so no personal experience in that regard. But comparing to OSB sheathing, which is also treated to be water resistant, I have some concerns. I'd be far more comfortable installing the siding over a rainscreen to prevent water being stored in small pockets and to allow some drying. Short-term wetting should not be a problem with these materials, like from the tree you describe or simple rain wetting during construction. It's when these materials are kept wet for weeks, months, even whole years that they start to have problems.
Also, wood fiberboard is not an air barrier, so we need to add an air barrier (or two) to the wall system and that air barrier may just as well also serve as an additional WRB.
For pictures of existing damage, I looked around and the best I could find was this: https://inspectapedia.com/structure/Homasote_Roof_Insulation023-DLs.jpg
and this https://inspectapedia.com/structure/Fiberboard-Roof-Panels-200-Canada-JoshuaC.jpg
From this page: https://inspectapedia.com/structure/Fiberboard_Sheathing.php
The common denominator is that these products were installed on a roof. The second picture doesn't describe the specific product, but for the first, I believe Homasote is generally treated for water resistance, although it's not clear how it compares to something like Gutex.
I should have also addressed your question: "I’m also wondering–have we seen any case studies or field experiments where moisture-sensitive exterior insulation has been subjected to repeated wetting? E.g. a tree falls on a house, and it takes some time to get a contractor lined up to fix it because it happened during a hurricane and they’re all booked out, and in the meantime, it’s getting rained on through a torn water control layer, etc."
I don't know of a wall assembly that would do well in such a situation. If this is your place and you an able bodied individual, you need to be ready and willing to jump in immediately to get the tree off the house and tarps on to cover the wall/roof.
I have read about people in my area affected by an tornado where there was totally unsual degree of damage to a large number of houses. They then complained to a news network that work was taking too long and that their house was ruined (weeks/months later) because the insurance contractor had not sealed the house properly... and my thought was "why did this couple sit by and just watch their investment go down the drain?" For people with physical and health limitations, I would spend time thinking of how such a situation could be managed and make solid plans.
If this happened to a wall with mineral wool or rigid foam, the insulation would be fine. If it happened to a cellulose bay, not so much.
Another case would be hot, humid air reaching the exterior surface of the sheathing/water control layer. If that layer is quite cold because of air conditioning, water will condense on it. With mineral wool or rigid foam, this doesn't matter--these materials are not moisture sensitive.
With cellulose, it's a different story.
andyfrog,
I think it perhaps depends on how much bulk water intrusion there is. With small leaks cellulose might perform better than hydrophobic alternatives, as it can redistribute and dilute moisture. At a certain point maybe that logic flips?
A bit unrelated to Christine's concerns, but if the wall assembly doesn't need the moisture buffering cellulose brings, I much prefer using mineral wool, or even high density FG batts. No worries about settling, easy to remove, reinstall or replace, and DIY friendly.
Yes, in principle I'm not opposed to cellulose. I'm mostly just surprised there's apparently not a lot of research on it.
After searching extensively, this is all I've found, and it does look extremely promising :
http://cchrc.org/media/SafeAffordableRetrofits.pdf
http://cchrc.org/media/SEAR_Report.pdf
http://cchrc.org/media/CelluloseSnapshotFinal.pdf
It's noted in some of the reports that builders they interviewed regarding the various enclosures expressed concerns about bulk water intrusion into exterior cellulose.
Some interesting questions that come to mind are:
1) what happens when soggy cellulose remains in direct contact with a water control membrane applied on top of sheathing? e.g. a bulk water leak that remains undetected
2) what happens if the water control membrane that wraps the cellulose is exposed to excessive UV, heat, cold, surfactants, pine needles, etc, and then exposed to incidental bulk water? There was a guy on youtube who had Mento on his roof sheathing during construction, and before he could get his roof on, falling pine needles dotted thousands of tiny holes in it that ended up leaking.
I am definitely in the camp of hoping that exterior cellulose is robust, especially because from a hygrothermal perspective, even a marginal, generally-considered-unsafe thickness of 3.5" in the extreme cold of Alaska appears to outperform even mineral wool.
It just seems strange that there is momentum for its use without holistic data analysis.
I suppose it's the dissonance between things like "bury the control layers in a protected location" and the general enthusiasm for exterior cellulose that is discomfiting.
Straub also discusses similar concerns:
https://youtu.be/t4E1LkgYc9Q?list=PLeFMmszk7NskUQZUztUxmnRODXLXlqh1I&t=750 (keep watching through 15:05)