Your videos are great! I have one concern though with the foam assemblies that you show: You are running the foam continuously from behind the wall up into the ceiling cavity, without the required fire blocking to isolate the wall from the ceiling. The solution for this that I'm planning to use in my own basement is a horizontal strip of plywood across the top plate and up against the concrete wall. A bead of fire-caulk on the edge of the plywood seals any gaps and prevents moisture transfer from the concrete. And, using fire-treated plywood would give extra fire protection and the borate in the treated plywood gives some extra resistance to rot.
Thanks so much for pointing this out. You can actually use mineral wool batts as a fireblocking material per IRC 718.2.1., though now I just realized it wasn't on the spray foam drawing. Some spray foams also are fire rated, but I'm not sure if they can satisfy that requirement... Anyways, I'm pinning this comment because this is important. Cheers!
I'm rapidly coming to the conclusion that both expanded and extruded polystyrene foams are a really bad choice for the vast majority of wall and roof/ceiling assemblies, and it's due to the fact that they are almost completely vapor impermeable, and thus, when temperatures invert at certain times of the year or under extreme conditions (much of the US climate zones), promotes condensation on one side that does not easily dry. It's like trying to put up a vapor barrier in the wall assembly, which is fine, so long as there is a pretty much constant source of heat/vapor pressure from the correct direction. I'm ditching the stuff and attempting to utilize mineral wool batts and boards, along with some cellular glass in certain locations whenever possible. I'd be happy to hear your thoughts. Thanks for these vids, regardless, as us architects are always trying to improve the robustness in our buildings.
My thought, based on the consensus from every other building science site that I've visited, is that this would be risky, because there would be very little drying possible on the below-grade, waterproofed concrete wall side. This video is proposing what you suggest as an option, but only in conjunction with a tightly sealed smart vapor barrier. However, I haven't encountered any other site willing to propose this. I'd also think that the stability of the the ground temperature would eliminate the inversion concern -- the ground is always colder than inside. Above grade where there is inversion, the wood walls can dry to both sides.
I hear about both approaches and each camp seems to be pretty firm that their way is the better way. As a homeowner this is infuriating. Shouldn't there be some solid evidence/science to prove that one of the ways is the better way, or describe which method is best for different situations? I would like to insulate my rim joists using 2 layers of rockwool comfortboard, which you seem to recommend as well. The concern I have is condensation on the inside during winter (heating dominant climate). It's like putting heavy drapes over windows. Wouldn't this just cause a ton of condensation to build up behind the insulation during the winter season?
Good presentation. You mentioned long-term off-gassing from ccsf and wondered where you got that information. There appears to be a ton of conflicting information about this topic, especially when the discussions revolve around faulty installation vs inherent danger of ccsf due to chemical composition.
Without releasing too many of the details, we had foam core samples taken to a couple of independent 3rd party labs for testing after my client was experiencing some health issues. Foam comes back loaded with chemicals that presumably should have offgassed months prior. They sent the results of the foam samples to the manufacturer who responded with a formal attorney's letter that the lab results were normal... This is one anecdote, but many of my other building science contacts have run into similar issues. An acquaintance of mine Bob Kelly who developed the WickRight has seen a bunch of issues with spray foam, and met one of the guys who helped to pioneer CCSPF at Building Science Summer Camp and had some pretty interesting discussions. Definitely reach out to him if you're curious.
What solutions can you recommend in older homes that might not have the sill gasket and where the rim joist comes in direct contact with the concrete wall? Is spray foam still recommended in that scenario? It is a condo so I also don’t have access to the exterior to seal transitions
Thanks, this is just the right information I needed. I want add insulation to the rim joist area of my home and I'm going to use the second method you mentioned using xps foam. I wouldn't be doing anything on the exterior for now. For air sealing the cinder block the only tape I can find at my local hardware store that is wide enough for my application is vycor plus Self-Adhered Window and Door Flashing tape. Do you think this product would be acceptable in this application? Than you.
For drawing 3, would a vapor barrier be need if there was a dedicated dehumidifier in teh crawl? Also, what are you thoughts on a 4 foot deep crawl, with 2 layers of 2 inch stagger polyiso and a 10 or 15ml vapor barrier encapsulating the entire crawl. no cement slab, just a floor of poly with the plastic on top up to the sill plate. thanks
