In theory vapor accumulation is only really problematic in the overhead plenum spaces. In actual practice (setting aside acute water ingress) 100% of the time moisture problems start in the crawl space and then spread to the plenum.
Yes absolutely it is possible to design complex interlocking systems that at least in theory both provide high efficiency sealed construction and control moisture. In practice the complexity of these systems is sufficient that even top-end contractors frequently run into issues that lead to full blown abatement projects. There is also the minor issue of what happens if all of these systems aren't subjected to aggressive inspection regimes and/or a structure goes a significant amount of time unoccupied. The one thing all of these super high-efficiency sealed systems have in common is they quite literally tear themselves apart if neglected or the power gets turned off for any meaningful amount of time.
The statement "If structures don't dry they rot" is absolutely true, but only in the context of traditional lumber products that are comparatively resistant to rot in the first place and are capable of weathering swell/shrink cycles without falling apart. Highly engineered products degrade aggressively just by getting damp in the first place as swelling wood fibers break down bonds with the adhesive that's holding the material together.
I absolutely stand by my original statement that OSB shouldn't be code-compliant and with the exception of shitty flat-pack furniture has no business anywhere in a home.
> In theory vapor accumulation is only really problematic in the overhead plenum spaces. In actual practice (setting aside acute water ingress) 100% of the time moisture problems start in the crawl space and then spread to the plenum.
Which is a good argument for conditioned crawl spaces.
* https://www.buildingscience.com/documents/bareports/ba-0401-...
Shit is wack yo. Perfectly usable houses are remodeled all the time.
I hate OSB so much. And it no longer is that much cheaper than plywood, which still can die in water but at least doesn't die immediately.
* https://www.greenhomeguide.com/askapro/question/i-m-concerne...
* https://greenhomeguide.com/askapro/question/we-have-osb-that...
Unless you're using planks for siding and your flooring, you're going to have to use some kind of glued product product. Further your OSB is generally behind your drywall (sheet rock, gypsum) which can act as an air barrier.
Ideally you should have an HRV/ERV that exchanges the air in your dwelling constantly.
OSB is a fine air barrier, and most water vapour volume happens through air leaks. Vapour diffusion tends to be a smaller percentage:
* https://www.youtube.com/watch?v=FXXgjvOJcYI
The main place that vapour concentration really becomes a problem is at the highest point of the house (e.g., ridge):
* https://www.buildingscience.com/documents/building-science-i...
The main point is to not have your condensing surface on the inside of your structure:
* https://www.buildingscience.com/documents/insights/bsi-001-t...
Which is why so many jurisdictions are encouraging / mandating external insulation. When the sheathing is the coldest surface, of course there's going to be condensation, but if it's the same temperature as the inside air how would moisture accumulate.
> If structures don't breathe they rot.
If structures don't dry they rot. There are plenty of of <1.0 ACH@50 structures that do not "breathe" that have no moisture/rot issues because they take care of water mechanically, e.g., ERV/HRV and (whole house) dehumidifiers.
* https://www.youtube.com/watch?v=CIcrXut_EFA