cantilever airseal

[@jimmeh213]

Need more simple explanations like this. They're really helpful for small DIY renovations.

[@ProTradeCraft]

Glad it helps.

[@kylemacht]

You need to be careful to not have vapor impermeable insulation on either side of the batt insulation. You don't want to trap moisture in there. In this scenario, it should be able to dry through the rim. I would recommend skipping the interior rigid insulation against the floor.

[@ProTradeCraft]

Take it up with Steve Baczek; it is his detail. He is a pretty smart guy (but don't tell him I said that).

[@kylemacht]

@@ProTradeCraft Hahaha, nice. Steve knows what he is doing, but he also knows we can't make a vapor-closed assembly on each side unless it is a vapor-closed insulation. So depending on the materials chosen, this either works or doesn't. If the overhang is short enough, which it looks like it is, it can dry out to the interior of the floor structure and not be anything to worry about.

[@helmanfrow]

Yes, wondering this, myself. Why not treat it like a section of horizontal wall?

[@ProTradeCraft]

see answer in other Q

[@SlickGipsy]

Love this

[@helmanfrow]

Fun! What do we do after breakfast?

[@ProTradeCraft]

LUNCH!

[@dosadoodle]

The foam sandwich might seal in moisture that gets in the area. Unless the joists and blocking are themselves not a solid air barrier, in which case all that foam patchwork in each cavity and spray foam gunning isn't really doing any good. More generally, why not treat that area like a horizontal variant of a wall? . Insulate it like a wall, e.g. with batts . Sheath the bottom-side . Tape the seams, including any corner connections to wall sheathing, with a good flashing tape like ZIP. . Seal the sheathing / foundation connection however the sheathing/foundation is being sealed elsewhere, e.g. Siga Fentrim tape is a good option as it sticks very well to concrete.

[@ProTradeCraft]

I mean, your description is basically the same as what is drawn, except for the upper layer of foam, which is higher R value than fiberglass batts. You've got a potentially very clod floor here that needs all the insulation it can get. If you seal the bottom layer well, you should be able to keep moisture out. If moisture gets into the cavity, the condensing surface will be somewhere in the middle of the top foam layer, so, no condensation. Ask Steve Baczek for details, the drawing scomes from him, and as I said above, don't tell him I said he is smart.

[@dosadoodle]

@@ProTradeCraft Again, a foam sandwich looks risky. It's not a condensation concern in many climate zones, but that could be a concern here in MN (45%+ of insulation is ideally outboard of the vapor barrier to avoid condensation issues). If / when liquid water gets in, it cannot dry out, because it is a vapor barrier sandwich. Remove the upper layer of foam, at a trivial cost to R-value, and that will create a more resilient design to allow drying to the interior of that cavity. Better R-value doesn't help on bills or energy use if the entire floor has to be torn out and repaired in 10-20 years because of a small leak that develops in that area. I don't know what circumstances Steve suggested that design, but Steve also advocates for the use of large overhangs and rain screens while also designing for the specific circumstances of a build (e.g. climate zone). Without those details, I'm skeptical that this is a design that should be broadly recommended without mentioning those details. (But if Steve does in fact say this design is fine for broad use, then I'd yield to his opinion.)