Subfloor Gaps

[Pappynoodle]

Hello everybody. This is my first post but I've read countless hours of information and super grateful for this forum. My tile installs look better than 90% of contractors I've seen in my area and a huge thanks is owed to this forum. Now for my question, I'd appreciate any insight or opinions on. I recently purchased a 2,100sf home and the entire crawlspace foundation is crap. I'm replacing ALL joists, piers, beams, subfloor, EVERYTHING. I've ripped out the subflooring (2 layers of varying 3/4) and now I'm in the planning stage for rebuilding.

One of the biggest issues I keep coming to is getting the 3/4 Advantech I intend to use, underneath the load bearing wall I'm replacing and all of the partition walls. If I use blocking and am able to butt the subfloor against the bottom plate of most walls, will the gaps in certain areas become an issue with air/moisture? I've used spray foam in the past when I've done repairs on subfloors that were 3/4 planks ran on a 45. I would spray foam the gaps around the perimeter of the room and come back with my oscillating tool to cut flush. Is the spray foam enough to cut down on air/moisture or did it just make me feel better?

When I say I've racked my brain on this, it's an understatement. I've got drawings and ideas everywhere. I've considered a system I designed that would allow me to rebuild the pier, beam, and load bearing wall in 8ft increments. I considered placing a piece of subfloor down under the loadbearing wall as I build it back but getting it square enough to meet the other sheets later and having my temp wall back far enough for a 4ft sheet seems a bit daunting. Even if I was able to perform that, the thought of the numerous partition walls makes me a bit overwhelmed. I'd considered cutting a small section(1-2ft) off the bottom of the partition walls and then putting in new bottom framing plate and sistering back to original studs after I had slid the new subfloor in. That also sounds like a TON of work and most of the walls are rough framing so getting a 1.5x3.5" stud to work with new drywall may not be a possibility. Plus if I'm sliding in a 4x8 sheet on the joists, getting subfloor adhesive on the joists would be tremendously difficult if possible at all.

Apologies if that's too much but I've got a lot going on lol. Long story short... can I butt my subfloor to bottom plate of walls instead of going underneath and caulk and/or spray foam the gaps that would surely present themselves in that process? Thanks in advance!

 

[wwhitney]

Generally every edge of each subfloor panel is supported either by a framing member or by T&G into an adjoining panel.

So if you are replacing the subfloor within a room without replacing the subfloor under the walls, you'd typically take some measure to support the edge of the new subfloor where it is butting into the existing subfloor under the walls. E.g. if the wall is running perpendicular to the joists, install flat-wise 2x4 blocking half under the subfloor under the wall, so it can catch the new subfloor.

Or just install a strip of 3/4" sheet material underneath the joint that is secured to the subfloor on each side of the joint but is otherwise floating. E.g., put it in place before the new subfloor, screwing it to the subfloor under the wall from below, and then screwing the new subfloor to it from above.

Cheers, Wayne