hi 1320ms - this is my two cents
my first choice would be to rent a toe-kick saw to cut nearly flush with the bottom plate of the exterior wall. second choice would be to carefully use a sawzall with a long blade. my third choice would be to use a regular circular saw to cut within 2"-3" of the bottom plate.Where the water damaged areas are up against the exterior walls, and the framing sits on top of the subflooring, what is the best way to go about replacing the flooring?
yes, butt the new subfloor up to the bottom plate, but leave a gap of about 1/8" - 1/4" for expansion.so do I just cut it at the bottom plate and lay new subfloor down?
you'll have to put blocking under the edges of all your new subfloor, and nail (or preferably glue and screw) the new subfloor into it.
where the walls are perpendicular to your floor joists, you can install full-height blocking (same height as your floor joists) or 2x4's laid flat to fit tightly in between the floor joists.
where the walls are parallel to the floor joists, i'd install full-height blocking instead of the 2x4's laid flat. install them every 16". make sure the edges of the new subfloor panels fall onto the blocking.
i don't think it's necessary for the blocking to provide support to the bottom plate of the existing walls. obviously, when you install blocking when the walls are parallel to the joists, it should fit the entire width of the joist bay - so it will support the bottom plate. but when walls are perpendicular, i wouldn't really worry about trying to slide half of the blocking under the existing bottom plate/subfloor.
i also don't think it's necessary to attach any of the blocking to the existing walls...i.e. you don't need to screw upwards through the blocking into the
bottom plate (or through the bottom plate into the blocking). but if you have access, it might be a good idea.
no, not that i'm aware of.Does this in any way alter the structural integrity of the wall if I'm cutting the subfloor at the bottom plate?
if time and budget allows, yes. or 3/4" OSB. i'd rather go with 3/4" OSB than 1/2" plywood, if money's a factor. if plywood, use B-C rating. either case, glue and screw it down.should I step up to 3/4" plywood and replace all of the subfloor throughout the entire house?
no, i wouldn't feel comfortable with particle board as the only subfloor.Should I just replace the rotting particle board with more 21/32" particle board?
my opinion, no. replace it all.Or should I replace the rotten sections with 21/32 plywood leaving a mix of particle board and plywood as the subflooring?
yesWhere the interior walls sit ontop of the existing subfloor, do I again just cut at the sole plate of the wall?
follow same blocking spacing and recommendations as above.If I replace all of the subfloor, following this method, all of the walls would be sitting on a piece of 21/32 particle board that is cut at the sole plates on all sides, again, would this alter structural integrity of the house?
if the interior wall is perpendicular to the floor joists, it's already well supported. just make sure to block in the joist bay where the bottom plate ends, if it doesn't end right on a joist.
if it's parallel to the joists, when you install blocking every 16", i'd try to screw up/down through the blocking into the bottom plate.
hope this helps