Originally Posted by nealtw
Here we would be required to cut and fit solid blocking in the rim joist area and then solid blocking between the studs at the floor level. Rim blocks for earth quakes so they don't lay over and stud bay blocks for firestopping. We usually see bat insulation under the floor, no vapour barrier as the plywood is a solid surface and the other side wants to breath. They often have chicken wire to hold it up and keep critters out.
We also see solid foam cut to pressure fit and sealed with some special glue or caulking, that might work for you but is would want to be installed so it is in contact with the plywood when your done. tricky but not impossible I guess. Thoughts??
The main thing that keeps the joist stiff and not able to rack or topple is that they are connected to the wall studs coming down on the side of each joist but yes there is also solid blocking stiffing on both sides in the center of each span. there also is crossblocking (looks like a wall plate but not one piece) at floor level of the wall studs. As much as i researched this was a popular way to build homes in the early 1900's. A rim joist seems a better idea to me though as it makes wall studs more open to the elements to rot over years.
From what the spray foam guy and a couple contractors told me so far the best bet is to insulate the perimeter (aka rim joist area) with foam board and seal with spray foam. I like this idea but still wanted to get other opinions on it. I like your idea with doing between the joists with rigid foam as well . Doing both should help a lot. I have seen a video where they nailed furring strips halfway up the joists so that the rigid insulation sits flush with the top of the joists.Looked like a nice trick.