is this bad ?

Welcome to the club! I have the same thing -- that's vintage 1950s era fireblock right there (at least in my part of the country).

In my house they used, bricks, rocks, and sand -- and covered it in each bay with a piece of wood to hold it all back. It makes it impossible to run any new wiring from the basement directly to the first floor as one normally would.

It also makes sealing the rim joist impossible. The best I can do is seal the blocking piece of wood. Thus, there is cold air leaking up from the rim joist to the outer wall baseboards on the first floor. If you haven't sealed your first floor baseboards, you probably have the same issue.

I have cast iron piping running up the some of the bays, and in my case, the bricks were either removed or are not present -- I imagine to not block the passage and allow the piping to be run. Unless your bricks are too hot to touch, I don't imagine there would be an issue there, but others can chime in on that regard.

I'd say it's a good thing that you're keeping the rim joist warm and above the dew point. That will keep moisture from condensing and causing rot problems. So long as it isn't hot enough to set wood on fire, I'd say this is fine, a good thing even.

i don't see this as being fire blocking. if the bricks were not there, there would still be no where for a flame to go. i think they are there as a part of the structure of the house, i see them serving no purpose. but i guess they did back then, whenever "then" was.

i did seal the rim joist. i caulked it when i was doing the siding.

i'm not heating all of these brick bays, only 3 of them. but the basement is normally not that cold, its 60ish right now. and not directly heated in any real way. and 3 sides of the house, the rim joists have 1" xps on them on the outside.

i would love to not have these bricks in there.
but i have removed a few bays of them = NOT A FUN PROJECT !!!

So you just sealed the rim joists on the three that you removed the blocking from? That's fine.

As for the others, you basically want to keep the joists behind the blocking above the dew point to avoid condensation. If your basement doesn't get that cold and there is OK air circulation this shouldn't be a problem.

Whatever you do, don't try to insulate the gap around the blocks. That will lower the temperature of the rim joist, and if you don't seal that area, humid air will condense there and lead to moisture issues.

Thunder Chicken said:

So you just sealed the rim joists on the three that you removed the blocking from? That's fine.

As for the others, you basically want to keep the joists behind the blocking above the dew point to avoid condensation. If your basement doesn't get that cold and there is OK air circulation this shouldn't be a problem.

Whatever you do, don't try to insulate the gap around the blocks. That will lower the temperature of the rim joist, and if you don't seal that area, humid air will condense there and lead to moisture issues.

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i sealed the rim joists on the 3 sides of the house that i put siding on, on the outside. the joists set pretty tight to the block, so a good brushing and caulk sealed em up tight. and, i ran the siding, 1" xps and house wrap down over the block just a little. i did not do the front side yet.

Yeah, that's fine because that will keep the interior surfaces of the joist warmer. I wouldn't do anything to close the rim joist bays on the inside.