Hi guys, first of all, thanks for all the suggestions and advice!
Now to clarify some things;
1) The joists are not toe nailed to a rim joist, they are sitting on a 2x6 (I think) sill plate, which is sitting on the foundation. There is blocking between the joists at the sill plate, so that end is firmly supported, I measured at least 6 inches sitting on the sill.
2) The the two joists that are above the posts are butted up tight against the beam, they sit squarely on it (joists 2 and 6)
3) joists 1, 3, and 5 have about a 1/8" gap to the beam, joist 4 is almost 1/4"
4) I measured the joists they are all 7 1/2" to 7 9/16" (hard to measure!)
5) The aquarium will sit perpendicular to the joists, so it's supported by the multiple joists, not just one or two
6) The gap is NOT between the post and the beam, as was pointed out. Sorry, this wasn't very clear in the first post. I had a heck of a time putting that beam up there by myself, it required milk crates and scrap wood! Lifiting an 8 foot piece of 4x8 in a crawlspace by yourself is not easy!
7) I tool a look at the main house beam and I can see that there is a gap between joist 4 and the beam as well! Joist 4 also appears to be tight to the subfloor, the other joists SEEM a bit less tight.
8) I took a straight 2x4 (checked it with my handy dandy laser level) and shoved it around down there, the bottoms of the joists in question are NOT IN LINE. I can't get any straight edge to span more than 3 adjacent joists without a gap.
9) The sub floor is solid wood, I'm guessing at least 1/2"`thick. It's 3 1/4" wide planks. On top of this sits the hardwood floor which is 3/4" thick oak (According to the guy who refinished it years ago, so it's not quite a full 3/4" after sanding down) The subfloor planks run perpendicular to the joists and the hardwood floor runs parrallel to the joists on top of that.
10) The joists are a bit rough looking, meaning they are not like what you'd see at Home Depot, they hare not sanded smooth or anything, I don't know if that just means that they are just bumpy and that might be why some joists are butted up tighter against the subfloor?
11) The floor above is fairly flat, it's not sagging at all. I poured some water on it and it pools, rather than runs in any direction.
OK, thanks for reading all of that!
My conclusion is that maybe some of the joists are slightly crowned up, with the biggest gapped joist being the most crowned up towards the subfloor.
The bottom line though is that ... there are gaps for whatever reason.
Some possible solutions as presented in this thread;
- Crank up that post and force the low joists up
- shim with wood
- shim with metal
- index and notch the beam with appropriate sized notches, then fit the beam back and all joists will sit in the beam notches. This would mean that I would notch 1/8", 1/4", 1/8", 0, 1/8", 1/4" so that the top of the beam meets the largest gapped joist and the currently ungapped joists will sit in 1/4" notches.
I really don't want to force that low joist up (nor will I notch the joist!) because the lathe and plaster walls might just decide to show me what they think of forcing them out of where they have settled in the past 70 years.
Shimming is easiest, but it seems to raise the most red flags with you guys. Metal would be preferred over wood.
Notching seems like a good solution as it is similar to shimming but without the stigma of shimming. This requires the most work as I have to uninstall the beam, cut new posts and notch the beam. However, if this is the best solution, that's what I'll do.
Thanks for reading this long winded post! And thanks for your advice, tell me what you think!
Vince