
OK, so the third floor is as solid as a rock. The FIRST floor is also solid and sturdy. So what the hell happened to the second floor? Did the builders just get lazy?
This is an image of the joists under the third floor, the stable one. The floor I'm standing on to take the picture bounces as I walk across it, enough to make a Yankee seasick.
And of course, I have the 'heights' thing, so I'm constantly thinking I'm going to fall through and kill myself, at which point I know my husband will immediately make plans for building a large, (nay, massive) brick and stone outside grill monstrosity at the rear of the house, and I just can't have that, now can I?
So we need to stabilize the second floor. All of the original criss-cross joist braces in the picture above, are oddly missing on the underside of the second floor. I think we'll just add in 2x8" blocking, staggered by 8-10", and then, since we're not planning on having wood floors on the second floor, we'll just overlay the whole floor with 3/4" plywood or OSB and screw it to the subfloor.
Update: We just bought a 90 degree drill attachment for the cordless drill to fit in between the roof joists, a 3/8" drill bit and a lot of 3/8" bolts to attach 2x8's to the sides of the joists for reinforcing (called "sistering"). The drill bit seems to work well in cutting through the joists, a lot easier than I was expecting, actually. I've heard stories about the old joists being close to petrified wood and going through a lot of drill bits.
The only thing I wish was that we had taller ladders. Those joists are way up there and a tricky balancing act on two ladders holding up a 2x8. Something you may want to consider.