OK, I gotta tell you, we were thinking about firebreaks completely differently than the way we were supposed to. Jeff Bechtold from NKAPC gave us an early inspection this morning (A very nice guy, btw- lot of information and very helpful) and pointed out a lot of ways we need to make new fire breaks in our walls. There are LOTS of them needed.
The good news is that we can fix all of them with rockwool (mineral wool) and 1/2" OSB in hopefully under a day.
I've got a lot of pictures to take of the right way and wrong way to make a firebreak, which should be helpful to anyone going through this process.
Jeff kept repeating that "the horizontal and the vertical [spaces] can't communicate." Meaning that if you have a space going from a wall to the ceiling (the way a fire would normally travel) if the horizontal space meets with the vertical anywhere, that's bad.
I put it in different terms.
You're a mouse. You're climbing up a space in the framing (or wall) and if you can get through to the floor above, so can a fire.
You have to think like a mouse.
Unfortuantely this means we could have saved ourselves a lot of time and effort building this aspect into the framing while we were doing it, but now that bthe framing is up, we're going to be making a lot of small OSB cuts to fill gaps in the framing and we're off to buy 2 bales/packages of rockwool.
*Jeff mentioned that if we got an old butcher knife to cut the rockwool it would be easier to get into small pieces that we could then use a shim to poke into the small mouse-sized spaces that need filling.
As to the firebreak spray foam: rockwool is cheaper.
Oh, yeah, and he said the third floor attic/storage wall was just fine. :-)
OK, we're off to the insulation store!! (Jensen's Insulation in Erlanger.)