Twin home, built 1987. In the unfinished attic the last joist does not fully touch the firewall and there is a sizeable gap, 1-2 inches. There is some splatter from mortar along it. I suppose this extends all the way down the length of my side of the home? Should I be gap filling this and would I need to use the "firewall" rated stuff or anything? Wish I had a pic but there are bats in the attic and I have to wait till their eviction next month. When I was cutting a hole in the drywall on the first floor near the floor to route some cables from the basement, I didn't notice there being much space behind the stud... so maybe the home has settled and that's the result in the attic?
Edit - Finally evicting bats and got the pics.