I have to admit that I don’t really know what this is. The other day I did an inspection and found there was an opening, about 6 inches, around the chimney at the attic floor. I thought there should be some sort of flashing around the opening but wasn’t sure. It is a lined, brick chimney, and the home was built in 1955.
If anyone can offer me any help with this I would appreciate it.
The only purpose I can think of was that the framers wanted to give the brick mason plenty of clearance to bring the masonry up through the floor and attic.
If the fireplace is in good condition then I would simply deal with the air filtration / draft
issue. You really don’t want to frame up tight to the chimney.
As to any flashing, just ensure that same is flashed properly as it penetrates the roof.
Framing shouldn’t be closer that 2" to a masonry chimney but it could use fire stop.