I believe it should be 18 gauge steel with a minimum of 8 compliant nails on each side into the top plate. Am I missing something?
I don't think it's an oval flue and the insulation appears to be installed poorly not filling the wall cavity properly.
That insulation behind the duct doesn't look compressed at all.
Exception: When the entire side of the wall with the notch or cut is covered by wood structural panel sheathing.
Jar, Is that Advanced Code Group photo copyrighted?
I think all put my PJ's, get a coke and a piece of pizza and design a picture book, kinda like Upcode did!
"Pajama Pirates!"