Is it allowed? I have conflicting plumbers. I have a home where CSST goes from inside the home near a furnace, through a solid wood sill plate, under an outside deck, and on to a BBQ grill. I realize that connecters cannot go through walls, but what about CSST? Engineers here will not commit, but say the “pipe meets code”. They will not say that it is allowed through ledgers and sills, from the inside of the home to outside. Home was built in 2005, and no changes have been made to the home since.