Progress, page 107
Nothing but a long 12 inch diameter hole in the concrete all the way down to the damper.
Once I got far enough to be directly under the roof opening, the rest of the chimney could be
commercial insulated sections. These are DuraVent units made by Simpson, and I needed four
3 foot sections (12 feet total) to reach the rest of the way through the roof. Here you can see the
base plate mounted to the concrete with anchor bolts and another rock wool gasket. I purposely
did NOT fasten the four sections together (or to the base plate) with sheet metal screws as
recommended by the manufacturer. They have a nice interlock mechanism between sections
and their weight alone was easily great enough to hold them securely in place, and I wanted to
retain the possibility to lift them out from the top should they ever need to be replaced.