For future reference we typically use a channel to bolt to the side of
the chimney. You can easily find them with flanges in excess of the
required 2". You can use them to attach a nailer, or simply lay them
flat with the web up and use it as a seat. Satisfies the code, but
provides a thermal bridge. Use at your discretion. I have never been
questioned about it though (See E.I.T. below :) )
Jake Watson, E.I.T.
Salt Lake City, UT