When you can’t put it off any longer and are finally forced to have the discussion, start by asking if the house style guide is just a style guide or if it’s more of a training document. If it’s a style guide, then maybe it doesn’t make sense to repeat a bunch of rules that are already found in Chicago, but if it’s a training document, then maybe it makes sense to put all of those common Chicago rules in there to provide an easy reference for the interns and help them get up to speed faster.