Thanks, adriver! You are right about the pitch. It's only about half the pitch that shingle manufacturers recommend. I really appreciate that you pointed this out. I am going to have to add a Grace Ice and Water Shield underlayment (or the equivalent) on the roof sheathing, before laying down the tarpaper.
My shop next to the carport has Hardiboard lapped siding, which is a masonry product and quite resistant to rot. I have caulked all the Hardiboard overlaps thoroughly with DAP "Custom Flexible Patch" elastomeric patching compound, which is the caulk that Hardiboard recommends. I really like the Hardiboard, even though it is a bit difficult to work with, and it has been really waterproof after painting and caulking with the elastomeric patching compound. No leaks whatsoever inside the barn from driving rain.
