While we United States residents like to think of ourselves as perhaps the center of our universe, post frame construction appears world wide.
Reader JONATHAN in HALIFAX picked Alabama as his state when he filled out his online request for information when he wrote:
“What insulation do you suggest between bookshelves of wall?”
With so many post frame buildings being used for residences, commercial buildings, shop/houses and barndominiums, properly addressing how to insulate has become of utmost importance.
I am going to take a stab and guess your Halifax is in Nova Scotia, rather than Alabama. My lovely bride and I made a stop there on a cruise from New York City a few years ago – beautiful area (and I got a Harley-Davidson T shirt).
If so, you are in what would be an equivalent to our IECC (International Energy Conservation Code) Climate Zone 7. For wood frame walls, this would require an R-20+5 or R-15+10, where your plus value is for continuous insulation.While continuous insulation is most often usually on exterior of framing, Martin Holladay – editor of Green Building Advisor feels confident in it working as well on inside of framing. Given this, I would put a Weather Resistant Barrier (https://www.hansenpolebuildings.com/2016/01/determining-the-most-effective-building-weather-resistant-barrier-part-1/) between wall framing (bookshelf wall girts) and siding, then fill your cavity with rock wool (as it is not negatively affected by moisture), then use rigid foam insulation inside of your framing. You can glue these sheets to your framing (bookshelf girts) to eliminate any thermal bridging from fasteners and then glue your interior finish to it. Make sure to tightly seal your rigid foam boards and to caulk along the bottom of exterior walls to get a good seal. Built in this fashion, your walls will ‘dry’ to the outside, reducing the need for dehumidifying inside.
Of course you will want to get approval from your local permit issuing jurisdiction before moving forward.
For extended reading on rock wool insulation please see https://www.hansenpolebuildings.com/2013/03/roxul-insulation/