Hi. I have a small farm in southern Maryland (i.e., humid) with several outbuildings that I believe were bulit in in the early 1980’s, including a small barn and a separarte workshop. Both the barn and the shop building were sheathed in reverse board-and-batten plywood. The barn was painted but is otherwise uninsulated/unifinished inside and is not conditioned at all. The workshop sheating was left exposed (appears never to have been painted), the workshop is heated and cooled and is insulated with paper-faced fiberglass batts in a 2×4 stud wall with interior drywall.
The plywood on both buildings is structurally intact but has seen better days and I would like to re-side both structures with verical board-on-board siding (or shiplap), probably cedar with a semi-opaque stain on all sides. My initial intention on the barn was to add horizontal blocking inside and nail up the vertical siding through the existing plywood and into the blocking. I would expect that there is no vapor issue as the space is not conditioned, but I got to wondering if this would create any issues with trapping moisture between the vertical siding where it lays flat against the existing plywood sheathing? To address this my thought is to secure the vertical siding to horizontal strapping applied to the outside of the existing sheathing instead of internal blocking, with the existing vertical “channels” in the reverse board-and-batten plywood allowing ventilation and drainage as needed. Overall I think this might be a preferable design and an easier install all around as compared to the internal blocking. In either case the cavity created in the wall would seem tailor made for bug nesting – would anyone recommend closing off those channels at their lower end with some sort of air/water permeable mesh? products for this?
Turning to the workshop, I would rather not distub the drywall to add internall blocking and so would like to use the same horizontal strapping detail to hang the vertical siding. I would also like to add housewrap over the sheathing before the strapping is applied, and – if there is any way possible – to add a layer of rigid foam board insulation. Does anyone see any vapor issues with the addition of the housewrap to the wall section described? Would anyone care to weigh in on whether a 1/2″ layer of polyiso board (with or without reflective foil) applied between the sheathing and vertical siding would be worth the effort? If so where does it go relative to the housewrap and are there any critical details you could point out (taping, adhered, etc.)?
Thanks for any input or advice you can offer.
Regards,
Chris