The reason people stud in the box walls is as much to improve the actual structure (the vertical planks carry the roof load _only through_ the nails which fasten them to the sills) as to gain insulation. The box construction was very quick and cheap to erect, at considerable cost to the permanence of the building and safety of its occupants. I'm amazed that many remain as do. They literally baffle engineers, because box houses fly in the face of every rule of structure.
Remove not the ancient landmark, which your fathers have set.
Do you have large beams at the corners? It may be post and beam construction. Perhaps even and old barn that was converted.
Be sure you live your life, because you are a long time dead.-Scottish Proverb
Dont know about the beams on the corners. All I know is it's solid walls. No air space
If the wall is structurally sound (and that's a subjective judgment I can't make here), then I see no particular reason to fur it out. Were it up to me, I might just completely cover the interior of the wall with foam board, then drywall over the top of that, using screws long enough to go through the foam board into the wood.
As for the structure, the existing boards may be sufficient to support the vertical load. They may not, however, be sufficient to prevent racking (shear). The foam board, if glued and fastened to the boards, and the drywall with sufficient fasteners properly installed, *may* provide good shear strength. (Only a structural engineer is qualified to advise you on this.)
The "Senior Member" designation under my name doesn't mean I know a lot, it just means I talk a lot.I've been a DIYer since I was 12 (thanks, Dad!). I have read several books on various home improvement topics. I do not have any current code books I can refer to. I was an apprentice plumber for two years.
The walls have been holding up for 80 years with no bowing or anything. I understand what you're saying about supporting the sheetrock. Guess that would be somewhat of a gamble on my part.
The only reason you should have any concerns for *causing the walls to sweat* would be if you had warm moist air from the inside contacting the cold exterior wall surface. If you properly attach the rigid foam to the exterior wall surface and completely seal all the corners , ceiling , floor , butt seams there shouldn't be a concern.
"" an ounce of perception -- a pound of obscure "
I live in a "box-built" house in southwest Virginia that was originally wall-papered with pages from a 1918 newspaper. Although it lists a little to the south and the east (away from prevailing winds) the structure is still sound. I enlarged an existing window opening to install a double window and nailed a rough-sawn 1x to the planks to serve as header 9 years ago with no problems observed. Structurally, a typical house built with 2x4/6 studs every 16 inches is over-engineered. A 2x4 every 8 feet could adequately support many of the vertical loads imposed on a structure. The 80 year longevity of your home speaks for itself.
A neighbour of mine (now deceased) studded the interior of his box-built home years ago, and updated the wiring and insulation to the standards of the time. It's fairly straightforward to fur the window jambs out to match the new thickness. I have used rigid foam in the upstairs end-walls of my 1 1/2 story house and observed no evidence of sweating. When time and money permit I will not hesitate to do the same in the rest of the house. Even if you stud the walls out for insulation and wiring upgrades (I ran wires in a custom baseboard) you can use still use panelling instead of fooling with drywall, just account for the thickness of the wall finish when extending the jambs of your doors and windows.
Pardon the delay in replying, I haven't been on the 'net much lately. I installed the foam directly to the boards with no air space (the space may provide a space for moisture to condense). I did install horizontal nailers to attach the wall finish, in this case 1/4 panelling. The foam board I used was salvaged from left-over scraps from a flat-roof project in the area. I believe it is a polyisocyanurate type, a closed-cell foamed plastic insulating core that is sandwiched between organic or inorganic felt facer. It has a thermal resistance of about 6.00/inch.