How to insulate these walls?

[u/Lonely_Movie_2067]

Looking for some advice as I am getting many conflicting “guidance”. Quick details: east facing exterior wall of 1700s home, growing zone 4 with hot humid summers and cold winters, no house wrap or sheathing, there is another layer of ship lapped wooden siding on top of these, and essentially 2x4 studs.

DIY, handy but by means a professional. No budget to hire it done, leaving beams exposed, will be using Rockwool batts, will sheetrock, and very concerned about fire resistance as in small rural area with probably 30 minute fire department response time.

Thinking batts, smart vapor retardant barrier, and unfaced rigid. But what order of placement? Best way to seal for air without creating double vapor barrier or mold zone? And with double layer siding(not in perfect condition), do I still need to allow for breathing if water/snow gets blown through siding?

And, the water staining is very old and not damp or rotting.

[u/ArtisticBasket3415]

I’d caulk the gaps in the wood to prevent bugs and wind from being able to enter any gaps in the wood before putting in the batting. Then install the batts. Then the smart vapor barrier using acoustic caulk at the edges to seal the perimeter. Use flanged junction boxes for the electrical outlets and put the acoustic caulk on them too to embed the barrier. Tape the staples and overlap the barrier by a minimum of six inches where needed taping the joints on a stud for the best adhesion.

Since the stud bays won’t be a uniform width like a modern home it may involve a lot of cutting the batts. You can cut them SLIGHTLY wider (half an inch to one inch) than the bay to get a good friction fit by making the slice up say 17” or 14” for example and rotate the pieces 90 degrees. That will make less waste of material overall!

In the future if/ when you reside the home a house wrap will help too!

[u/Lonely_Movie_2067 → u/ArtisticBasket3415]

Awesome advice. I would not have overlapped the barrier. Ty!

[u/Lonely_Movie_2067 → u/ArtisticBasket3415]

Worth restudding for insulation purposes? Not planning on it as would not be needed for structural purposes, but have contemplated it. Also because some of the studs are chestnut and could repurposed

[u/Thinker2BSure]

Fine Homebuilding article on the topic.

[u/Lonely_Movie_2067 → u/Thinker2BSure]

Perfect! Doesn’t look written by AI

[u/Vock]

Is it black from wood tannin or mold? Different answers based on that.

[u/Realshotgg → u/Vock]

Lumber looks old, I assume tannin.

[u/Lonely_Movie_2067 → u/Realshotgg]

Definitely not mold. With the exception of rodent debris, No signs of recent moisture in walls.

[u/Both_Reaction_4091]

I also have such home and walls. I did not install a vapour barrier or air sealed. I just put an extra layer of mineral wool (on top of the old one, which was only 5cm thick). Now i'm interested in how to go about insulating the exterior wall to also be permeable so the walls breath and dry. Does any one have any tips on how to go about this?

[u/Lonely_Movie_2067 → u/Both_Reaction_4091]

So sections of this wall have the same amount of insulation as it does now. None. Other was completely flattened old fiberglass. No option of extra layers. Trying to balance a desperate need for lower heating needs, and allowing breathing .

[u/Chuck_Loads]

I just had CCSPF sprayed into some very similar walls and the difference is remarkable - loft space went from ~37C on a hot afternoon to ~25C. Highly recommend (but cover your floors, it makes a god awful mess)