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Insulating a 1890s house

oldhousesam | Posted in Energy Efficiency and Durability on

I think i have confused myself reading around on here. I have a house built in 1890ish and its cold. I now have to insulate. I dont want to remove the original siding and trim to insulate the outside which is the most ideal way so i have to insulate the interior side. Its true 2×4 construction 16 on center with ship lap siding with wood siding. I was thinking about using a batt insulation with a air (and vapor?) barrier with 2×2 horizontally to bring my utility’s on the inside of the insulation and maybe a vapor open insulation(pink fiberglass) in the 2×2 just to bring the average r value up. Is there a better away of achieving a good insulated warm sealed wall? will this idea work? the house is 5700sqft so every little helps.
Thank you

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  1. Expert Member
    Dana Dorsett | | #1

    Where are you located (it matters!)

    I assume you meant ship-lap SHEATHING, plus wood siding? Is there anything like rosin paper or tarpaper between the ship lap sheathing and exterior siding? And the exterior siding is what, clapboards, shingles, board & batten or ... ???

    1. oldhousesam | | #2

      I guess i left out a lot of needed info. Im in the climate zone 6 of Pennsylvania. Yes i did mean sheathing(dam auto-correct and lack of proofreading), and in the gaps of it i cannot see any paper just the back of the clapboard siding.

  2. Jud_Aley | | #3

    If you want to insulate from the inside are you planning to gut the entire interior to the frame? If yes, that means removing all the interior trim, plaster etc.... a huge job, probably a much better idea to insulate from the exterior, easiest way to do that is with blown in dense pack cellulose, have you looked into that? What do you mean when you say "bring my utility’s on the inside of the insulation"

    1. oldhousesam | | #6

      Yes its a gut job. we brought for cheap from tax auction and the place has been neglected and abused. the roof has leaked down a few of the walls so the lath and plaster has to be removed. The house leaks enough air the structure is rot free. I dont want to disturb the siding due to the fact its original(so i have been told, and it looks to all match with the local 1920s fire map).
      I mean when i say bring my utility's on the inside of my insulation is i can have the outlets and such on the interior side of the insulation, so insulation behind them. I see cold outlets and light switches are common and seem like a good way of loosing heat. It also lets me put a washer and dryer next to each other on a outside wall without worrying about heat lose from the hot pipe or freezing the cold.

  3. Expert Member
    Akos | | #4

    Since you don't have a wrb, your situation pretty close to this:

    Since there is boards under your siding, you can probably get away with no air gap, just stapling some housewrap into the inside of the cavity to provide some protection for the insulation. No air gap does increase the chance of your siding paint peeling, there is always a chance of this when insulating old houses.

    Adding in and insulating the 2x2 cross strapping does buy you a fair bit of R value (brings the R12 assembly close to R20), cold enough climate that it is probably worth it. Might be easier to do if you can dense pack the walls.

  4. Expert Member
    Dana Dorsett | | #5

    What Akos said- it's very similar to dealing with a house that has no sheathing. While you can probably get away with stapling a weather resistant barrier (WRB) to the back side of the sheathing, pay close attention to how bulk water is managed around windows- odds are there isn't any pre-existing flashing. I'd personally be more comfortable building in a weatherproof exterior air barrier for the insulation, with half-inch air gap between the air barrier & sheathing.

    Half inch foil faced polyiso would be a good choice leaving 3" to compress your batts into. R13s would perform better than R11 when compressed to 3.0", half-inch polyiso is good for ~R3, the foil facer next to the gap is good for another R1. Cutting narrow 3/4" -1 " wide strips as spacers tacked on both sides of each stud, and another mid-way between the studs makes it rigid enough to not bow out from the compressed batt over time. The drying path around the foam layer from the insulation into the gap is pretty good even through an inch of wood.

    This is of course more labor intensive than stapling in some Tyvek. If taking the latter route, use a crinkle type version (eg DrainWrap), which offers at least SOME capillary break limit the rate of moisture wicking further in toward the interior.

    You absolutely DON'T want to just blow the cavities full of cellulose if there's no WRB between the sheathing & siding, and no window flashing. That would all but guarantee paint failure on the clapboards in short years (or even months), followed by mold/rot getting going in the sheathing & framing on the less-sunny sides of the house a few years after that.

    In zone 6 you'll need the air barrier between the 2x4 & 2x2 cross framing to be fairly vapor retardent. While 4-6 mil polyethylene would work, a smart vapor retarder on the lower-permeance end of the scale such as Intello Plus would be safer if you're also insulating the 2x2 cavities.

    1. oldhousesam | | #7

      Thank you, you gave me much more to think and read about. So im thinking the polyiso will be the best choice seems as it will be easier to keep consistent all the way up the walls(ballon framing with 12.5 foot ceilings). Should i seal it like with poor mans spray foam method? and should i vent that to the outside through the header and footer?
      Thank you again for all of this information

      1. Expert Member
        Dana Dorsett | | #8

        Sealing the edges to the framing with can foam works. The seams between sheets of polyiso can be sealed with a high-quality aluminum HVAC tape (eg Nashua 324A, found in most box stores.)

        The primary purpose of the vent gap is as a capillary break and drying channel for the sheathing. With plank sheathing and no tar paper or rosin paper it's usually leaky enough to be inherently vented, but if it's easy to vent it to the outdoors, go ahead. Something like ~1" round screened vents should work, one at the bottom of each stud bay, and where blocked by framing, another at the top. Most balloon framing vents into a vented attic, so as long as the attic is vented that should still work. Be sure to seal the top of the cavity above the fiber-insulated fraction.

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