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Community and Q&A

Insulating balloon framed house

Bryan_K | Posted in Energy Efficiency and Durability on

My wife and I are about to purchase a 1947 home in Vermont. I believe it is balloon framed because the attic deck doesn’t cover the wall cavity. The house has very little insulation. We plan to add insulation but are struggling with what to add, and where.

The basement walls, box sill and first floor floor framing aren’t insulated. The seller disclosed the basement gets wet in heavy rains and when the snow melts in the spring. The house is toward the bottom of a hill.  We plan to mitigate this with adding gutters and day-lighting the 3 sump pumps (currently one just dumps the water next to the foundation). We want to see if that helps before doing anything more drastic. But I digress.

I’m hesitant to insulate the basement walls because of the moisture issue. So I’m thinking about doing a flash coat of spray foam under the floor framing.  

I don’t know if there is insulation in the walls. It looks like fiberglass has just been stuffed into the top of the 2nd floor wall cavity. The attic is 2×8 ceiling framing with gable end vents, no soffit vents. The ceiling framing is covered with 1 by material (not plywood). I’d like to keep the attic as usable, storage, space. Loose fill cellulose would take away this as storage space. I’d rather not close off the vents and insulate the rafters. Should I spray foam the wall and rafter connection point? I’m cautious about creating a dew point between two different types of insulation. Maybe I’m overthinking it.

I’ve read conflicting reviews about insulating the walls in old house like this with plaster walls because of a lack of vapor barrier. I would think that 70 years of painting and repainting would seal the plaster. Although air would still leak through penetrations.

Thank you in advance for the guidance.

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  1. Expert Member
    Akos | | #1

    I would read through some of the other posts about insulating balloon framed houses and come back with specific questions related to your situation.

  2. BrianPontolilo | | #2

    Hi Bryan,
    As Akos said, it's tough to offer too much without specific questions. However, I think you may find the articles below helpful.

    Unless your basement has bulk water problems, you should be able to insulate the walls. Here's a how to on that: How to Insulate a Basement Wall

    If there are bulk water problems, you'll need to take care of that first. This should help: How to Fix a Wet Basement

    Since the most common way to retrofit insulation in a home like yours is to install dense pack cellulose. This should be helpful: How to Install Cellulose Insulation

    The installer should know what to do to make it work in balloon framed walls. If they don't, find another installer.

    Finally, these two articles will be helpful, whether you decide to go with an insulated roofline or an insulated attic floor: How to Insulate an attic floor How to Build an Insulated Cathedral Ceiling

    Please ask more specific questions as you have them.

  3. Expert Member
    Dana Dorsett | | #3

    The window flashing details and air leakage from the interior are far more important considerations than lack of a vapor barrier. Almost all alkyd/oil/lead paints are approaching Class-I vapor retardency, but a square inch of air leak can move more moisture in a season than a whole wall of UNpainted plastered wall.

    Air leaks to the exterior often save old uninsulated balloon framed houses from bulk water leaking in around windows or window blown through the siding, so it's important to rectify any flashing defciencies before insulating, and take a good hard look at the siding and weather resistant barrier layers to make a judgment call.

    Even though cellulose is greener overall and can safely buffer a lot of moisture relative to interior side moisture drives, if the exterior side details are only so-so, low density blown fiberglass dries a lot quicker and might be the better choice.

  4. Bryan_K | | #4

    Thank you all for the links! lots of good information.

    I'm thinking about leaving the wall cavities as they are, insulated or not (at least for this winter). Then sealing off the wall cavities in the basement and attic. As well as air sealing the electrical boxes. If the flashing detail at the windows is okay, I doubt it's really good, should I be concerned about mold growth inside the wall cavity? I believe there is sheathing behind the siding.

    Thanks again.

  5. Nojak | | #5

    In our 1899 house, also balloon framed, the previous owners gutted it and redid it with fiberglass batts and 6mil poly. And terrible detail to that process as you can feel drafts when the winter wind blows.
    I'm not convinced you can properly seal a poly VB in this type of framing. Trying to find all the air leakage is quite the process.

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