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1923 Balloon Frame – Insulation Questions

| Posted in General Questions on

As the title suggests, I recently purchased a 1923 house with balloon frame construction and have a plethora of insulation/air sealing questions. I’ll try to be succinct as I know this has been asked before, but I’m trying to do the best for my specific house.

To start, we had an energy audit performed which yielded obvious results….this thing is leaky. The contractor followed up with a spray foam insulation quote, which included applications along the foundation rim joist and attic roof rafters.

With the weather becoming increasingly cold this winter, we began to feel drafts (more like breezes) throughout the house, but most noticeably along a specific exterior wall. To investigate, I began tearing out drywall in the basement along the wall in question and was surprised to find mortar between the floor joists. The rim joist in this specific area was not drafty at all, so I assume spray foaming would not accomplish much.

I consulted a friend who builds/restores very high end homes and he was against spray foaming the rim joist in my specific situation. His reasoning included the potential for water to become trapped along the rim joist (it’s above grade) and the uncertainty of water ingress along the foundation. There is interior drainage along most of the foundation (except in the wall i started tearing up) which drains to 3 (!) sump pumps, so water was an issue in the past but I have not exposed the foundation anywhere else. He did suggest that I could use rock wool in the rim joist cavities if I decided to rip all of the walls open.

Back to the draft along the foundation. I traced this to an attached greenhouse and air sealed as best as possible. There’s also a nearby cold storage room beneath the front porch which was dug out by a previous owner. Both the cold storage room and greenhouse are very, very leaky. Yes, the layout of this basement is insane.

My current plan of action is to remove the existing drywall along the cold storage room and greenhouse, reframe, air seal, and add rigid foam board as insulation. I don’t believe water ingress is an issue along these walls as they are both kind of “interior” walls now.

My questions are as follows:

1. Am I on the right track as far as reframing and insulating the walls along the cold storage room and greenhouse? Can I spray foam along the stone foundation in these areas or should I consult with a mason about repointing, etc? The idea, at least in my head, is to isolate the greenhouse and cold storage room as exterior zones and stop air from infiltrating into the basement.

2. Anyone else concerned with spray foam applications along rim joists in a house such as mine? I’ve been researching and going into the weeds on this, but I agree with the concerns of my builder friend about spray foam. How am I ever going to know about a water issue behind the foam, especially if I finish the basement completely?

3. I don’t think I’ll ever get the basement air right, but should I be worried about ventilation issues as i air seal and/or insulate? No hvac runs down there, but I will likely add a mini split head to the basement in the near future. I ran a dehumidifier 24/7 when we bought the place in October and it would fill up with water every other day or so. I assume it will be very humid down there in the summer, and the dehumidifier will probably be sucking warm air from outside into this space if I don’t tighten up the walls. 

4. I’m confused by the balloon frame construction. In the attached rim joist photo, you can see two studs between the floor joists, which I assume run all the way to the attic. If these make up the interior side of my walls, I don’t think I can access the wall cavity from the basement. I assumed the air drafts I feel along the exterior walls of my house were due to air infiltration from the basement creeping into the wall cavities. Am I wrong on that? Should I be looking at possible openings on my exterior (currently vinyl siding over original wood)? I’m really confused by this.

I’ve attached photos of the rim joist, foundation exposure, and a 1st grade level drawing of the basement layout in this area. I can attach more photos if they help explain my situation better. Thanks again!

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  1. Balloon_Frame_10 | | #1

    I apologize for all of the multiple posts. I kept receiving an error message when posting so I assumed none of these actually posted. If a mod could remove all of the duplicates I would appreciate it!

  2. charlie_sullivan | | #2

    I'm not seeing the attachments.

  3. Balloon_Frame_10 | | #3

    Trying the attachments again, although I keep getting error messages.....

  4. Expert Member
    Akos | | #4

    A small amount of SPF is still somewhat vapor permeable, 1" of foam is around 1.5 to 2 perm, which is similar to dry OSB. The small thickness you need to seal up the area should not trap moisture.

    The bigger issue with insulating is not the foam itself, but the fact that the rim joist area is now colder. This will always add risk of rot, generally as long as bulk water is well managed and the area is well above grade, the risk of insulation is low.

    The cold storage area and greenhouse is best left outside your insulation envelope. Treat the walls separating it like an exterior, air seal and insulate accordingly. Also check that there are no large holes inside the celling to these areas as well.

    Balloon frame houses leak through the sheathing. The big issue with these is that your floor joist cavity is open to the wall cavity, which is open to the attic, creating a big hole for heat to escape through. The best way to deal with this is to dense pack the wall cavity. Installing blocking at each level and at the end of each joist bay also makes a big difference. Make sure to deal with your window/door flashing beforehand, these are non-existent in older houses and can cause a lot of damage after insulating.

    Insulating and air sealing the basement will reduce the amount of dehumidification needed but won't eliminate it. Generally, you'll have to keep the dehumidifier even if you add in a mini split head. Most of the cooling load there in the summer time is latent which mini splits can't provide enough of.

    1. Balloon_Frame_10 | | #6

      Akos, thanks for the info. That’s a big help.

      As for the wall insulation, I’m assuming this would be done via the attic or exterior drilling? The attic has insulation beneath the existing floor boards, but the goal is to bring the attic into the main building envelope as my hvac system is unfortunately located up there.

      Any specifics I should be on the lookout for (I.e installation methods, materials, etc) when I speak to contractors about the wall insulation?

      How do I install blocking at each floor bay? Can this be done via the exterior?

      Can you be more specific on the window and door flashing?

      Thanks again!

  5. onslow | | #5

    Balloon frame 10,

    I think the mortar was placed as a form of fire block, which is a good thing. The fact that they are smooth and flush with the subfloor boards makes me think it was done at the time of construction. Maybe they were really good builders and put in fire stops in the walls, too.

    I will risk countering Akos to advise caution with insulating the mortar filled joist pockets on the wall shared with the cold room. You have already noted extensive efforts to control water are in place, so I would suspect that the cold room could be more moist than the rest of the basement. If you try to insulate against the existing mortar, which presumably is in contact with what appears to be stone foundation, you could end up capping an important safety valve for wicked moisture. The joists look to be in good shape, so anything that changes the moisture load in the mortar might be against your long term interest. The constant load from the cold room could build up in the mortar if blocked on the warm side.

    My prior home was a botched up mess of western and balloon framing and as Akos notes the winds managed to make it through the siding, tarpaper, and boards with remarkable easy. The worst feature was how the winds also traveled across the underside of the second floor bedroom courtesy of the connection to the wall pockets. We would have filled the pockets with blown in, but as Akos also notes, the lack of flashing details around windows and doors can lead to problems down the road. Ultimately, we did nothing based on local market conditions rendering our house obsolete and doomed to removal. How are things above the basement?

    The breezy conditions you speak of sound like more attention needs to be paid to the connection points between porch and greenhouse. Maybe more pics from both sides of the wall would help.

    1. Balloon_Frame_10 | | #7

      Roger, thanks for the info. Sounds like you speak from experience on this one.

      Now that you mentioned fire blocking, my electrician noted slate at the bottom of an interior wall on the 1st level when running romex to the main electric panel in the basement. I remember doing some research online about this, but couldn’t find much info specifically related to slate and whether it would be used during initial construction or if it some sort of fire block retrofit.

      The 1st level is very leaky along the exterior wall mentioned in my original post. Again, my original intent when removing drywall along this wall in the basement was to look at the rim joist and see where air was leaking in. Now that I’ve opened it up and seen the mortar I really think the air is coming from the cold room and greenhouse, and then making its way through the various holes (radiator pipes, etc) in the flooring to the 1st level. Your comments about the cold room being more wet/humid than the rest of the basement are definitely correct and something I’ve thought about. I just don’t know enough about building science to make the correct call on this.

      The second level is downright comfortable except for one of the bedrooms directly above the leaky exterior wall in question. This was another indicator that led me to believe air was entering the wall cavity in the basement and migrating up the house.

      On the opposite end of the house a previous owner enclosed a porch, but only insulated the ceiling. Beneath that is a workshop of sorts that was dug out with a cinder block foundation beyond the original footprint of the basement, just like the cold storage room. No radiator in the porch, so it is very cold if we don’t leave the doors open to the main living space. The workshop in the basement is very cold and I can’t imagine the walls are insulated.

      Long term I’d like to either insulate the workshop walls or the ceiling to try and provide some benefit to the enclosed porch above, which has very thin walls preventing any sort of insulation retrofit. Insulation contractor told me to either bring this space into the main building envelope by insulating the walls, or leaving it as an “exterior” zone but still insulating the ceiling to warm up the porch flooring. Not sure if I want to tackle any of that, but I imagine cold air is seeping into the main basement space from the adjoining wall as well.

      Pictures attached are of the cold storage room walls from the interior and exterior. Thanks again for your comment!

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