More Q&A Spotlight
Prior to the advent of building codes and the wide distribution of standardized materials, home builders often relied on local traditions and their own experience to guide them in the construction of houses. The results include the many surprises modern owners of those homes find when renovating. Often, those findings complicate project plans.
Member “thearrow” (aka Jake) writes in this Q&A that he is renovating a late-1800s house in southeast Michigan (Climate Zone 5A) and he wants to add insulation to the walls. Like many of the homes built in that era, the structure is balloon-framed, so the stud bays are open from the foundation to the top plates. Jake’s illustration shows successive layers of previous remodels, including the unusual use of horizontal 1x10s fastened to the interior of the framing, beneath the plaster and lath. He’s curious about the purpose of the 1x10s, wondering if they are structural and whether they should be replaced them with sheathing.
He sketches his options for how to approach the renovations. His first thought is to strip the interior down to the studs, add blocking, air-seal the bays, add R-15 mineral wool, install a smart vapor retarder such as Intello Plus, and finish with drywall.
One reader suggests he could modify that plan by removing only the top and bottom 1x10s; then add blocking, air-seal, and replace the 1x10s. To insulate he could drill a few holes in the drywall for blown-in cellulose. One caveat with this approach is that cavities couldn’t be completely sealed.
His third option would be to work from the exterior. That would entail removing the vinyl, original siding, and weatherproofing layers, then add blocking and insulation, new sheathing, a water-resistive barrier (WRB), and siding.
Jake writes that after…
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8 Comments
Wow, thanks Chuck and Jon! I appreciate having more eyes on this project. Really glad to hear you agree with the exterior approach, despite its challenges!
Currently still planning this out and haven’t started opening up the walls yet, but I’m sure I’ll be asking more questions as we proceed ;)
Are you sure you want to put the vinyl siding back on your historic house after all that work? :) There are better looking composite and fiber options! I imagine the old vinyl siding might be hard to remove and reinstall without looking beat up.
Always open to suggestions! :) Agree that the siding might get beat up during re-installation, and it's not in particularly pristine shape to start with. I've considered things like LP SmartSide and Hardie Plank Lap Siding, and would love to do something like that if the budget allows... What product would you choose?
What about when we have an existing wall assembly in this order starting from the outside-in:
Climate zone 4A:
Painted wood lapped siding (no intention on covering or replacing) over
True 2x4 studs with open cavity (no insulation) over
1" Lath & Plaster finish (painted obviously) (client is willing to replace all interior with new GWB).
I would argue a good way of insulating would be to:
-remove all interior lath & plaster
-install unfaced mineral wool either 3" (sound batt) or 3-1/2" (comfort batt) while leaving the 1/2" or 1" gap to the outside so that there is a convection space between the batt and the outside siding.
-Install GWB and paint, paint shall act as vapor retarded as required for zone 4A.
Even if this was Zone 5A where a traditional vapor retarded is required, I might argue that a smart membrane would be good/better but not totally needed since the lapped siding alone (without 4x8 sheet sheathing) is never a good air barrier thus should allow plenty of moist air to escape.
Also I try to avoid GWB penetrations at exterior walls as much as possible (moving power & switches to interior walls where possible) as well as paying close attention to cooking, laundry and bathroom exhaust so that the home's inside air is kept as dry as possible.
Rick,
You may find this article useful. https://www.greenbuildingadvisor.com/article/managing-water-and-insulating-walls-without-sheathing
I don't love that solution that doesn't allow bulk water intrusion from lap siding to dry to the inside. I think that solution is decent if the lap siding is incredibly open and breathable but if it's lap siding with 100 years of paint, I'd rather only have one layer of mineral wool and GWB between the relatively dry inside air and the cavity between the lap siding and mineral wool.
Rick,
Maybe a good approach would be a permeable barrier like house-wrap forming the air cavity rather than foam, which could both stop water intrusion through the siding getting any deeper, but also allow drying to the inside?
I'm not sure I'd trust just batts to keep a small cavity clear. I'm also not sure it's worth just ending up with 3" of permeable insulation in the walls if you have gone to all the trouble of removing the lath and plaster. Either making a Mooney Wall, or adding continuous interior insulation seems like they would be a good idea.
Probably the most important part of the new assembly would be a good interior air-barrier. That could be the drywall, a variable-perm membrane, or foam board.
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