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Discussion Starter · #1 ·
Hello,

I have two rooms over cantilevers. Both rooms have been showing condensation in the bottom corners of inside walls (drywall). So, this summer I removed the plywood soffit underneath the cantilever and insulated the cantilevers with foam boards, spray foam and Rockwool R-30. However, the interior walls are still showing condensation in the bottom corners. Any suggestions? maybe insulating corners from the inside?

Property Sky Building Grey Rectangle


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retired framer
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There is warm air circulation in both rooms (average temperature is about 67). I am trying to fix the main issue and not deal with mold later on.
The important detail is when the average is 67, what is the temp of the wall in question?
 

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retired framer
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Central heating with air vents not too far from corners. Other than a ceiling fan, perhaps insulating bottom corners?
Insulation will slow the transfer of cold or heat but it only works if you have both. It is a little like a closet on the outside wall when no warm air can move around in there, it will be cold and the moisture in the house will find those cold spots.
Usually you would have a heat register under the window and with a cantilever maybe they should be at the corners but then code says you want solid blocking over the lower wall.
 

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Your fix looks decent for outside air but not enough insulation. Should add at least up to r19 or more. All foam boards for least air movement. Since you can't do anything about sill plate joints, at least remove the base trims and foam the drywall gap. There's also the fact that maybe your inside relative humidity may be too high. If using a humidifier, check that. Amazon also has humidity meters. I've used a brand called acurite and it's been working for years. Can't say how accurate but over time, you can get your own base line. Hot air heating, I think, is supposed to dry the air, but I could be mistaken. My meter says 26% RH in the study, in nj, and my hand skin is drier and my throat dries out. Also hot air, so where are the ducts? Leaky duct?
 

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Discussion Starter · #12 ·
Your fix looks decent for outside air but not enough insulation. Should add at least up to r19 or more. All foam boards for least air movement. Since you can't do anything about sill plate joints, at least remove the base trims and foam the drywall gap. There's also the fact that maybe your inside relative humidity may be too high. If using a humidifier, check that. Amazon also has humidity meters. I've used a brand called acurite and it's been working for years. Can't say how accurate but over time, you can get your own base line. Hot air heating, I think, is supposed to dry the air, but I could be mistaken. My meter says 26% RH in the study, in nj, and my hand skin is drier and my throat dries out. Also hot air, so where are the ducts? Leaky duct?
The picture doesn't show it, but I added R-30 Rockwool insulation. The humidity meter shows ~45%. One room has a single air duct near the window, while the other one has two ducts on both sides of the window. At this point, perhaps I can remove the base trims and fill the drywall gap with foam, however I don't know the corner framing of my home (1977) and whether I will have access to them or I will need to drill to get the spray straw in there like this.
 
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