Insulating historic home- floor joists
Last Post 14 Apr 2022 03:54 PM by rgnbull74. 2 Replies.
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rgnbull74User is Offline
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13 Apr 2022 05:55 PM
Good afternoon- I have a home built in 1870 on piers. The house has no insulation of any sort, and we are beginning a full remodel. Since the home is in a rural area, there are issues with mice, possums, racoons, skunks- lots of animals that think insulation is great to tear up or sleep in. I am considering closing off the bottom of each joist area with 3/8" cell cure plywood screwed to the bottom of each joist, sealed from above with 2" of closed cell spray foam, and then batted with rockwool for the remainder of the enclosed space. The insulation will be added from the inside of the house before laying in the subfloor. Subfloor will be 1 1/8" plywood glued down and sealed around every joist, screwed down. Is there any concern with causing rot or damage to the house structure by insulating like this? I could use a 1/8" screen material under the joist to keep out vermin, but 3/8" plywood works as well and I don't mind the cost (buy once, cry once). Any suggestions would be great. I want this house to be very efficient and be around for my great-great grandchildren.
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13 Apr 2022 10:40 PM
You are thinking correctly and asking the right questions!

In general, you don't want to create cavities that can retain moisture. Moisture always gets in and it needs an adequate drying path to get out. What is "adequate" depends on the material used and humidity in the living space and the humidity outside. This calculator may be useful to you in making this determination and answering your questions:

https://www.borstengineeringconstruction.com/Building_Assembly_Moisture_Analysis_Calculator.html
Borst Engineering & Construction LLC - Competence, Integrity and Professionalism are integral to all that we do!
rgnbull74User is Offline
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14 Apr 2022 03:54 PM
Thanks! It's the deep south so humidity is always an issue. I'm going to play with the calculator and I may just wind up using the screen and rockwool. I am using exterior insulation on the walls and even though I really want to use iso with a foil coverage, it won't breathe. Probably will use Rockwool comfortboard there. Thanks again.
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