Below-Grade Rim Joist Protection and Insulation
Hello GBA community,
I have an 800sf single story house in Ann Arbor Michigan (climate zone 5). The house was built in 1948 and has a block wall basement foundation.
The basement has a nice ceiling height, about 8 ft, but it seems as if the builders dug the hole for the foundation too deeply: the house sits so low in the ground, that the bottom of the rim joist sits about 4 inches below grade. I believe additional top soil was added over the last 10-15 years, probably just before the house was “flipped”.
The exterior walls are covered with cedar siding all the way down to the block foundation (so the last two rows are now below ground.) Someone added a row of Hardy plank over the cedar siding where it is below ground, but that doesn’t actually provide much protection since the bottom of the cedar is still exposed to the soil.
I want to remove all of the cedar siding and add ZIP-R sheathing and then some type of cement siding. I know the ZIP sheathing cannot be placed below grade so I am currently planning to stop the sheathing at the top of the rim joist.
I also want to dig a few feet around the perimeter of the house and install 2 inches of EPS insulation over the block wall.
I am thinking of extending this EPS board up to the top of the rim joist. (So it would run from about 2 feet below ground along the block wall and continue over the rim joist and up to the top of the rim joist.) I intend to install a Z-flashing between the ZIP-R and the EPS board.
I am concerned about creating rot or mold issues. (I have not noticed any existing issues in the rim joist yet, but I have not removed the cedar siding yet either, so I don’t know what it looks like… I have found rot in other parts of the above grade wall – due to rain.)
Also, I believe the wood simply sits on the block wall without any type of gasket between the block wall and the rim joist.
Any comments or suggestions would be appreciated.
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