Below-Grade Rim Joist Protection and Insulation
Hello GBA community,
我在密歇根州安阿伯（Ann Arbor Michigan）有一个800SF的单层屋（气候区5）。这所房子建于1948年，拥有一个砌块地下室基金会。
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.
我正在考虑将此EPS板扩展到轮辋托梁的顶部。（因此，它将从地面沿砌块墙下方约2英尺处延伸，并继续越过轮辋托梁并直至边缘托梁的顶部。）我打算在ZIP-R和EPS板之间安装Z刷。
我担心创建腐烂或霉菌问题。(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.
任何评论或建议将不胜感激。
Thank you,
标记
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Replies
标记，
我可以想到两种解决这个问题的方法。
- The first is to excavate around the house and then build a short retaining wall about 12" away so that the grade was about 6" below the top of the blocks. You are then able to use any of the ways of insulation the rim joist area that are commonly used on houses.
- 您可以挖掘，取下壁板，用防水膜代替，并被某种类型的覆层覆盖作为保护。如果您选择此选项，则不会对外部干燥，因此应将墙壁设计成干燥，并保持边缘粘合区域安全，应具有足够厚的外部泡沫层。
I 100% agree with Malcolm's Recommendation #1 -- excavate and remove enough of the ground so that the rim joist sits ABOVE grade. Slope the ground away from the house while you're at it, so that water runs away from the house.
如果您无法进行挖掘，那么您会被固定墙方法所困。如果您走那条路线，我会深入挖掘它以放入一些排水瓷砖，然后填充洗涤后的砾石。这将限制泥浆溅到您的壁板上，并提供排水，以使您在房屋的基础周围没有水合。您需要将那条排水瓷砖排在某个地方...
Ideally you want any perimeter insulation to go down to at least the frost line, which is around 4 feet deep in Southeast Michigan (I'm a bit North of you near Clarkston). The easiest thing to do would be to just bury entire 4x8 foot sheets sideways, with the top up to the top of the foundation wall. XPS is a better material to use here than EPS. I would insulate the rim joists with EPS to allow for a bit of drying. On my own home, I put the EPS on the interior side of the rim joist since I have foil faced polyiso over the exterior side, and foil faced polyiso doesn't allow for any drying at all.
A capillary break between the top of the masonry foundation and the bottom of the wood framing will help prevent moisture/rot issues in the framing. This isn't as much of an issue if you insulate the exterior of the foundation as it is if you were to insulate the interior of the foundation, but it's still something that you really want to have in place.
Lastly, treating the rim joist with Coppercoat -- a wood preservative -- will give you a little bit of extra insurance from rot, but only a little. Coppercoat should not be considered to be a substitute for any of the more involved things that have been recommended to you so far.
Bill