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Ground floor cantilever protection

Jonny_H | Posted in Energy Efficiency and Durability on

Zone 5 (Ohio)

House has a section of the first-floor kitchen cantileverd about 2′ +/- with only about 12″ clearance to grade.  It’s also on the north side of the house, and will be adjacent to a deck, so it’ll definitely be a moist area that I won’t be able to inspect easily.  I’m planning to follow a detail similar to the one here: https://www.greenbuildingadvisor.com/article/insulating-a-wood-framed-floor-assembly — with the exception that the lower wall section is a masonry basement wall, and I’ll be doing an air barrier with Adhero on the interior side, coming down the wall (behind rigid foam), across the bottom of the cantilever, edge sealed to the masonry.  While there was some dissent in the comments of that article, it seems like it should be a safe assembly moisture wise…

My remaining question is the “cover foam with …. soffit material” part.  I want to use something that I won’t need to worry about for a long while, either in terms of moisture degradation or critters (ants / mice).  The critter concern seems to rule out any wood-based products, and since it’s a pretty small area I’m not going to be able to special order anything exotic.  Would it be appropriate to use fiber-cement trim boards like https://www.menards.com/main/building-materials/siding/trim-boards/allura-trade-1-1-4-x-8-x-12-fiber-cement-trim-board/1409062/p-1444450980598-c-13411.htm?tid=3914978467575240140&ipos=5 ? How about just 1/2″ Durock backer board?  Or should I be looking at aluminum sheet?

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Replies

  1. Walter Ahlgrim | | #1

    I have to ask why do a cantilever with no visual drama ?

    Seems like a small number of square feet why not put the foundation under it. Skip all the planning, building, energy and maintenance hassles for the cost of one or two yards of concrete.

    Walta

    1. Jonny_H | | #3

      Ah, unfortunately this is a remodel project -- though at this point I'm sure wishing I had built new, it'd certainly be easier, probably cheaper, and I could avoid things like whacky kitchen cantilevers!

  2. Kyle R | | #2

    Boral’s TruExterior trim is a poly ash composite that is rated for ground contact. Good stuff.

    1. Jonny_H | | #4

      Looks like there's a couple places that carry that near me, I'll check it out!

  3. Expert Member
    Zephyr7 | | #5

    I would consider PVC trim board here, the sheets that are similiar to plywood (they are commonly used for soffits). This materials is usually around 1/2" thick, it's impervious to moisture, won't rot, and critters won't eat it. Since your assembly won't really have any drying ability to the outside anyway, the PVC doesn't really have a downside here.

    PVC isn't chew-proof though, so if you're worried about that, I'd put some 1/4" mesh hardware cloth behind it as a chew-proof barrier. This way if something chews through the PVC trim, the steel mesh of the hardware cloth stops the chewing before the critter gets to the rigid foam and the interior of the structure. I've never found a problem with ants burrowing in PVC trim before, so you only have to worry about bigger "critters with teeth" here.

    Bill

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