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Poly Vapor Barrier behind metal skirting?

last month
last modified: last month

I’m doing a shed to house conversion. House sits on concrete block pillars between 3 and 5 feet above grade. Ground below house is covered with black 6 mil poly sheeting. Bottom of subfloor (between joists) has sprayed on closed cell foam insulation. I need to add a skirting to enclose the area under the house. I was planning to build a frame out of treated wood and screw metal panels to the wood. I had planned to run poly sheeting between the wood framing and the metal panels to limit air infiltration and bugs. Poly sheeting for the skirting would be bonded to the poly on the ground with adhesive/tape, would run under base of wood wall and then turn up and run in front of wood wall but behind metal panels. Bottom of wood framed wall would be laterally pinned with 3/8″ rebar stakes driven through wood, through the poly sheeting and down into the soil 2 feet. I was planning on adding just the minimally recommended area of screened vents to allow moisture to escape from the enclosed area under the house.

What part of my plan is good? What part is not?
Thanks.



Comments (7)

  • PRO
    last month

    I would invest in something to protect the underside of the spray foam insulation from insect and/or rodent infestation. Provided the insulation thickness is adequate, I wouldn't do anything to limit ventilation of the space between the bottom of the joists and grade. If you want to improve the aesthetics, I suggest installing treated wood lattice in lieu of the metal panels you are considering.

  • PRO
    last month

    " . . . the minimally recommended area of screened vents to allow moisture to escape from the enclosed area under the house."

    Consider enclosing the space under the house (above and beyond code requirements) and heat, cool, and ventilate the space as if it is another room in the house.

    Metal panels corrode over time.

    Vents that let moist air out usually let moist air in also.


  • last month

    A WRB (e.g. Tyvek, Typar) is better than the polyethylene sheet on these skirt walls.

    The rebar stakes and wood sitting on the ground (even with the plastic under) is not the best scenario, but I don't know how far you want to take it.

    Metal panels will work with your flush T1-11 if you use mobile home prefab skirting so it limits the corrugation depth and has a nice transition cap (and bottom track).

    The passive ventilation is fine for how your crawl space is set up. Going unvented would require a bit more, and again don't know your context.

  • PRO
    last month

    Are those blocks core filled and rebarred? Is there a foundation poured below the frost line with the rebar extending into the block? There appear to be zero brackets holding the home to the block. You have uplift forces here that you need to engineer against or that shed is going to come right off of those blocks in a heavy thunderstorm. Every single thing needs to be firmly and permanently attached to each other from the earth to the roof sheathing.

  • last month
    last modified: last month

    It is not apparent in the previous photos, but there are 18 tie down anchors embedded in the concrete footings which support the block piers. Both vertical and diagonal tie down straps run from the anchors up to the 4x6 main girders. The girders are fastened to the joists with simpson hold down clips. At each wall stud location there are 4 hurricane anchors - a) from sole plate to joist frame, b) from bottom of stud to sole plate, c) from top of stud to cap plate and d) from cap plate to rafter.




  • last month

    @Delta Systems - Forgot to direct previous comment to you.

  • last month

    That closed cell insulation doesn't look right, it shouldn't look like it has dripped down the joists. You might take a core sample to make sure the mix was right on it.