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Community and Q&A

Is sheathing required behind clapboard exterior wall?

turtle_joe | Posted in Building Code Questions on

I have a 1971Lancer double wide mobile home with hardboard exterior walls that seem to be toxic. I am sensitized to chemicals due to chronic pain and fatigue. The hardboard has a strong petrochemical aroma when the sun heats it; or when i open up the wall space, such as when working on an 120v wall box. I have been around all the other house components before (vinyl, paint, carpeting, MDF, etc) and have finally realized its the hardboard that is the main culprit.

So i want to remove the hardboard and put on another exterior wall surface. I went to a cedar clapboard-maker site and they recommend placing sheathing over wall studs; then vapor barrier; then cedar clapboards. My existing wall has no sheathing and no vapor barrier. I have no perimeter support foundation other than hardboard skirting on flimsy 2×4 framing, most of which is not anchored or only loosely anchored to crumbling concrete footer.

I’d like to keep the replacement wall as light as possible, since the existing 1/2″ hardboard wall (4′ x 7.5′ panels) has 2×3 studs on 16″ centers and is light-weight. I’m considering building a partial-load-bearing perimeter foundation wall with 2×6 framing on a masonry/concrete footer. BUT keeping my overall costs low is a big consideration. I like the idea of real wood siding; horizontally placed clapboards would allow me to re-use my existing 2×3 studs(?)

What are some least expensive solutions using non-toxic components you can suggest for my exterior wall surface? I’m in a relatively benign climate area of California with 22″ of annual precipitation; and only about 10 weeks of night-time freezing temps in winter, little snow. THANKS, JT

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  1. GBA Editor
    Martin Holladay | | #1

    A hundred years ago, it wasn't unusual for inexpensive Vermont farmhouses to be built with clapboard siding nailed directly to the studs. But even back then, this was a method used by the poor. Anyone who had even a little money would first install board sheathing and building paper, and then install the siding.

    These days, building codes require sheathing and a water-resistive barrier (WRB) like housewrap or asphalt felt under clapboard siding.

  2. turtle_joe | | #2

    Since i have a problem with petrochemical vapors, which vapor barrier(s) would be the least toxic and/or Green?

  3. GBA Editor
    Martin Holladay | | #3

    Your wall doesn't need a vapor barrier, but it does need an air barrier.

    In most cases, your air barrier would be your sheathing (plywood with taped seams) or your housewrap (if the seams are taped) or your drywall (especially if you include airtight electrical boxes).

  4. Expert Member
    Dana Dorsett | | #4

    Unless you are in a high cold dry mountain pass you won't need (and probably don't want) a true vapor barrier anywhere in the stackup.

    Got a ZIP code for a quick & dirty climate check?

    Can we assume you have R7-R8 fiberglass or something in the 2x3 cavities? If yes, is there a facer in either side (or both), and what type? If a facer, which side- interior or exterior?

  5. turtle_joe | | #5

    I live in the Transition Zone at 1400 elevation, inland from the coast in a moderate humidity lake basin. Grass, brush and Oak Trees on heavy clay soil is the native landscape; zip 95457.

    I am NOT in a high cold dry mountain pass. I have fiberglass insulation but i have not had the entire wall apart to view the construction. Not sure what facing or R value. The place is cheaply made so i'm guessing it has the typical West Coast mobile home wall construction and insulation of the early 70's. I'm gonna guess it has thin building paper under the exterior hardboard siding. It has had the interior wall 1/4" wood paneling mostly replaced with 1/2" Sheetrock.

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