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I own a building which was built in the late 1800s. Somewhere in the Forties, the width was doubled. This all on pillars with a crawl space. In the fifties, a large warehouse was attached on a slab and cinder block chain wall. The entire building is in need of re-siding and I intend to use the 5” cement board lap siding to maintain the original look.

My question is about a suitable moisture barrier to use. On the original portion of the building there are vertical 1x12 cypress beneath the existing lap siding. I will not be removing the cypress, which means insulation cannot be added. The rest of the building will have exposed studs once the siding is removed and I can add insulation to those locations. The warehouse is unfinished with exposed rafters and studs inside. The floor and attic has no insulation or barriers.

Should I go with a moisture barrier with the wrinkled surface to allow any moisture an escape route behind the siding, a smooth plastic type barrier or look into one of the thin foil backed foam barriers (not the bubble type)? If I decide to finish the warehouse interior at a later date, should I add a vapor barrier inside at that point? Is it unwise to have vapor barrier in some areas but not others? At the front door recess area is vertical beaded boards. I do not intend to remove those at all.

Thanks for any advice you all may be able to provide.

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  • How large is the gap between the 1x12 boards? Cement board siding isn't usually supposed to span gaps.
    – isherwood
    Commented Apr 5, 2019 at 20:19

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With the rain and humidity in your area you'll want a breathable house wrap, not plastic or foil, and a drainage plane behind the siding to allow any water that does get through to drain away and dry to the outside.

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  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming!
    – Daniel Griscom
    Commented May 6, 2019 at 13:29
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I'm not sure what your particular concerns are but I'd do this...

  • Insulate the bare stud area and install modern OSB or plywood sheating. Taper it into the cypress 1x12s with increasing thickness shims over two or three studs.
  • Wrap the entire building with housewrap.
  • Install your siding.

I probably wouldn't install a vapor barrier inside, but you haven't told us where you are, what the climate is or whether you plan to heat the building. If you're in a truly cold climate and will heat you may want to line the interior with poly sheeting before you finish it.

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  • Apologies, I am located in south Louisiana between New Orleans and the Gulf. We endure high humidity and rainfall with about three weeks of winter and a lot of summer.
    – Frem
    Commented Apr 7, 2019 at 5:25
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    I don’t think I was clear on the cypress. The vertical cypress was the original siding. It had batten boards over the quarter to half inch gaps between the cypress. The batten boards were removed when the building was renovated to double the width and the entire building lap sided with the exception of the front entry recess which is vertical beaded board. My plan is to re-cover the cypress with cement siding rather than remove and replace with OSB. The cypress is still very sturdy. My main concern is a building that old with very little insulation, what is my best choice under the siding.
    – Frem
    Commented Apr 7, 2019 at 5:36

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