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Will wood siding pass capillary water into wall assembly?

Richard Baumgarten| Posted inGreen Building Techniqueson

Hello-
I’m planning to build a low-toxicity cottage. Siding will be unpainted horizontal cedar, on vertical rainscreen furring strips, with an asphalt felt WRB, ADA interior, and insulated with wool or cellulose.

The bottom of the siding will be about 10″ from the ground. I’m worried that moisture absorbed by the siding (from rain, or snow melt) will pass through the furring, the sheathing, and into the organic insulation through capillary action.

From what I’ve read, I don’t know if I can trust plastic housewraps (surfactant issues), or moisture wicking asphalt-felt to stop water in its tracks. I was thinking of putting strips of metal, or poly behind the furring strips, would this be overkill? Would there be condensation issues?

I have mold allergies, so I’m a little paranoid….and I don’t have enough experience to know what I’m getting into.

Thanks for your help!
-Richard

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Replies

  1. GBA Editor
    Martin Holladay||#1

    Richard,
    Relax. Your planned assembly sounds fine. Asphalt felt is a good WRB, and the ventilated air gap between the siding and the sheathing will prevent the sheathing from getting wet and will encourage rapid drying.

  2. Bill Bradbury||#2

    Remember to install water table flashing and you should probably apply a non-film-forming UV protecting oil such as Penofin to the unpainted cedar.

  3. Richard Baumgarten||#3

    I was going to go without a water table. It makes sense to have one if it's PVC, but with no air space behind it, is wood a good idea?
    Penofin sounds interesting, "extracted from fallen nuts of the Rosewood tree", but contains an unknown nano trans-oxide pigment.

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