Your region may have sustained cool foggy weather and high moisture. Mold, algae and other growths can be found on any surface that provides a moisture and food source. Tyvek is permeable to air and vapor and is an inorganic spun-bonded polyetylene fiber. Like plastic (polyethylene sheet)it does not support mold growth; but unlike plastic, it can breath. This actually promotes drying in the wall void. Since moisture is persistent on the PNW coast, moisture traped between the barrier and organic siding may cause mold growth on siding.
On the otherhand, building paper is an organic felted paper and can absorb moisture and support mold. Felts are normally asphalt saturated to form an effective weather barrier and used as roofing felts and weather barrier under siding. Asphalt saturated felt does not breath. Under persistently moist conditions, this surface is more likely to trap moisture aginst siding or sheeting, and support mold and other plant growth due to the absorbent organic felt core and breakdown of the asphalt. Felt is less expensive, easy to apply, and is more easily damaged during construction.
Tyvek and other spunbonded synthetic fibers allow air to move slowly through building shell promoting drying, but stops wind and liquid water. In this case, it is a clearly superior modern product. In most installations, either felt or spun-bond barriers will work fine. The extra expense of the synthetic barrier is probably worthwhile for you. |
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