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Community and Q&A

Rainscreen with furring on 30# felt WRB

Thomas Kammerer | Posted in Energy Efficiency and Durability on

Hello GBA,

What do people think about using 3/8in thick furring strips @ 16in o.c. over 30# Felt (ASTM D226 Type 2) as a rain screen gap/WRB assembly?

The furring would be either 3/8in x 2in plywood strips or Cora-Vent Sturdi-Strips and would be ventilated top and bottom with Cora-Vent SV3 siding vent/bug screen. The plywood strips would be borate treated to prevent powder post beetles and rot problems in the furring strips.

Would “puckering” of the 30#felt when it absorbs moisture be a problem?

The location is on the Oregon Coast (Climate Zone 4C) about 1/4 mile from the ocean. This is new construction and a rain screen gap or drainage material is required in Oregon.

Thank You
Tom

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Replies

  1. Malcolm Taylor | | #1

    Thomas,

    You should be fine, but a 3/8" gap and 16" oc strapping means you may get spots where the building paper wrinkles enough to touch the cladding in spots, creating a capillary bridge. That's one of the main reasons I prefer house-wrap behind shallow strapping.

  2. User avatar
    Peter Engle | | #2

    Felt also doesn't give you an air barrier. So long as you have another air barrier material, that might be fine.

    I wouldn't worry so much about the felt wrinkling and touching the cladding, because it will flatten out again as it dries. Probably won't change the overall drying potential of the wall much at all.

    A benefit of #30 felt on the outside is that it's naturally a "smart" vapor retarder. It'll slow down vapor drive from the exterior when it is dry, but allow drying both ways if it gets wet.

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