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Air Barrier Placement – Zone 4C Salish Sea

alderwiser | Posted in General Questions on

First posting on this incredibly insightful forum…somewhat addictive.

I live on Whidbey Island where it is usually under 60F and very windy in different ways throughout the seasons. My question is based off of  recommendations on this forum for a 4c climate, to place the primary air barrier to the outside of the wall assembly (using taped sheathing and a rainscreen). This obviously makes sense for keeping out cold air, but with a low dew point most of the year here, reducing humidity, is there less of a concern about vapor driven into the wall assembly from outside, compared with interior warm moisture pushing outwards? In other words, is having an interior air barrier/smart membrane more prudent than taping CDX seams for this climate?

I’m sure this is a “depends” question. So here is the info on my second go at a wall assembly for the house my wife and I are designing (exterior air barrier):

Horizontal Cladding
    Open Joint or Live Edge Clapboard Wood
Rainscreen 1×4 Vertical Batts 24-32″ o.c.
W.R.B. Solitex Mento 1000 or Fronta Quattro
    Seams taped with Tescon Vana
1/2″ CDX Sheathing
    Seams Sealed with Visconn Adhesive (A.B.)
Double Stud Wall
    2×4 Exterior Load Bearing wall       
    1″ (or >) gap   
    2×4 Interior wall   
    Blown-In Cellulose Insulation R-28 min.
        Dense Packed to 3.5lb/cu.ft.
1/2″ Drywall or Wood paneling on Fronta Quattra

The other assembly uses intello as the air barrier on the inside wall and a chaseway inside of that.
Either Assembly will include:
– 2x Joists above a walkout basement, with subfloor taped.
– Gable Vented Trusses, Loose fill Cellulose, Intello AB on Ceiling (somehow connected to wall AB)

I am a Carpenter/new GC and have used the 475 products a few times now. I will be doing most of the work myself.



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