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Wall assembly

ramand | Posted in GBA Pro Help on

I am in zone 3 (Sacramento, Cali) considering the following wall assembly:

2/6, osb sheathing
wrb stucco wrap crinkly one (tyvek) AND 1 layer of grade D 60 min building paper,
lath and 3 coat acrylic stucco.
2 air barriers outside (taping the stucco wrap and sheathing seams) and at dry wall,
Insulation R23 Rockwool batt,
5/8 dry wall and level IV finish. 

Please advise if this can work. 

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  1. Expert Member
    ARMANDO COBO | | #1

    This is a typical wall assembly in the SW, works well and is affordable. The biggest issue here is to seal, seal and seal. Plan for good moisture management detailing on all openings and penetrations, even though you live in a dry area, and because of it, must builders are lackadaisical about it, and you see it often in rotted remodels.
    A good upgrade would be to install a three-dimensional stucco rainscreen system, and there are many options on the market, like DELTA-DRY Stucco & Stone, Tyvek® DrainVent™ Rainscreen, HydroGap SA, etc.
    Another good option is to install 1" sealed and taped rigid foam on top of the sheathing. If taped with approved tape, it becomes a WRB. The rigid foam works against thermal-bridging, and if you can get reclaimed foam board, it becomes more affordable.
    You could replace the mineral wool for dense-packed cellulose. Rockwool is a great product but costs more, and the change can help offset the rigid foam, a far better wall insulation factor.

  2. ramand | | #2

    Thanks Armando
    I am thinking Tyvec house wrap with Drain Vent. Any issue with vapor permeance? I know professor Joe recommends perm rating of 10-20.

    Is it ok to tape OSB/Ply seams? My stucco guy likes 1/8 inch gap between two sheaths to allow for expansion/contraction. Does taping affect it?

    Lot of production home builders in Sac are doing tyvec or building paper > 1 inch EPS and than 2 coat stucco.

    Does acrylic stucco also soak water like cementous 3 coat? any preference?

    I can do dense pack cellulose over rockwool. Any advantage from moisture problems for one over another? I was thinking of rockwool due to added sound effect and fire resistance.

    Thank you for your time

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