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What to do with bottom flap of Typar + air seal edge of sheathing?

potton | Posted in General Questions on

My house in zone 6 will have perspirant walls (prefab walls) using 1-1/2 in of fiberboard as sheathing and outside insulation (three 1/2 in layers, the outer one being asphalt impregnated).   That outer layer overhangs the foundation wall [sketch attatched]

1) Must I add air sealing to the bottom edge of the asphalt impregnated sheathing?  

2) The prefab walls come with the Typar membrane hanging 1-1/2” below the sill plate level… What should I do with that flap?

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  1. Expert Member
    AKOS TOTH | | #1

    No matter what you do, getting fiberboard air tight is next to impossible. Doing a careful job with the house wrap helps but will never be as air tight as taped sheathing. If you want it well sealed go with a fully adhered vapor open WRB (liquid applied or peel and stick).

    With the WRB on the outside I think you can also skip the asphalt impregnated layer.

    For the bottom edge, the best is to install a layer of house wrap/poly/peel and stick under the sill plate, wrap this up and over the sheathing under the WRB. Seal the bottom of WRB to it with a bead of caulk on the backside.

    Critters tend to find any weak spot to chew through to get into the house. Make sure to have a solid critter barrier as well there (ie metal flashing extending out past the siding).

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