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Sheathing to concrete gap fill

Spenceday | Posted in General Questions on

Have a semi odd scenario.
1950’s house, Zone 4A for reference
North facing alcove front porch

Originally the siding was installed and then the concrete front porch was poured. I am removing the vertical T&G siding as part of a larger renovation and to access the termite damaged rim. Plan is to replace the rim and any other damaged framing then install 7/16 Zip over the board sheathing and reside with a new Vertical T&G over a rain screen. I’ll install metal flashing from the Zip to the concrete (Risinger recently did this same detail in a video).  The rim will be sprayed with foam on the inside in the fall. 

My question is thus:
The old siding was 3/4 thick and there was no gap between it and the concrete. Once the 7/16 Zip is installed there will be a 5/16 gap between the sheathing and the concrete. There will be no airflow.
What should I fill this gap with?
Should I leave it open?
Is it a bad idea to put OSB into this space?

I could put something like a 3/4 PT into there that I coat with Copper Napthenate to discourage future bugs and then tape the joint to the Zip.

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  1. Spenceday | | #1

    Here are some pics

  2. Steve Knapp CZ 3A Georgia | | #2

    If it were my project, I would go with a band of exterior grade plywood where there is more risk of repeated wetting. I'd also check to make sure the concrete slab is angled away from the house.

    A few years ago I read a case study from a builder that had a somewhat similar situation (but maybe with more weather exposure). After rebuilding the wall, he cut a groove in the concrete and epoxied in a piece of custom formed stainless steel flashing that had been nailed and taped to the sheathing. That might be overkill here.

    1. Spenceday | | #3

      Slab does slope away and I really only get wind driven rain and snow all the way to the wall.
      The flashing detail is my plan here as well. Stainless flashing bent and placed into a grove cut into the slab and back filled with epoxy or probably Sika Crack Fill then taped to the Zip

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