OSB sheathing "below grade"


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Old 03-29-12, 09:16 PM
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OSB sheathing "below grade"

I'm in the middle of replacing my siding as well as insulation/sheathing. While tearing out the wall within my covered porch, I discovered that the siding and existing foil faced foam sheathing extended below the concrete porch. In other words, the porch was poured after the house was sided. I did somehow manage to remove everything despite the fact that the siding was face nailed beneath the concrete, and now I'm trying to figure out how to proceed.

Here is a picture of the shortest wall on the porch:
https://picasaweb.google.com/lh/phot...eat=directlink

I definitely won't be putting siding down the gap, but I wasn't sure if I should let the OSB sheathing I'm installing extend down to the ground. I'm hesitant to do that because of potential rot issues. While the porch is covered, it isn't spared from wind blown rain and snow. If I did extend the sheathing below the level of the porch, I would probably try to seal the band board (pvc trim) to the porch with silicone. Alternatively, I was thinking of filling that crevice with expanding foam, and cutting the sheathing flush with the porch floor.
 
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Old 03-30-12, 03:21 AM
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Wow, there's "wrong" and "wronger". You got both. The framing lumber below the concrete face will suffer water damage, no matter how you treat it. Spray foam is not waterproof and will provide no protection for the exposed wood. Any other wood you send down the hole will suffer the same fate. Bringing your siding to the top of the concrete with adequate flashing all around to deflect water may help alleviate wind borne water, but I worry, now about water seeking its way into the crevice from below.
 
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Old 03-30-12, 01:05 PM
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How would I flash the siding in this case? It seems like whatever I do would need to extend past the foundation which is nearly impossible with the amount of space I have to work with. I know I'm delving deep into the lair of duct tape here, but what about completely filling the crevice with silicone? I fear that would eventually separate and lead to water infiltration so probably wouldn't solve the problem for long.

Only thing I can think of to permanently solve this would be to demolish the slab and have it re-poured level to the ground (which I don't have funds for at the moment). Part of me wonders if I'm making a bigger deal out of this than what I should be. It's been like that for nearly 30 years and there was 0 rot on any of the wood beneath the slab.
 
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Old 03-30-12, 06:45 PM
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I did note the condition of the OSB in your pix and it did seem to be fairly pristine. Of course plan B is the best one. Demo and repour. When you go to put the siding back on, flash under the siding (before you install the bottom pieces) and onto the concrete. This will allow any water that is sheeting off and under the siding to be redirected onto the slab, where it can drain safely away from wood parts. Now, if you want to fill the gap with anything, use Butyl Rubber. May not be cheap, but it won't fail like silicone will.
 
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Old 03-30-12, 08:51 PM
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I'm not real clear on what you're doing... whether the foil sheathing is staying or getting overlayed with OSB or what. Also not clear on whether or not this concrete is on a footing (impervious to the rise and fall of expansive soils and/or frost) or if it's got movement.

But if I was doing it, (assuming the concrete is on a solid footing below frost) I'd run a bead of sealant (such as Sonneborn NP1) on the cement, then install an L-flashing down into the sealant and against the sheathing, so that the gap is covered and sealed. Your weather resistive barrier (housewrap) would overlap the top of this flashing. Then i'd install the PVC band board on top of that, and probably seal the bottom edge to the flashing just to hide any ugly gaps. More flashing on top of the band board, and then the siding over that.
 
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Old 03-31-12, 12:06 PM
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Originally Posted by XSleeper View Post
I'm not real clear on what you're doing... whether the foil sheathing is staying or getting overlayed with OSB or what. Also not clear on whether or not this concrete is on a footing (impervious to the rise and fall of expansive soils and/or frost) or if it's got movement.
I'm removing the foil faced foam and then building out the wall with:
1/2" OSB Sheathing
1/2" XPS Foam
House Wrap

Along the bottom of the wall, I'm using 1x6" PVC trim for a band board and then running up the wall with hardiplank. The slab is directly on ground. Here is a different picture:
https://picasaweb.google.com/lh/phot...eat=directlink
 
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Old 04-06-12, 08:34 AM
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Sheathing

I see my house has the black almost like cardboard sheating with vinyl siding over it. What type of sheathing is this and whats your opinion? Thanks.
 
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Old 04-06-12, 04:03 PM
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Fishin,

its always best to start your own thread when asking a new question. That being said...

Your black sheathing is probably asphalt impregnated sheathing, some call it fiber sheathing, celotex sheathing, buffalo board etc. Not sure what kind of opinion you want. It was used for years and works fine. But its not plywood, so you can't exactly put a nail into it just anywhere and expect it to hold.
 
 

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