Protect ground level sheathing & bottom plate.

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KeepTryin
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Protect ground level sheathing & bottom plate.

Post by KeepTryin » Tue May 15, 2018 8:37 pm

Hello,

I know it's not very smart construction, but it's part of the house my wife and I bought over 25 years ago.
The section I'm working on now is slab on grade. It's actually a converted garage. Here's a look at what I'm dealing with:
DSCN3016.JPG
Exterior wall touches driveway.
DSCN3016.JPG (101.67 KiB) Viewed 88 times
As I get ready to replace the sheathing and the siding, I'm looking for ways to protect the bottom plate and the bottom of the sheathing as much as possible.
My current plan is to use pressure treated 1/2" sheathing for the bottom 18 - 24" of the wall. I'm using a 1x6 PVC band-board to cover the bottom-most portion of the wall (I've done that in other areas that I've completed). In the area I've uncovered so far, the bottom plate, surprisingly, seems solid. But, I know from a hack repair I made several years ago, the plate at one of the corners is very spongy.

I've thought about covering the plate with metal flashing (sandwiched between the PT sheathing and the plate). But, I know that I can't have aluminum flashing in contact with pressure treated wood. I've also thought about using ice & water shield over the PT plywood. I'm concerned, however, if I apply a non-breathable membrane over the sheathing, the sheathing, and by transfer, the bottom plate have no way to dry out.

What are your suggestions for how I can make the best of a less than ideal situation?

Thanks in advance for your insights.


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A. Spruce
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Re: Protect ground level sheathing & bottom plate.

Post by A. Spruce » Tue May 15, 2018 10:33 pm

I think you're on the right track with the pressure treated materials for the plate and sheathing. I think that using IWS to protect the plate and lower section of wall will be fine, because water shouldn't be getting into there anyway, it's certainly going to seal that area from water backsplashing off the driveway, which is what damaged the OSB sheathing to begin with, and why I never use OSB for any reason what-so-ever.
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Shannon
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Re: Protect ground level sheathing & bottom plate.

Post by Shannon » Wed May 16, 2018 7:10 am

Yup I would use a membrane on the exterior of the new PT plywood and then use Big Stretch caulking to seal the bottom joint between the membrane and the concrete. If you are replacing the bottom plate as well then you can use PT lumber there . Be sure to use the proper ACQ fasteners into the PT materials.
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KeepTryin
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Re: Protect ground level sheathing & bottom plate.

Post by KeepTryin » Wed May 16, 2018 9:27 am

Thank you very much @A.Spruce and @Shannon.
@A.Spruce, I agree. I'm not a fan of OSB at all. The original part of the house was all Homasote, which IMO is even worse than OSB. I've replaced all of that with plywood, now I'm on to this addition and part of it is OSB and I will be replacing that as well. My 2 car garage is, unfortunately all OSB, but it's the newest addition to the house, so it's still in pretty good shape. With limited time and budget, I think the garage will need to remain OSB--Although, I might replace the bottom 18-24" with PT ply.

In addition to concern about splash from the driveway, I was also concerned about "wicking" moisture that would have no way to dry out if I used a membrane that didn't breathe.

@Shannon, thank you for your suggestion of using Big Stretch. I wouldn't have thought of using it to fill a gap between asphalt and concrete. I was thinking either Sika, or BlackJack Speedfill, or one of those asphalt "ropes" you melt in place.

Best regards.

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A. Spruce
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Re: Protect ground level sheathing & bottom plate.

Post by A. Spruce » Wed May 16, 2018 10:34 am

KeepTryin wrote:
Wed May 16, 2018 9:27 am

In addition to concern about splash from the driveway, I was also concerned about "wicking" moisture that would have no way to dry out if I used a membrane that didn't breathe.
With the membrane in place, there could be no wicking, other than by the siding, which would be minimal and would dry out. With the siding, whatever you use, if you paint the bottom edge and back of the first course, you will go a long way to preventing the wicking.
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KeepTryin
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Re: Protect ground level sheathing & bottom plate.

Post by KeepTryin » Wed May 16, 2018 12:39 pm

Thanks again @A.Spruce.
My bottom-most course of siding will be the PVC band-board. That won't wick moisture at all.
The bottom edge of the plywood sheathing, even though it is PT, "could" wick moisture though couldn't it?
Also, the existing bottom plate has no barrier between it and the concrete slab that it sits on. Doesn't that wick moisture from the concrete?

I appreciate your time and thoughts.

Best regards.

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A. Spruce
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Re: Protect ground level sheathing & bottom plate.

Post by A. Spruce » Wed May 16, 2018 1:11 pm

KeepTryin wrote:
Wed May 16, 2018 12:39 pm
Thanks again @A.Spruce.
My bottom-most course of siding will be the PVC band-board. That won't wick moisture at all.
The bottom edge of the plywood sheathing, even though it is PT, "could" wick moisture though couldn't it?
Also, the existing bottom plate has no barrier between it and the concrete slab that it sits on. Doesn't that wick moisture from the concrete?

I appreciate your time and thoughts.

Best regards.
If you're replacing the plate, the I&W would go under the plate and up the face of the sheathing 12" - 24", thus eliminating the chance of wicking.

If you're not replacing the plate, then applying some sort of sealant to it before you install the sheathing would be a good idea. Something along the lines of Black Jack roof sealant would suffice. Then putting the I&W on the lower portion of the wall, you could wrap the bottom edge of the sheathing, say 2" up the back, around the bottom and up the face by 12" - 24", again, if water can't get to it, then there won't be any issues.

The plate on the concrete is going to wick some moisture, but it should only be minimal at at worst, unless water is able to pool against the plate. From the pix you posted, the driveway is a couple of inches lower than the wall plate, so that you might be getting some splash, but no standing water against that wall. I think that the root of your problem here is that splash getting on the OSB that was slightly exposed below the siding, even though you couldn't see it, it was in direct line of splash, hence the damage to the bottom edge.

I'm a bit concerned with your PVC trim board, if you're installing this on the wall before the siding, what is keeping water from getting in behind it? Another reason to run the I&W up the wall a ways. Are you going back with the shake siding or something else?
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Re: Protect ground level sheathing & bottom plate.

Post by KeepTryin » Wed May 16, 2018 1:51 pm

Thanks once again for your ideas @A.Spruce.
I have Z-flash over top of the PVC.
The new siding is Hardie plank. The PVC gives me the clearance above grade that Hardie requires.

I think you're right about splash being at the root of the problem. Also, note that I'm in Western New York where we get more than our share of snow in winter. Oftentimes the snow sits up against the siding and eventually melts. Another thing that isn't evident in the picture is that there was backer board (similar to Homasote) behind the cedar shakes. That backer board held onto moisture.

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A. Spruce
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Re: Protect ground level sheathing & bottom plate.

Post by A. Spruce » Wed May 16, 2018 2:13 pm

I would then suggest that the I&W be installed above your average snow line.
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Re: Protect ground level sheathing & bottom plate.

Post by Shannon » Wed May 16, 2018 5:15 pm

Ya thats where I figured you would place the Big Stretch, sealing the joint between the membrane on the wall and the concrete . This will help seal standing moisture out of the bottom edge of plywood and plate.
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KeepTryin
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Re: Protect ground level sheathing & bottom plate.

Post by KeepTryin » Thu May 17, 2018 7:37 am

Thank you @A.Spruce and @Shannon.
I have my materials list ready now.

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