# Proper way to repair exterior sheathing rot?



## dloomis (May 22, 2016)

Hi folks - thanks in advance for whatever advice you can provide. I'm in the middle of a patio project and need advice on how to properly repair water damage to the siding of my house.

I removed a 10-year old deck yesterday and found some sheathing rot behind the ledger board after I removed the waterproof membrane. It appears to be coming from an improperly flashed sliding patio door which also is getting replaced. The OSB flakes off quite easily and I could probably tunnel my way through with my finger if I pick long enough.

The OSB itself is quite thick (> 1") so I'm not sure if the entire section should get cut out or simply repaired. Please see the attached photos to see what I'm talking about.

Thanks again!


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## Daniel Holzman (Mar 10, 2009)

That looks like chip board, not OSB. Chip board is a poor material for sheathing, plywood is much better, and some types of OSB are OK. I would replace the damaged sheathing with plywood.


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## Millertyme (Apr 20, 2010)

Hmmm. Definitely looks like osb to me, which is the most commonly used sheathing for houses.


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## Bud9051 (Nov 11, 2015)

I agree with it probably being osb, but since you are replacing that slider it will be a much better job if you pull the surrounding siding, replace all damages sheathing, add house wrap and proper flashing, then the new door. Then re-install the siding if opening remained the same.
Note, you say greater than 1" thick, that is due to swelling from the moisture. Started at 1/2" most likely.
Also, if attaching a new ledger it REQUIRES extreme flashing. Others will have more on those details if needed.

Bud


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## dloomis (May 22, 2016)

Thanks for the feedback everyone. I'm getting someone out today to evaluate the situation and discuss options. I'll report back what he says, if nothing else but to close the loop on this thread.

P.S. The OSB is definitely an 1" thick all around, at least for the 18" that is exposed in the picture. Is it possible that they reenforced this part of the house in order to properly secure the deck ledger? You can see the holes where the ledger bolts used to be...and I can't imagine properly securing it on anything flimsier. But I'm not in the biz so I could have it wrong of course.


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## joecaption (Nov 30, 2011)

Here's your chance to now rebuild that deck and and make it free standing so there's 0 chance of it causing wall issues.
Was there any support under that threshold against the outside wall?
https://www.google.com/search?q=pat...MAhXKbz4KHYT2AlwQsAQILw#imgrc=KSohi2srZ2QF7M:


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## carpdad (Oct 11, 2010)

1. No need to replace the sheathing (does not matter what it is) if you're putting the deck back. Ledger needs 2x frame, not the sheathing. 

2. Ways that water WILL get under the siding and the door and rot everything again: the slide door, probable lack of flashing for the door, no pan for the door, door bottom is trough type bypass track (will hold water and possibly drain through the screw holes or corner joints). The top of the door probably does not have a rain cap (name?). The siding has J channels around the door. If you look at the top channel, it is inverted into a trough. Even if you have an overhanging roof, some rain will get into it and drain to the sides. If you bend the channel at the top corners, you will see that they are jointed and will see big gaps. Some water will drain through here. Rest of the water will flow down and drain under the siding and on your siding.

Sorry for the nightmare I gave you. You are probably wishing you never asked - ignorance is bliss. Now that you know, only fix is remove the siding, remove the door and probably flash, install, tape the joints, use good caulk, etc, and making sure plane of drainage goes past the organic material.
Peel and stick membrane is good choice (don't use butyl) for drainage. Don't use metal flashing if touching pt lumber. All flashing and drainage plane overlaps the course below - don't depend on tape for this unless it is eternabond tape.
All work here is common sense and diy-able, by the way.


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## dloomis (May 22, 2016)

This is super helpful...thanks joe and carp. I neglected to mention that the deck is NOT going back up. I'm having a patio put in, and obviously in it's place at the door will be a landing and stairs. I'm not 100% if that changes anything from a waterproofing standpoint but I thought I'd throw that in there.

Like I mentioned earlier in the thread, the slider is also getting replaced a bit later, and since the patio guy will be on the hook to repair this damage...I'm inclinded to remove the slider NOW, repair it properly, and put something up temporarily until we can get the new patio french doors put in about a month from now.

P.S. What do most folks put up to cover that 18" gap where the the ledger used to be? New vinyl siding won't match, and I'm not sure another ledger will look good. Decorative flashing maybe?

PSS. The old ledger WAS attached directly to the OSB...you can see the holes in the picture. That said, the OSB was very thick (> 1") which might have been OK from a code standpoint about 10 years ago. There was minimal waterproofing under the threshold, if any.


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## dloomis (May 22, 2016)

Update:

I got dirty and took a pic from inside of the crawlspace. The 2nd is from another angle on the outside to show the thickness of the OSB.

My house has 18" engineered I-joists running adjacent up to the backside of that rotting OSB. There is no additional 2x framing at this level. The OSB itself is a whopping 1.5" thick, which is either because a) it has to be in order to securely bolt the ledger board to it (remember, there is no 2x framing there), or b) the I-joist construction in general requires it...or c) both.

My question is: do I need to replace, repair, or just dry out and cover it up with better waterproofing? There is no deck getting reattached so I'm not sure what is required from a structural standpoint.

The attached pictures should hopefully visualize what's going on.


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## dloomis (May 22, 2016)

And now that I've done some more research - it's clear to me that the OSB is basically a rim joist that is spanning the entire backside of my house. The sides are framed with 2x4 and standard sheathing.


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## Gary in WA (Mar 11, 2009)

The rim board is usually 1-1/4" and of OSB. OSB swells after water contact and does not regain original thickness. Yours may have started at that thickness; regardless- you will need to add flashing behind the WRB (hopefully) under the vinyl and a trim board running horizontally to break the added new siding below appearance difference. 

Gary


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