Rotten rim blocking Repair

[artbuc]

19 yr old home with natural stone veneer wall. Mason covered OSB sheathing with tar paper and laid mortar & stone tight against tar paper and did not install any drain/vent holes at bottom of wall. Water leaked through hole in the mortar and apparently collected on the top of the stone wall footer and was wicked up into the OSB and eventually rotted through the rim blocking. I discovered this when I was removing insulation to do some electrical work. I removed the rim blocking which was a bear because it had been properly toenailed during construction. Fortunately only the center of the rim blocking was bad and the joist ends themselves are solid. The bottom 8-10" of OSB is disintegrated.

What is the best way to repair this from the basement? I can't replace the sheathing but do I need to do something else to accomplish what the sheathing was doing? I was going to create somewhat of a moisture barrier with tar paper and then install new rim blocks. I want to cut off the corners of the rim block to allow the inside of the stone wall to breath into the basement although I don't know if this is acceptable. I could drill some vent holes in the bottom of the stone wall from the outside but it will be easier to let the wall "vent" into the basement. Of course by doing this I may have a problem with moisture condensing on the unsealed, cold rim blocking.

Do I have to fasten the new rim blocking or can I just drive them in place with an interference fit? I have read where rim blocking does 3 things: keeps joists from rolling over, transmits vertical load from house to foundation and helps lateral load by nailing floor into rim blocking. An interference fit will accomplish the first two, but not the lateral load.

What a mess! Thanks in advance for your help.

[Richard A Hetzel]

I don't believe an acceptable repair can be accomplished from inside. Among other issues, you'll be inviting water into your basement. You won't want to hear this, but the stone veneer should be removed, at least enough of it to be able to replace the rotted sheathing. That can possibly be done section by section, just high enough to gat access to the rotted sheathing, without demolishing the entire wall. More important, a base flashing needs to be installed, and weep holes provided. None of that can be done from inside.

[artbuc]

I don't believe an acceptable repair can be accomplished from inside. Among other issues, you'll be inviting water into your basement. You won't want to hear this, but the stone veneer should be removed, at least enough of it to be able to replace the rotted sheathing. That can possibly be done section by section, just high enough to gat access to the rotted sheathing, without demolishing the entire wall. More important, a base flashing needs to be installed, and weep holes provided. None of that can be done from inside.


Thanks Richard. I have considered your approach. In fact I may just tear down the whole wall and have it redone with man-made stone.

Can you point me to a reference that shows the base flashing and weep hole details?

Water infiltration aside, is the missing 8-10" of sheathing a structural issue? Are unfastened rim blocks a structural issue?

[Richard A Hetzel]

Without an air gap behind the stone, yes, water could be an issue, unless you carefully splice in some felt, under the existing and over the base flashing. If you work from outside, you should be able to fasten the rim joist repairs properly.

Here is a detail of basic base flashing...ideally there would be a one-inch space between the stone and the sheathing, so that water will run down behind the stone onto the base flashing, and exit through the weep holes, but you don't have room for that.
http://www2.snapfish.com/slideshow/AlbumID=278260793/PictureID=6809895164/a=122549428_122549428/t_=122549428

Neoprene stick-on sheet is good for the base flashing, and open vertical mortar joints in the stone will serve as weep holes.

[artbuc]

Without an air gap behind the stone, yes, water could be an issue, unless you carefully splice in some felt, under the existing and over the base flashing. If you work from outside, you should be able to fasten the rim joist repairs properly.

Here is a detail of basic base flashing...ideally there would be a one-inch space between the stone and the sheathing, so that water will run down behind the stone onto the base flashing, and exit through the weep holes, but you don't have room for that.
http://www2.snapfish.com/slideshow/AlbumID=278260793/PictureID=6809895164/a=122549428_122549428/t_=122549428

Neoprene stick-on sheet is good for the base flashing, and open vertical mortar joints in the stone will serve as weep holes.

I know that brick and stone veneer walls are supposed to have a 1" or so air gap for venting. However, the way my wall was constructed is quite typical for my area (SE PA). I guess the uneven nature/weight of natural stone makes it almost impossible to build it 1" away from the sheathing. Also, I think there are enough voids between the stone/mortar and the sheathing that the wall does breath and any leaks will eventually find their way down to the top of the footer or into the top of a window if it isn't properly flashed. My problem was no weep holes allowing water to collect and eventually breech the tar paper and wick up into the OSB.

[Richard A Hetzel]

Tha air gap isn't so much for venting as it is to prevent exactly what happened in your wall...rotted sheathing and structrural decay. The gap ensures that water which penetrates the stone (and much stonework is quite porous) will run down the back of the stone to the flashing and weep holes below. The felt, or house wrap, or whatever covers the sheathing, is a secondary water barrier, not a primary one.

It's a difficult chore to retrofit proper flashing. Removing all the stone, much as you may not want to, may be the best long-term idea. Then you can incorporate things like mortar guards (google that) on the flashing. If your foundation seems too narrow to permit stone with an inch of space behind it, all is not lost. It may be possible to vverhang the stone an inch to gain that space. Depends how deep your foundation shelf is. Or, maybe, if you replace the stone, you can find a thinner stone.

[artbuc]

Tha air gap isn't so much for venting as it is to prevent exactly what happened in your wall...rotted sheathing and structrural decay. The gap ensures that water which penetrates the stone (and much stonework is quite porous) will run down the back of the stone to the flashing and weep holes below. The felt, or house wrap, or whatever covers the sheathing, is a secondary water barrier, not a primary one.

It's a difficult chore to retrofit proper flashing. Removing all the stone, much as you may not want to, may be the best long-term idea. Then you can incorporate things like mortar guards (google that) on the flashing. If your foundation seems too narrow to permit stone with an inch of space behind it, all is not lost. It may be possible to vverhang the stone an inch to gain that space. Depends how deep your foundation shelf is. Or, maybe, if you replace the stone, you can find a thinner stone.

Thanks Ricchrd, again! What I find amazing is that there are hundreds, if not thousands, of houses in our area with stone veneer walls layed-up tight against the tar paper. New housing construction was booming in this area before the financial meltdown and I would often stop and ask the masons about this issue as they were building the stone wall. They all told me exactly the same thing. It is not practical to build a natural stone wall with an air gap between the wall and the sheathing. Go figure!

[Richard A Hetzel]

Yeah, I know, and there are still hundreds of insulation installers out there installing insulation upside down in crawl spaces, because that's the way they've been doing it for 25 years. The inherent fallacy in your comment is the assumption that the guy doing the work knows all the deisgn issues related to his work. The truth is that those who do are rare, and this forum is lucky to have a few of the rare ones. The construction industry is fraught with the equivalent of old-wives tales, and you've run into one of them. There will be some in every trade. The best at their trade will be the ones who know the design issues as well as the hands-on how-to-do-it, Chances are that a developer will not be hiring the best. What is the saying? There is nothing that someone can not do less well for less money, and those who consider price alone are this man's lawful prey.