OSB sheathing and rot

[Robert Jones]

Does anyone know of a study or has studied, the time it takes for OSB sheathing to rot when there is a leak present. Size of the leak in this case, would be about the size of a pencil eraser.

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[mjr6550]

It the wood remained wet I think some deterioration could occur within months. If it dried fairly quickly it could take years.

[Jim Katen]

Sometimes, with a hole that small, water doesn't even seep into it. The surface tension, or whatever you call it, bridges the opening and doesn't leak.

That said, modern OSB is pretty amazing. For the last several years, I've worked on projects where the stuff is practically submerged in water for months at a time and, once it dries out, it hasn't even swollen, let alone rotted. I'm not sure what they're putting in it these days, but water just doesn't seem to faze it.

[inspector57]

Sometimes it is not the amount of water but the drying ability of the wall assembly. BSC has some good information in that regard.

I just saw a well known TV guy in Canada do a complete reclading of an entire 8 year old home due to rotting OSB all the while slamming the installers lack of attention to water proofing details.

My take was that the primary problem was trapping water between two vapor barriers with little chance for water or water vapor to get out of the wall.

Wall cladding will never be 100% water proof and if there is no provision to let the wall dry either to the inside or the outside you are asking for problem.

Regarding your roof hole, my guess is it would take years for rot to set in if that hole was over a well ventilated attic. No ventilation and my guess is that a few months would see major deterioration.

[John Kogel]

When I bought my present home, a T-lock shingle was blown off so that a strip of OSB was visible about 4" X 1/2". That's right, no underlay. I could see the grey OSB there and expected some damage. This is OSB from 1990.

When I stripped the roof I was surprised to see the only indication of the lost shingle was that narrow strip of weathered grey wood. No leak, no rot. It was ...miraculous!

[Jim Baird]

John, your exposed shingle was not a penetration.

I have heard a roofer say that he had fixed holes up to basketball size created by nail-hole leaks left by the original roofers' nailed-on cleats. Life span of typical roof would give you that time frame, yet I am sure every penetration is different.

[mjr6550]

Sometimes, with a hole that small, water doesn't even seep into it. The surface tension, or whatever you call it, bridges the opening and doesn't leak.

That said, modern OSB is pretty amazing. For the last several years, I've worked on projects where the stuff is practically submerged in water for months at a time and, once it dries out, it hasn't even swollen, let alone rotted. I'm not sure what they're putting in it these days, but water just doesn't seem to faze it.

Throw a piece of OSB on the ground and let it lay there for a couple years and it may not rot (if it dries out after being wet). Put the same piece in a wall behind badly installed stucco and you end up with mulch.

[kurt]

There's 4 grades of OSB. Talking about it all as one product isn't accurate.

What's the brand name of the stuff that's fully waterproof? I forget......wait...Advantech. That stuff is amazing. I did some tests several years back where I put the stuff in a bucket of water for a year; id didn't change dimension or degrade in any manner whatsoever.

I know that #1 goes to mush if you get it wet; it's the interior grade stuff that I occasionally see used as roof sheathing on cheap reroofs.

This reminds me I should start checking grade stamps more carefully.....