Laying roofing felt over wet OSB?

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Old 09-26-16, 07:06 AM
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Laying roofing felt over wet OSB?

Hi everyone. I need an opinion. I've been frantically trying to finish building a small 8x12 "shed", before the rains came. I failed. I worked all day yesterday installing the OSB roof sheathing, in hopes of getting the roofing felt on before it started raining. I failed. It poured last night, leaving the OSB drenched. Unfortunately, more rain is heading this way for the next FOUR days. I have a little break in the weather today, that I could use to lay the felt. But..I'm hesitant, as the OSB is soaked. It seems like the felt would trap the moisture in the OSB. On the other hand..4 days of rain may ruin the OSB.

What would you do? Lay the felt over wet OSB, or let the rain continue soaking it? I need to get out there fast if I'm going to do it though. So, if anyone sees this, I'd appreciate an opinion. Thanks
 
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Old 09-26-16, 07:18 AM
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If the OSB is soaked it's already ruined, covering it now would be a big mistake. Since your only dealing with 5 or 6 sheets you should plan on changing all of it after the rain. You might want to invest in a plastic tarp large enough to cover the entire area of the roof and cover the roof area every time your not working on it until you get the shingles on.
 
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Old 09-26-16, 07:58 AM
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Hi Ron53!! Hey, thanks for the quick reply. Oh man. Perhaps I was a little too descriptive.
Yes, it got wet, but it's not completely drenched, as in...dripping from the inside face. I've had OSB get wet like this before, and then cut it. It's dry pretty much inside. My concern was trapping the moisture.
Ok, plastic it is. I've got some 7 mil black visqueen. I'll wait out the rain, and let it dry before laying the felt and shingles. I really don't think it's ruined. At least..hope it's not. I mean, how can you tell? It did rain hard for about 20 minutes last night. And last week, it rained on the OSB flooring. It dried in a day. But that's 3/4". The roof sheathing is only 7/16". Btw, this isn't a "typical" shed. I designed it for my wife's "ebay" studio and the roof is not a typical roof. It's 5/12 pitch, and took 6 sheets to sheath. I can't afford new sheathing either. Besides, it's nailed every 4" with #6 galvanized. That would be a nightmare to remove. At least for me. This roof was hard enough to sheath by myself. I even built a temporary "scaffolding" platform to make it safe getting on the roof from a ladder. I'm 70, and falling is NOT an option. As it is, the peak of the roof is 14'. Scary being that high. At least at my age. And removing it...un unh. Ain't gonna happen. Unless it's rotted. Here's a sketchup of the finished look. ..Name:  Woodbutchers Shed 1.jpg
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Anyway, thanks for the advice. There's a few pieces of cutoff on the ground. I'll cut a piece and see how wet it is. I'll let you know what I find. Thanks again.
 
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Old 09-26-16, 10:03 AM
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Best would be if you can tarp the shed until the threat of rain has passed. Then pull off the tarp so the sun can help thoroughly dry the OSB. Then go on with your tar paper and shingles. Not as good would be to put your roof on the wet OSB. If the interior of the shed is not finished and ventilated the OSB will eventually dry.
 
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Old 09-26-16, 01:52 PM
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Falling off a 14ft roof wouldn't feel real good at any age! You will see the OSB expanding or swelling if it got too wet. But it may be fine if it indeed didn't get "soaked". If you can get it covered in a way to allow as much air flow as possible between the visqueen and the roof it may dry out fine. I have always been a stickler about covering just about every project I do whenever practical, it's cheap insurance against the unknown.
 
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Old 09-26-16, 02:15 PM
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Most OSB has exterior glue and can stand a few wettings. Felt s are not vapor barriers so it will dry out even if you have to cover it.
 
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Old 09-30-16, 05:22 AM
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Hi everyone. Thanks for the replies. Well, I think I just over reacted out of fear of ruining all my work. It was fine. Sun came out and it dried within an hour. Got the entire roof sheathed with felt, all the drip edges on, and half the shingles on the upper roof yesterday. God, I'll never roof another building ever again. Just climbing the ladder up to the peak to nail the drip edge is a lesson in how age affects your fear of heights.

I built a platform to make transiting the ladder to the roof easier, and built a couple of level platforms to lay tools and shingles on. But the hardest thing is trying to keep from slipping off the roof when I'm nailing shingles. I screw down a 12' 2x4 about two rows above the row of shingles I'm working on, just to have something to sit on. But that won't help me once I get to the last 4 rows at the peak. Don't know what I'll do there, except probably stand on the lower roof and try and reach those rows. Even on that lower roof, I had to screw down a 2x4 to keep my feet from slipping. Man, I've roofed 4 houses in my life, but this is a 5/12 pitch and is the hardest I've ever done. Be glad when it's done. Ok, nuff bla bla. Back to work. Thanks again.
 
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Old 09-30-16, 05:29 AM
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Btw, what is the felt for, if it's not a vapor barrier? I did discover it still let's water through. So..what's the purpose?
 
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Old 09-30-16, 05:49 AM
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I had always heard that sap from wood was not good for shingles. I've also heard that the felt paper only needs to be used when shingles are going down directly on wood. It's not needed if putting on a second layer of shingles.

I've also heard that tar paper is not a vapor barrier. As the moisture passes up through the house and roof the vapor may condense on the bottom of the shingles forming liquid water. The tar paper is impervious to liquid water and prevents the droplets from wetting the wood.

Whichever reason or both is true I don't know for sure.
 
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Old 09-30-16, 05:59 AM
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did discover it still let's water through
How did you come up with that conclusion? I'm not a roofer but have done some diy roofing. 30 yrs ago I helped a friend build a large carport for his muscle car that he was restoring. He didn't have enough money for the roof so we laid 2 layers of tar paper [his idea] and left it that way for about 6 months at which time we addressed a few torn spots in the tar paper and shingled it. As far as I know the plywood stayed dry the entire time.
 
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Old 10-02-16, 07:14 AM
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How did you come up with that conclusion?
Because, after letting the OSB dry, I laid the felt, and installed half the shingles on the upper roof. Then it rained again. The felt got wet, and let water seep through it to the OSB. I pulled a portion of one course of felt back, and the OSB was damp. Perhaps it just felt damp from the previous rain before laying the felt.
 
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Old 10-02-16, 11:04 AM
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I suspect the OSB wasn't as dry as you thought and it was moisture that was 'sweating' out of the OSB.
 
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Old 10-10-16, 08:44 PM
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I'm late to the party on this thread, but just wanted to say that I like your Sketchup. I'm a Sketchup fan.
I totally understand your apprehension about heights. I did have a fall from a ladder the last week of April this year. I wasn't up terribly high, but I managed to break three ribs (one in two places) and broke my thumb. I developed a lung infection as a result of shallow breathing due to rib cage pain. The thumb still bothers me, but I'm back up on ladders again. I've watched a lot of ladder safety videos and am taking more time and precautions before I step onto a ladder now.
You may have finished your work by now, but, if you're really nervous about being up high, you may want to buy, rent, or borrow a harness.
 
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