How do you tell if roof sheathing really needs replacement?

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AcidWater

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Dunno if this is really an appropriate question, but people here seem to cover lots of trades.

Lookin in the attic, I can see some areas are black. Mostly close to the bottom over the eaves (2' overhang). Mostly black mold is harmless wrt health. And whatever problem caused it might have ended 25-30 years ago when I put a 2nd layer of shingles over the first. Or not, if it condensation from inside.

Also see stains around nails -- Hmm, should see if only half have stains (1st vs 2nd layer)

Today in sub freezing I can see some frost down on the soffet boards, and here & there frost on a nail. But not on the sheathing.

So when I eventually replace the roof & the sheathing is exposed, what is the accepted test for replacing areas of sheathing? Black on top & bottom? Hitting it with a heavy hammer to see if it breaks through?

Also trying to figure out cost per square for the various aspects of a roofing job
-- removal of 2 layers
-- disposal costs for 2 layers
-- installing a ridge vent
 

Dana

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If it's punky enough to poke an ice-pick through, it's toast and needs replacing. Short of that it's a judgment call- it it flexes too freely in spots when walking on the roof even though it's supporting your weight it's worth considering "early retirement" rather than roofing over it and having it cave-in on a roof walker before the shingles are shot.

If you fix all the air leaks from conditioned space bringing humid winter air into a cold attic all winter to be taken in as adsorbed moisture into the roof deck, the roof deck will last pretty much forever.
 

Dj2

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"And whatever problem caused it might have ended 25-30 years ago when I put a 2nd layer of shingles over the first. Or not, if it condensation from inside."

Question: Did you put tar paper before you put the second layer of shingles?

When you check a roof deck, you look at colors last. You walk on it, you check the spacing between rafters, you determine the thickness and if is it plywood or OSB. These are the things an experienced roofer can tell you, after the deck is cleared of all shingles. I replaced a roof last summer, which had a deck made of 1x6 planks, so you see there are various types of decks.

A word about pricing: All you need to do is call a few local roofers and get at least 3 estimates (broken down as you wish...but many roofers will not give you piece pricing though). Weather conditions affect prices. Demand for roofers affects the price. Your roofing choice affect the price. We can't give an estimate, we live in a different area.
 

Jadnashua

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The next reroof pretty much requires a tearoff...two layers is pretty much the max. The nails will rust if there's a leak from above, but as mentioned, it's probably more a factor of air leaks into the attic bringing moist air that condenses (or freezes, as you saw). A leak might get an icicle, humidity usually ends up in frost.

From the top, on a typical asphalt roof, loss of most of the granules and/or curling or cracking of the shingles means it's past time to replace. If there's a lot of moss, that will shorten the life of the roof...it might be worth trying to remove it.

If you don't have decent soffit vents or they're clogged up, a ridge vent may not buy you as much as it normally would.
 

Dana

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The nails will also rust from wintertime condensation when there humid air leaking in from an improperly sealed ceiling under the insulation layer. That's also a primary factor with the mold on the roof deck.

With soffit to ridge venting the free area of the soffit vents needs to be bigger than that of the ridge vent, to keep the pressure differential between the conditioned ceiling and attic about the same. If the ridge vent area is larger than the soffit area it adds some stack effect drive to pull conditioned air through the leaky ceiling into the attic in winter.
 

Cacher_Chick

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If the wood from the roof deck is solid, there are ways to treat the mold, which can be an entirely different issue.
 

AlexWilliams

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I had to exchange the roof completely because there was humidity from an improperly sealed ceiling under the insulation layer, which caused rusting and a lot of damage. This is indeed a headache, and it made a hole in my wallet, but at least I know it's professionally done, so I have nothing to worry about. After the roof was almost done, I opted for rhino roofing Jacksonville because the company was recommended by many of my family members, and I think they did a great job at coating the roof with a self-priming ceramic elastomeric roof coating that is supposed to provide ample protection for the roofing system. This time I didn't rely on myself and worked with a professional company because I didn't want to have roof issues for another 15 years at least.
 
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Fitter30

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Architectural shingles at least in my area are the same cost as regular shingles because the layout is easier and faster.
 
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