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Old 12-27-2011, 04:22 PM   #1
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Moisture in sheathing


What is the average moisture content (%) of roof sheathing in an attic?

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Old 12-27-2011, 05:03 PM   #2
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Moisture in sheathing


A most lumber is kiln dried, there shouldn't be any moisture.

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Old 12-27-2011, 06:04 PM   #3
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Moisture in sheathing


Right no my attic shows 57% humidity. Some days it is as low as 13%. So in theory yes, there could be moisture in it, but it should not hold it if the house attic space is well ventilated.
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Old 12-27-2011, 06:52 PM   #4
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Moisture in sheathing


If the sheeting is osb, as opposed to plywood, it is lightly sealed from moisture from the factory also.


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Old 12-27-2011, 07:08 PM   #5
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Moisture in sheathing


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If the sheeting is osb, as opposed to plywood, it is lightly sealed from moisture from the factory also.


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I was going to say, doesn't it have carnuba wax or the such on it, where as with ply unless it is outdoor, basically has nothing.
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Old 12-29-2011, 08:54 AM   #6
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Moisture in sheathing


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What is the average moisture content (%) of roof sheathing in an attic?
That would vary greatly with your location (which you have not provided). Moisture content in sheathing can vary from one side of the roof to the other depending on exposure to the sun, air flow within the attic, etc. A probing moisture meter will tell you. Relative humidity in air is different than percentage of moisture content in wood. RH in air can have an effect on moisture content in wood, but 57% RH is not going to give you 57% moisture content in sheathing, rafters, etc. Percentage of RH is temperature driven. There will always be a certain amount of latent moisture in the sheathing.
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Old 12-29-2011, 09:05 AM   #7
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Moisture in sheathing


My moisture meter is giving readings up to 15%. Is that high for sheathing in an attic?
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Old 12-30-2011, 07:35 AM   #8
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Moisture in sheathing


No. Roof sheathing can vary some because of miniscule amounts of condensation under the shingles. Sheathing probably runs 9-15% depending on your location. Processed materials like OSB or plywood tend to run slightly higher than solid wood because the glue will trap a slight amount of moisture in the wood fibers. Make sure your attic ventilation is working properly.
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Old 12-31-2011, 05:53 AM   #9
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Moisture in sheathing


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My moisture meter is giving readings up to 15%. Is that high for sheathing in an attic?
Wood with 15% moisture content is considered "dry" for all practical building purposes.

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