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moisture in attic


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I am considering replacing my roof. A metal roofing rep came to my house and inspected my attic areas. He used a meter to indicate moisture and in some cases his meter indicated that the mositure content in my attic insulation was high enough to promote mold growth. The moisture levels were attributed to the fact that I had installed platic wrapped fiberglass insulation. The high moisture was only found in one attic area which makes me believe that the insulation was not the cause as both sides have the added insulation. There are no indications of leaks in my attic, my roof asphalt shingles iare20 yrs old. The side with moisture has a bird nest that blocks in part the vent on the side of the house. The attic does not have a ridge vent but does have vent boxes below the ridge. Is there a criteria for measuring moisture content and at what level will mold become a problem?

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Daniel,

I "guessed" your question after the third sentence! What was the salesperson trying to demonstrate? What did he recommend for your attic spaces? New Insulation?

Mold requires moisture to grow. Some mold needs lots of moisture and some require very little. The demonstration was BS. Why do you want a metal roof? (I am curious only because of typical costs)

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It's not clear from your post where the insulation is installed.... under the roof deck? If so, the combination of the encapsulated insulation and the lack of ventilation in that area could indeed cause elevated moisture levels. I would not want readings much above 14% or so, and preferably less. The attic can gain some moisture by solar vapor drive thru the shingles, but the majority of it is probably percolating up from the living space below thru gaps, cracks, holes, etc. You want to keep the humidity in the attic well under control, mostly by air-sealing the attic floor, boxing any recessed lights, building an insulated cover over the attic hatch, etc., and you want at least the code-required ventilation levels, unless you opt for a completely sealed and conditioned attic.

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Well that's a real shocker to hear, David. I like to ping Inspectapedia once in a while and I had used this article to formulate my own rules of thumb. They basically suggest 45% is a safe area. I can only imagine the amount of ventilation needed to be under 14%! It would be great to get the feedback of more guys in here. If I'm giving too much room, I'd like to hear it from a few more sources.

http://www.inspectapedia.com/sickhouse/humidity1.htm

Thanks,

Grant

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Well that's a real shocker to hear, David. I like to ping Inspectapedia once in a while and I had used this article to formulate my own rules of thumb. They basically suggest 45% is a safe area. I can only imagine the amount of ventilation needed to be under 14%! It would be great to get the feedback of more guys in here. If I'm giving too much room, I'd like to hear it from a few more sources.

http://www.inspectapedia.com/sickhouse/humidity1.htm

Thanks,

Grant

Time of year and location.

If I were running 45-55% RH, with a 10 degree outdoor ambient, my attic would look like a mold factory. 45-55% RH with an outdoor ambient of 90 degrees and an attic temperature of 130 degrees is a different story.

You can't put all homes, in every location, in one neat tidy box.

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Hi,

I think we're confusing RH with moisture content in wood in these posts. 14%+ moisture content in wood and you're at the cusp of the potential for decay. Agreed, under 50% RH shoud keep it under control if the temp ranges in the attic are favorable for mold growth.

Right now, I wish it were 130°F in the friggin' attics. I stopped my office work to take a lunch break and saw on the news where it hit 103°F at JFK in New York. We went 272 days here before temps hit 75° here and it's gotten cool again. My office is on the shady side of the house on the basement level. Despite the fact it's a bright sunny day out, my office is downright cold. I've got the friggin' heat on down there cuz I don't feel like bundling up.

Saw an article the other day about folks up at the pass skiing.

This place is weird sometimes.

End of vitamin D deficiency rant.

ONE TEAM - ONE FIGHT!!!

Mike

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Thanks, Dok. I was starting to think I was losing it because I've never seen mold grow sub-freezing temps.

You have to take into consideration the sun heating up the roof in the daytime.

I've been in attics that have a lot of frost on the sheathing and nails. All you have to do is warm it up a bit and all the frost is now water. Do this for ten years or so.

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