Often, they are. But it's been wet this month and they don't always track. At 2PM, the outside was 41F 41% DP In the attic, it was 47F 90% DPD That seems to be a problem.
But at 5PM, it's outside 36F 44% DP Attic is 46F 76% DP9
Other times the inside/attic dew points are about the same.
I've been using this site:
The 90% number is not good for mold growth. The 76% number ain't so bad. The attic is below freezing at night, so may be collecting moisture as ice crystals.
I don't have a historical log, but I haven't been alarmed in the past.
House is 47 years old ranch in Portland, Oregon. Two layers of asphalt shingles. Wasn't leaking when I put on the second layer.
The insulation is fiberglass. I expect it holds some moisture and there will be some delay in the humidity dropping as the outside humidity changes.
I called the roofer and asked about humidity in the attic and was told to email the data. The response basically ignored what I wrote and gave no answer.
There's a lot of insulation in the attic and I can only get at about half of it without messing up the insulation. I see no evidence of leakage around all the stuff sticking thru the roof and no evidence of water damage, but I can't see much of the wood on the inside of the roof.
Am I worrying too much? Or should I put on the rubber boots and trudge thru the insulation to get a better look.
What humidity should I expect to see in the attic?