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-   -   some frost on edges of roof sheeting in Attic above garage. Also am getting frost on roofing nails. (

Sebo20 01-16-2013 04:08 PM

some frost on edges of roof sheeting in Attic above garage. Also am getting frost on roofing nails.
I finished my attach garage ceiling a few years ago and insulated the ceiling also. It is a hip roof(if that matters). I heat the garage a few days a week with a protable heater. The garage door is insulated, but not the other two exterior walls. Two years ago, when it was cold outside. I noticed that the roofing nails above my garage would have frost on them. They would melt and refreeze causing littl rust spots/drops all over. I alsosaw some mold starting in attic above garage. It was then I found that there was no soffit vents around my garage area. They probably did not put them in when it was built since garage was ceiling was not finished. After noticing this, I put in 6 vents (4"x 14") on each of the three sides. Since it is a Hip roof, the soffit is only about 6". Last year was warm and I never saw any frost, so I thought the problem was ventilation and that I corrected it. I just had a new roof put on a few months ago and also installed a ridge vent. This year It has been colder and I noticed frost on the nails again and also some small areas of frost near edges of the roof. The home portion of my roof does not seem to have the same problem. Any ideas on what is causing this and what I should do?

joecaption 01-16-2013 04:37 PM

Got a picture?
Still not enough venting, attic area not air sealed, not enough insulation, soffit vents blocked with insulation.

Gary in WA 01-19-2013 10:40 PM

That part of the garage is not getting any excess heat from the house, so the moisture deposited on the nails-- frosts.

A propane heater will deposit moisture in the air as a by-product from combustion.
Sounds like your intake vents are way undersized; 6x14 is only 25 NFVA. What is the NFVA of the ridge vent? Bottom chart;

PS. Welcome to the forums!

OldNBroken 01-20-2013 09:36 AM

Am I reading you correctly? You say you installed 6 soffitt vents? I don't see any mention of ridge vents.

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