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Roofing/Attic moisture after new roof installation

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Question
We live in the Midwest where we can have very hot summers and can also have very cold winters with large fluctuations of temperatures.  Our house is 13 years old, and we never had any issues with leaks or attic moisture.  We had hail damage to our roof, and had our roof replaced in the fall 2012. Our old roof was a 3 tab asphalt roof put on by the original builder of the house, and we were replacing it with a newer and heavier dimensional roof. The old roof was scraped off, new felt was laid, and new Owens Corning OakRidge dimensional shingles were laid down.  No other changes were made to the house prior to the or after the new roof being laid down.  

In January, we noticed that the drywall in one bedroom appeared to be wet as well as on the other side of the wall in the hallway, so I inspected the attic to see where this moisture was coming from.  When I got into the attic, I seen that on the North side of the house that the inside roof was frosted over with a sheet of ice as well as a layer of frost on the top of the blown in insulation, and it appears that when the temperature went over 32 degrees that this ice was thawing and dripping down.  I looked all over the place and never found any signs of a leak, and all the moisture inside the house appeared to isolate to the areas of the ceilings along the walls of the house along what appeared to be mold.  It took us about two weeks to thaw and dry out the attic, and we turned on the attic fan adjusting the humidity setting.  We normally don’t run the attic fan in the winter as it was installed to keep the heat down in the summer when we built the house, and never had any issues with moisture in the attic the proceeding years since we built the house.  The attic fan ran so much over two weeks that it burnt itself out and had to be replaced.  As time has gone on, we are now seeing moisture and mold in other rooms and locations including the inside of the roof decking, on top of the blown in insulation, and on the ceiling near the walls and in the corners of three rooms all associated with the outside facing walls.

We have had the original roofer out a couple of times for both the moisture and a vent that was not installed, and on the first time out the worker blamed it on a vent that had the a slight separation in the duct which appears to have been like that for a very long time.  We continued to have more moisture and mold appear so, we had the original roofer come out  again to look, and they acknowledged the missing vent as well as coming back with an IR scan to see if they could identify the source of the moisture.  The original roofer came back to replace the vent, but has never made an attempt to see where the moisture was coming from in the attic.  

We had a different roofer come out to look at the roof to see double check the integrity of the work performed, and this other roofer related that he could not find anything wrong with the roof installation.  I was asked what type of roof was replaced, and I related that it was an asphalt 3 tab roof.  This other roofer related to me that he has seen newer and heavier shingled roofs cause more moisture in the attic because of the heating and cooling differences from an old roof.  

I have read that “cool roofs” in northern climates have presented problems with the dissipation of moisture because it doesn’t heat up in the winter like older material which affects humidity in the attic as well as causing ice dams as snow doesn’t melt as fast.  I noticed that the snow on the roof with the new roof on the North side of the house doesn’t melt like it used to as well as now having high humidity in the attic.  

Would a newer and heavier shingle cause a difference in the humidity, or would there be something else that could have happened during the process of installing the new roof since there were zero problems with attic moisture before we had a new roof put on, and now we have continual problems with attic moisture.  Should any considerations have been made by the roofer as to ventilation with the install of a newer and heavier roof?  Could there be something else that has taken place that is not readily obvious?

Answer
Firstly, does your roof have adequate ventilation?
An attic normally follows the 1:300 ratio for ventilation.
Using the top floor of your home (i.e. 1,200 square feet) divide by 300 equals 4 square feet of ventilation shared between the roof and the soffits.
So two square feet (288 square inches) each would equal approximately 5 roof vents since a vent is normally 56 square inches.
Ice and snow build-up is normally the indication of lack of venting.
The shingle manufacturer wants it correct so the attic is always equal to ambient temperature. If not the shingles will fail as thye will fry like an egg on a hot sidewalk.

The code wants it to remove moisture from the attic space.
Possibly the soffits are blocked with batt insulation so best to check there too.
The two areas that generate the most moisture is the bathroom and the kitchen.
Check to make sure your bathroom exhaust fan is functioning and venting to the outside.
Sorry not aware of any issue with changing the shingle weight or style in regards to contributing to attic problems.
Hope this is a start.

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D. John Henderson

Expertise

My 33 years in the building science business has involved air barriers, waterproofing, and flat & steep slope roofing systems.

Experience

My roofing encompasses commercial systems (BUR, mod-bit, single-ply) and residential applications (asphalt shingles, cedar shingles, slate and metal. I am cognizant of code stipulations in regards to FM and UL for commercial roofs.

Education/Credentials
Attended numerous courses offerd by Roof Consultants Institute, Roofing Industry Educational Institute, Factory Mutual Research Corporation, University of Wisconsin, and BURSI. Lectured for RCI and mentored at a local university for a Building Science Certificate.

Past/Present Clients
Government, commercial businesses such as The GAP, hospitals, school boards as a roof designer.

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