Charles, a homeowner in Pennsylvania asked:
I have lived in my home since 1993 and never had a problem with mold in my attic. I just had my home re-roofed only to find something changed the ventilation. Original ridge vent was an 8.5" x 8' aluminum style and the new ridge vent is mesh with shingles over top. The front side of the roof faces N/W and is covered in mold whereas the back of the home facing S/E has zero mold. I am unsure of a remedy. Replace ridge vent or install a gable fan (humidistat - temperature). The gable fan would be 55' from other side of home and not sure how efficient it would be coupled with a ridge vent.
Our resident expert roofer, John Stout with Go Roof Tune Up™, had this to say in response:
This is an interesting observation about the change in ventilation. Proper ventilation is very important to balance attic air. You note that the vent was changed near the ridge. This indicates that the problem is the change of the eight-foot vent to ridge vent at the shingle trim. This is a good place to start to find and solve the problem.
The accepted ventilation ratio in the attic is one square foot of ventilation for each 300 square feet of attic floor space. This changes with different climate zones. The ratio could be as high as one square foot of ventilation per each 150 square feet of attic floor space. Check your climate zone. The vents need to be 50% high and 50% low. I suggest you verify the attic space. Verify the vent area. Verify the ½ high and ½ low formula.
If everything checks out, you could put a portable fan in the attic to see if it helps. Keep in mind that you must have enough ventilation for the exhaust.
I hope this information helps. It should be fairly easy to fix the problem. The tough thing is to identify what needs to be done. Enjoy the task.
Thank you very much for your note. Hope this information helps.
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