I was asked to look at an attic that has very visible mold and much moisture on the entire underside of the sheathing. Any ideas?

Asked by Doug Storey
Bolton, MA

It is a cold attic in a 1970s era home with soffit vents and two gable end vents but no ridge vent. I know of course it needs a ridge vent added. It has batt insulation in the ceiling bay. It does have insulated HVAC ductwork and a furnace in the space but no sign of leakage. It has two bath vents ducted through the gables with flexible duct vent pipe. Moisture is very visable and condensing to the point where is drips down the wall and leaves streaks on the walls in the floor below. Also in one bathroom the tile has falled off the wall. Moisiture is condensing on windows in the house as well. I know the lack of ridge vent is a problem but I wonder if the roof is failing as well. There is just so much moisture. 


Sean Lintow Sr

Answered by Sean Lintow Sr

Naperville, IL

SLS Construction & Building Solutions

March 5, 2013

I know this might throw you for a loop but the lack of a ridge vent is not the issue, especially as you have gable vents.

The issue is excess moisture in the attic which requires you to find the source of it and manage it. Primarily you need to make sure your attic is separated from the other levels by proper air sealing and that all your dryer, bath and oven vents actually vent outside and not in the attic.

The next item is managing the moisture you generate, so once everything is vented properly:

  • make sure you use those exhaust fans,
  • consider lowering the temperature somewhat, and
  • if you have a ton of indoor plants or a ventless heater you are going to have reconsider them.

Once you have done all this (and your attic starts drying out), you may also want to look at how much insulation you have and make sure it is installed properly.


For more information:

See my blog post entitled "Ice Dams, Icicles, and Attic Condensation." 

Tagged In: attic insulation, air sealing

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