Who can guess, Moisture in attic source?

[twoply]

Hello all,
I have a resident/ friend that has this situation going on.

We are in Ohio. The roof's snow is melted from an area that spans from the ridge peak, down the rafter about 4 feet and all the across the whole roof. Both sides of the ridge. Other than that, the rest of the house has about 10 inches evenly covering it.

The underside of the roof sheathing is evenly moist under this area, almost like a dew glazing.

There is no mold growth of any kind.

The insulation in the attic is new and properly installed. Ridge vent and soffit venting are good. Baffles are properly installed. No icicles.

The furnace and HWT vent up through this space and terminate outside.

The only thing I can think of is that the vent from the furnace/ HWT is leaking in the attic and causing that snow to melt and supply moisture to the attic.

Thoughts?

I tried to upload a photo, but I'm not tech savy at all.

 

[SCBO1]

Make sure the dryer is not vented into the attic and bath fans should vent to the outside not the attic.

Also, check for loose flue connection.

Double check the baffles, may be full of blow-in insulation clogging the soffit vents.

 

[cda]

What room/s of the house is under this area??

And I guess no vaulted ceilings in this area?


Sun hits this area only?

 

[jeffc]

A major cause of moisture in attics is leaky can lights (or just air leakage in general). The old can lights were notoriously leaky to help dissipate heat. The warm moisture laden air raises up into the attic, cools and deposits the excess moisture onto the roof structure. As for the snow melting, the ridge vent could be funneling all the warm air escaping from the house through the ridge vent and contributing to the snowmelt.

 

[Sleepy]

Like Pcinspector1 I would suspect dryer or bath vents, or kitchen hood vents ending in the attic. Or can lights, or some other opening to the heated space. If the snow on the roof is melting I would think that plugged soffit or ridge vents wouldn't be the sole cause, maybe contributing, but there must be a source of warm, moist air.

 

[Sifu]

If I understand, the top 4' is moist at the surface of the sheathing?? If so, assuming there are no other moisture producing conditions in the attic such as bath fans, dryers etc I would guess this: moist air is being drawn in through the soffit vent, moving along the intended path up the inside slope of the roof. Since snow can actually be an insulator the 10" of snow on the roof is insulating the sheathing and it may be a smidge warmer than the top 4' of the roof, which doesn't have the snow/insulator and the moisture is condensing on that cooler surface (similar to what jeffc said). If this SWAG (scientific wild arse guess) is correct, I would expect that conditions would need to be just right for this to occur, and be short lived and pretty rare, therefore I wouldn't expect to see mold.

 

[mtlogcabin]

How old is the home?
Newer homes require whole house ventilation fans or Heat Recovery Ventilators which may not have been installed correctly and are pumping warm moist air into the attic.

 

[Mr. Inspector]

You never said if the attic is vented or how it's vented.

 

[twoply]

We had a big rain and most of the snow melted. It snowed again. I went back to the house. It is nice and evenly coated today.

No vents terminating in the attic. No sources of heat noted. 7 inches of blown in insulation over 3 inches of old batt insulation.

 

[twoply]

Sorry, Ridge vent and soffit vents.

You never said if the attic is vented or how it's vented.