Added New Insulation - Snow Melting in One Area


Old 02-14-14, 10:44 AM
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Added New Insulation - Snow Melting in One Area

Hi - this is my first post but I've been visiting anonymously for the past couple years.

I just threw some more cellulose up into the attic so we apparently have a R60 up there currently.

What would be causing the snow to melt only in these areas and in this sort of fashion?

Some details:
1) We have a full bathroom fan venting through one of those square vents - will be installing a proper vent when it gets warmer.

2) The soffit vent nearest to this location is not really there as the aluminum vent may suggest (just found that out).

Is a combination of these two facts the cause? Should I open up where the soffit vent shows there should be one? Thanks!
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Old 02-14-14, 11:10 AM
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Overall, it looks like a lack of ventilation of the entire roof. Make sure you have plenty of soffit ventilation (continuous if possible).

Bathrooms are notorious because they seem to be warmer on the average and definitely dump out a lot of moisture. Chimneys also cut off the circulation of the cold, drier air from the low soffit vents to the upper exhaust vents. The vertical pattern of snow melt is a sign of low air flow and little to no mixing in the the hopefully "attic" area.

All the insulation in the world has a limit what it can do if there is not enough air flow because there are always some small leaks in and around the insulation.

A better method of exhausting the heat and moisture as soon as possible should help.

Your goal is to have a roof that looks like it has a big marshmallow on it.

Old 02-14-14, 11:42 AM
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Wow - thanks Dick. I had the insulation guy back over b/c I thought he blocked the soffits or did something incorrect (I can't fit up in that attic, nor do I want to be the reason theres a hole through the ceiling) - when he checked outside there were no openings where the soffit vents were located. Just a pleasant thing to tell the owner who has only been there a few years!
Old 02-16-14, 11:54 AM
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Did the insulation guy do any air-sealing before adding insulation? Such as sealing up top plate/drywall joints, electrical penetrations, bath fan, etc... As Concretemasonry said, you want ventilation in the attic but you also don't want that warm air from the living space to be leaking into the attic either.
Old 02-16-14, 08:44 PM
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Which vent does the bathroom fan exhaust out? is it the central one in the photo or the one to the left? I'm a complete novice but if the central vent exhausts the bathroom doesn't that lead us to believe the warm air venting from the bathroom is melting the snow and not the poor ventilation in the attic which has some heat leaking into it? I only say that as why is there snow to the left and right of that vent? Are we saying that the bathroom leaks heat, makes its way to the attic and does not circulate but just melts the snow directly above the bathroom?


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