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Old 02-10-2009, 07:47 PM   #1
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Ice dam and soffet ventilation


We just moved into a 20 yo house and have had water in the basement, ice dams, and water leaking above outside doors.

I'm focussed on the ice dam problem right now and hoping it's related to the basement water and other water leaks.

Huge ice dams (as thick as 8 inches) formed on the eaves. These grew only after snowfall even though the air temperature was well below freezing all day (all month actually.) Looking at the roof it there was a definite area that was clear of snow while the other parts of the roof were thickly covered with snow. This is a simple gable roof on a back split.

Although I'm not an expert it seems to me that this an imbalance of heat loss and ventilation. It's either too much heat loss or too little ventilation.

The attic below the area of roof that is clear of snow is closed off from the other part of the attic. Through an access point in a wall I can see that there is insulation between joists and an extra layer on top. An insulation person eyed it at about 30R. There is also a roof vent about two feet from where that section peaks.

In a recent thaw we had a water coming in under the trim at the top of an exterior door under that ice dam. We hacked channels in that ice dam and allowed the water to drain. Two days later we found water under the carpet in the basement. Enough had accumulated that we could feel it when walking with socks on.

Tonight I decided to investigate why the soffets seem to be sweating. I was also curious to see if there were vents behind the perforated soffets. They were sweating because ice had formed on the aluminum soffets. In places it was 1 inch thick despite a beautiful 9C day and the melt two days prior.

Pulling off the soffets to see if there was adaquate ventilation I saw insulation stuffed into the roof joists. I assume it's the same on all joists.

I've attached a drawing to illustrate what I saw. There is no visible path for air to ventilate. Can enough air be drawn through the insulation to provide adequate ventilation?
Attached Thumbnails
Ice dam and soffet ventilation-icedam.jpg  

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Old 02-11-2009, 07:53 AM   #2
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Ice dam and soffet ventilation


Quote:
Can enough air be drawn through the insulation to provide adequate ventilation?
No. You need to pull the insulation back from the soffit.

Blocked Soffit Vents and Attic Ventilation

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Old 02-11-2009, 03:23 PM   #3
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Ice dam and soffet ventilation


Nice picture.

And Yeah, you need to pull that insulation away so that the air can circulate.

Maybe someone else can answer this question: Would some of those cardboard or styrafoam baffels provide enough ventilation in this particular case?
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Old 02-11-2009, 03:44 PM   #4
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Ice dam and soffet ventilation


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Would some of those cardboard or styrafoam baffels provide enough ventilation in this particular case?
If there is sufficient soffit and ridge ventilation.

Yes

See the above link.
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