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Old 11-23-2007, 12:12 PM   #1
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Ice issue - even after improving ventilation


Hi,

Winter came in full force for us yesterday. I'm struggling to resolve ice issues on my roof. I've got a new roof in Sept. with an ice shield, new Maximum Ventilators (which are now being used everywhere in Ontario and Quebec), and yet I'm still getting ice build up on my lower roof. I know it's a ventilation/insulation problem, but I can't figure out what's the best way to solve the problem. The low roof is uninsulated with soffit ventilation and a small vent at the end. I am wondering if a roof-to-wall vent is necessary?
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Old 11-23-2007, 01:07 PM   #2
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Ice issue - even after improving ventilation


That is winter in full force? In some areas, that would be described as a cold October. Winter takes time AND temperature swings from moderate to cold.

If you have some snow, you will get some ice buildup on the roof edge even with metal slip surfaces, heat or religiously remove the snow. It is a natural process and the key is to not get an excessive amount. Depending on the exposure to sun, the buildup will vary with the swings.

Before you decide you have a problem, let your new roof perform as it was designed to.

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Old 11-23-2007, 02:55 PM   #3
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Ice issue - even after improving ventilation


It appears to be working fine. I can't see any icycles in the porch roof area. They all appear to be on the face of the gutter.
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Old 11-23-2007, 03:03 PM   #4
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Ice issue - even after improving ventilation


Even icicles are not really bad. - They form when the moisture freezes before it has a chance to hit the ground. All moisture(rain, snow, dew, frost) on a roof eventually has to come down.

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Old 11-23-2007, 03:13 PM   #5
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Ice issue - even after improving ventilation


Ventilating the porch roof where it abutts the wall of the main house will provide absolutely Zero benefit. The porch roof is already a "Cold" roof or underside of the roof decking configuration, by not having any underneath heat permeation from the interior house.

Also, it has no insulation you stated. Therefore, there is no reason known in any studies I have read that would alleviate the porch snow remnants.

Some people are looking for miracles, but no "Safe" product will prevent nature from taking its course. Snow happens. Electric heat tapes or cables would melt the snow and ice, but could lead to a potential fire hazard and also a melting of the shingle surface they are attached to.

It is the beginning of winter and you live in Canada.....Need I say more?

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Old 11-23-2007, 07:05 PM   #6
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Ice issue - even after improving ventilation


Hi Andy,

I wouldn't worry about the second roof lower down, as you are probably getting the water on it from above (ie, the top roof). So that's where I would look to correct the situation.
I'm a neigbour of yours, down the 417. Let's start with the basics. We need R38-R40 of insulation in our attics. Fiberglas bats are usually around R2-3 per inch. So if you have less than 12 inches of fiberglas bats in your attic, you're getting excessive heat loss.
Second, it's fine to use the Maximums (and they ARE good vents), but if you have inadequate air intake at the soffits, then the Maximums are not going to do it all by themselves. Are your soffits ventilated and unblocked? If not, then you don't have good ventilation.
Do you have gable vents? Sometimes these "short-circuit" the air-flow and have good ventilation between the gable vents and the Maximums, but this doesn't do anything for dissipating the heat loss along the eaves.
Sometimes the soffits are vented and unblocked, but the air still isn't getting into the attic because the insulation bats are pushed into the eaves and leave almost no space between the insulation and the sheathing to allow air through. You need a minimum of 2" as an air channel.
I obviously don't know your actual situation, but I am guessing that you may not have very good insulation in the attic, which is leaking lots of heat into the attic. You also probably don't have great ventilation there, so the heat buildup is conducted to the roof, where it melts the snow. This water drips off the top roof onto the seond roof and freezes there. But, I AM guessing.
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Old 11-24-2007, 06:33 AM   #7
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Ice issue - even after improving ventilation


The thing I took note of is this; The snow appears to be 'even' from eave to ridge. We don't live in snow country, but some years get as much as 23" in 1 storm.
When we get problem calls, the poor insulation has heated the attic spaces and there is No snow near the ridge, but big buildups of ice dams at the eaves.

Is my observation valid, or do I need to learn more? I'm open to all input.
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Old 11-24-2007, 09:52 AM   #8
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Ice issue - even after improving ventilation


Frank, your observation is valid. When the attic is not "cold" then the pattern you see is... first an even blanket of snow over the roof, then as the snow melts on the warm parts of the roof it settles down, while along the eaves you will see more and more icicles and the appearance of ice along the lower edge of the snow blanket. After a week or so, the upper area of the roof will have melted all the snow off so you can see the shingles, while a large ice dam would have developed along the eaves.

If there are gutters along the eave, they trap the water that would have dripped off the eave on the icicles. That water then freezes, and the gutter quicly fills up to the edge with ice. At this point, depending on how well the eave is constructed, the water starts forcing itself into all the nooks and crannies along the eave and you start seeing the first leaks.

The amount of snow cover on the roof, and the degree of cold also play an important role in ice dam formation. Snow is a good insulator, and if the blanket of snow is fairly thick (say, more than 6 inches), you can have a significant difference between the temperature at the top of the snow, compared to its base. However, once the base of the snow reaches the melting point, it melts (duh!). The other factor is what the outside temperature is. If the outside air is -20F, it will take more heat from below to raise the temperature at the base of the snow blanket to melting, than if the temperature is just below freezing. That's why you see much more ice damming when the temperature is relatively mild, compared to when it's really cold.


The top half of the photo shows a roof which gets persistent ice dams immediately after a snowfall. Note that the snow blanket is even across and there are minimal icicles along the eave.

The lower half shows the same roof after two weeks. The blanket of snow is now uneven due to the melting, and the ice dam and icicles are clearly visible along the eave.


This shows the same house at another time, when the snow had time to melt off the hottest parts of the roof. It is interesting that the hottest part of the roof is over an apparent empty space alongside the room on the second floor, and is vented by a small gable vent. That empty space is probably not insulated, and certainly has no air flow to vent the heat out. The result is that the house heat melts the snow that accumulates on the roof.

Now, I may not have made reference to the pictures correctly, so they may or may not appear. If they don't I will try again...

Last edited by pgriz; 11-24-2007 at 10:24 AM.
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Old 11-24-2007, 06:10 PM   #9
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Ice issue - even after improving ventilation


Gotta agree with Ed on this one.
Theres icicles on the porch eaves,which aren't from heat loss.maybe your over thinking it.

Last edited by oldfrt; 11-24-2007 at 08:25 PM.
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Old 11-25-2007, 08:47 AM   #10
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Ice issue - even after improving ventilation


THanks for the album pgriz. NIce pics. Looks cold up there! I'm shivering now. I was warm until I looked.
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Old 12-01-2007, 11:25 PM   #11
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Ice issue - even after improving ventilation


Well said PAUL,andEd,you usually don`t vent unheated air spaces,and to do it at that wall would hurt the insulation factor of that wall as well
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Old 12-01-2007, 11:26 PM   #12
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Ice issue - even after improving ventilation


remember the key is use of all 3 ,insulation,ventilation,and waterproofing---one by itself will never solve the problem !!
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Old 12-02-2007, 04:07 PM   #13
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Ice issue - even after improving ventilation


Most likely it's build from the roof above as pgriz said. The other potential heat loss area though is from the bond area behind the porch roof. Many times they're not insulated sufficiently.
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Old 12-12-2007, 11:50 PM   #14
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Ice issue - even after improving ventilation


it could also be heat loss,thru the bearing wall from under the porch,because those walls never have enough insulation,it requires heat loss from a heated structure for this situation to occur regardless

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