weatherization and ice dams


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Old 01-22-23, 01:38 PM
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weatherization and ice dams

I had my house weatherized last fall. Pertinent items that were done include removing rafter insulation and insulating the upstairs knee walls instead, combined with 20 inches of blown cellulose behind the knee walls and along the flat midline of the attic space. 2 new vents were also installed. My energy use seems significantly less, but my ice dams are the worst I have ever seen them. Much, much worse. They have gone from bad to severe.

Coincidence? Warmish weather this winter may have contributed, to an indeterminate degree, but I thought my ice dams would be greatly reduced not increased after weatherization. I've got icicles coming out of the soffit vents in a few places, which is a bad omen.
 
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Old 01-23-23, 12:26 AM
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20 inches of blown cellulose
20" of cellulose is around R60, you should not have any significant amount of heat loss through all that, cellulose is also very effective at air sealing, should be a much better situation over what you had.

removing rafter insulation and insulating the upstairs knee walls instead,
It's difficult to know exactly what your insulation system was before but ice dams are as much about sufficient insulation as they they are about where that insulated exists.

The areas at the corners of the rooms, right at the top plate is a trouble spot. If the prior insulation was sufficiently packed/folded into these areas but was removed and new insulation was piled onto the ceiling but didn't get replaced in this area then greater heat loss will result creating worse ice dams.


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Old 01-23-23, 10:54 AM
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Yes, likely weather related. If you have snow sitting on the roof and warm weather that's melting snow from above, you're going to have ice dams on a cold roof. Or ice dams from heat loss that freeze once the water runs to the lower colder parts of the roof. No ice and water shield will mean roof leaks. But hopefully your felt will largely protect the sheathing.

People who have ice dams problems with no other solution need to rake snow off their roofs to limit the amount of snow melt.
 
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Old 01-22-23, 02:32 PM
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If you have increased the insulation in the attic..... then you will need to confirm or increase air flow thru the attic. The roof deck needs to be cold or you'll get a lot of melting snow and ice dams.
Also a problem on shallow pitched roofs.
 
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Old 01-22-23, 02:34 PM
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If your attic space is warmer the roof deck will be too. That can lead to more melting on the roof. But if you have a lot of snow and a lot of melting that could be the real reason.

You need to have plenty of ventilation between the insulation and the roof, and fresh air to keep the roof deck cold. Ice coming out the soffit vents likely means you don't have adequate ice and water shield under your shingles. If the ice is coming from the attic the likely culprit would be poor air sealing prior to adding insulation.
 
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Old 01-22-23, 09:21 PM
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Sounds like a cape with those side attics. Outside pictures would help.

Icicles dripping from soffit areas means you have water under your shingles.

As mentioned, air sealing should have been a top priority before the new insulation. However, often air leakage from larger leaks is the big contributor. If you have a basement where you can access plumbing penetrations air sealing all you can will help. Attic access points can also be a big source of air.

Do you have recessed lights in that ceiling?Does your bath fan exhaust to the outside?Do you have a low slope area such as a bathroom up there or other low slopes.

What do you have in place for ventilation? Soffits, gables, ridge vents, roof vents, other?

Bud
 
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Old 01-22-23, 11:01 PM
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If you have increased the insulation in the attic..... then you will need to confirm or increase air flow thru the attic. The roof deck needs to be cold or you'll get a lot of melting snow and ice dams.
Also a problem on shallow pitched roofs.
Its a very steep roof, hence the knee walls on the 2nd floor. There were 3 turtle vents in the roof and 1 end vet before, and they added 2 new vents on the end that didn't have any before-1 on each side for each knee wall. So there should be plenty of ventilation.

Ice coming out the soffit vents likely means you don't have adequate ice and water shield under your shingles. If the ice is coming from the attic the likely culprit would be poor air sealing prior to adding insulation.
The roof is ancient, and I have no idea if there is ANY water shield. (and there's no money for a new roof) I'm sure the water is meltwater though, its not coming from the attic.

Sounds like a cape with those side attics. Outside pictures would help.

Icicles dripping from soffit areas means you have water under your shingles.
Its not a Cape, its more like a long weird one-off 1.5 story A-frame. Yes, I get the water is under the shingles. That's why I'm concerned. It's not the first time I've had issues but I've never had ice dams this thick.

I know they did air sealing. There were no entries into one of the knee walls or the attic, but they put in insulated access doors. I can't imagine why any of the spaces would be warmer than they were before.

Do you have recessed lights in that ceiling?Does your bath fan exhaust to the outside?Do you have a low slope area such as a bathroom up there or other low slopes.

What do you have in place for ventilation? Soffits, gables, ridge vents, roof vents, other?
No recessed lights. Bathroom fan vents outside. Upstairs bathroom has a dormer but that's the only part of the roof that isn't STEEP. I have soffit vents the length of the house and 6 vents as previously described. The area around the dormer is the one spot they did NOT weatherize as described because there are pipes in there. That part I expect to have ice dams because it is warmer, but the dams are worse than I've ever seen them on the rest of the roof too. They are humongous.
 
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Old 01-23-23, 09:55 AM
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It's difficult to know exactly what your insulation system was before but ice dams are as much about sufficient insulation as they they are about where that insulated exists.
The idea was to make most of that knee wall space colder by removing the rafter insulation (which was R22, IIRC) and insulating the floor in there and the knee walls with cellulose.

I don't know what they did in the corners and with 20" of cellulose in there I'm not inclined to try and find out. I suppose I could rent an infrared camera and see if it gives any clues

Funny thing is, before the weatherization there used to be visible snow melt on the roof, so much so that you could see where the rafters are. I don't see that anymore, but there are still a couple areas wher!e roof shows. One is at the peak. Another is where the roof connects the house and garage. But still its far, far less than before, and is mostly noticeable in these small areas only because of where there IS thick amounts of snow and the insulation is doing its job.

There is still a chance this is mostly weather related because we have had 50 inches of snow but a relatively warm winter.
 

Last edited by worker9999; 01-23-23 at 10:50 AM.
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Old 01-23-23, 09:20 PM
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People who have ice dams problems with no other solution need to rake snow off their roofs to limit the amount of snow melt.
I just heard we've been 11 degrees above average this month, so that has surely contributed.

I tried raking but even with an extension I can't even get near halfway up the roof and there is so much snow in the yard this year its impossible to access much of the perimeter anyway.

I usually go elsewhere in winter and leave the house unheated, so no ice dams. Must remember to do that again next year...

This is about what my ice dams look like right now (that's not my house). Very nasty.


 
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Old 01-24-23, 12:17 AM
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Need to see your house to judge the ice vs the construction. The house pictured has a severe heat loss issue into the attic. You said the roof is ancient how old is the house.

My current thinking is you have a ventilation issue related to the insulation work they did, but need a picture or two.

Bud
 
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Old 01-24-23, 07:21 PM
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Just saw a news article that its the worst ice dam year for at least 10 years, and 12 years ago was the worst in 20 years. So that sets my mind at ease. I'm gonna see if I can melt some channels in it

I
 
 

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