Ice dams and no soffit vents

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Old 12-10-10, 05:37 AM
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Ice dams and no soffit vents

We just moved into a house and without any significant snowfall I can already see small ice dams starting.

The house has a fully accessible attic (with r30 and plywood floor), full length ridge vent but no soffit vents.

I plan on adding soffit vents in the spring. In the meantime, there are two small windows at either end of the attic. Would it help to open these a little bit to allow cold air in, allowing the warm air to escape from the ridge vent?
 
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Old 12-10-10, 06:18 AM
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It might help. But most ice dams are due to shallow rafters. The heat coming off the ceiling and exterior top plate hits the roof- and when only a few inches separate the two, it's pretty likely that an ice dam will be the result.
 
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Old 12-10-10, 08:24 AM
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hope it doesnt come to this but 1st month in my house i found water pouring in the bedroom ceiling. i never went out back in winter and didnt know about dams and things to watch out for. huge block of ice in the gutters so i got out my hose, hooked it up to the washer HOT and voila ,the ice was gone. i got to meet the neighbor that way too

got roofing tape right after that but strangely havent had that same problem in over 15 years even though i rarely put the tape on anymore and we got 80 inches of snow last year. I have full attic like you described and the windows are open a bit all the time because of certain issues so i get plenty of cold air in there and circulation. I can only imagine it's all that cold air coming in that's saved me all these years. I just insulated my attic this fall but dont have access above the bedroom unfortunately
 
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Old 12-11-10, 06:21 AM
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Originally Posted by XSleeper View Post
It might help. But most ice dams are due to shallow rafters. The heat coming off the ceiling and exterior top plate hits the roof- and when only a few inches separate the two, it's pretty likely that an ice dam will be the result.
When you say shallow, do you mean roof pitch? Mine's actually 7/12, with x6 rafters.

Lucky,

In my reading on this I think my biggest heat loss in the attic is the stairs leading up to it. I see corning makes a stair insulation kit. Gonna check that out this weekend.
 
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Old 12-11-10, 07:43 AM
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I guess I meant that several things are involved, more than just ventilation. Heat loss, ventilation, roof pitch and rafter size are all interconnected in causing ice dams.

What I see a lot of the time are 2x4 rafters... either no/very little soffit venting, and a lack of insulation in the attic. The proximity of the roof to the ceiling causes a lot of melting right above the coldest part of the roof (the soffit) Where is the bulk of your ice dam occurring?

I have always wondered if installing nailers and rips of foil faced Thermax between every rafter (like styrofoam proper vents) would help block the heat loss in these areas and help keep the surface of the roof below freezing.

I just worked at an old 3 story farmhouse where a different contractor had removed ALL their old soffit and installed vented aluminum soffit. As a result, they have TOTAL ventilation up in their attic now, and when the wind blows, air goes in one side of the house and out the other! So it's about as cold in their attic (3rd story, full floor) as it is outside. They now have the same problem with a cold stairway, and they say the upstairs feels colder as well- all that air moving is probably speeding the heat loss from the house. They are about fit to be tied.
 
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Old 12-13-10, 06:58 PM
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Sorry for the delayed reply.

My ice dams are at the very outside edge of the eve. Snowmelt seems pretty even without any real hot spots.

The whole attic floor is full of r30 pink stuff with 23/32 plywood flooring over it. The only un-insulated spot is the stairwell leading up. I know I must have a lot of heat loss here. Over the weekend I fashioned a "cover" for it with 1" foam board insulation. The stairwell is staying a lot warmer now.

But I know my root problem is absolutely no soffit vents. There's the ridge, but nowhere for fresh air to get in at. I'm going to get after that as my first spring time project.
 
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Old 12-13-10, 07:38 PM
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I have a 1950s cape. Attic was not really finished when I bought the house. I had since put a small dormer, about 12 ft, for 2nd bath up there. I thought about adding soffit vents but my roofer told me not to because of the heat loss involved. I have since moved the oldest son up there and am soon to move the 4 yr old soon. The roof joists are 2 x 6 and was well insulated when I had the roof replaced. I needed all new plywood for roof so I took advantage to improve the insulation when they had it all ripped off. The floor was old pine and no insulation under but I did carpet. I did not insulate the knee walls because the roof was already insulated all the way to the soffets. ( I should have) I have a HW basebord zone up there. I keep the t stat at 65 up there and the t stat at 70 down stairs. The heat from from downstairs keeps it at 67-68 up there.

Whats my story? I guess just for you to have something to compare with. Capes are inherently cold up stairs I think because the roof is basically the ceiling. I get ice dams but no where as as bad as I did when it was unoccupied. If you indeed have a cape which I think you do and are going to finish it off I would think twice about adding soffit vents. I do have the gable vents and the roofer did suggest the ridge vent I had put in. He also absolutly was against any type of roof fan. I asked him because in the summer it gets hot up there. He said you will just suck the heat or ac from living areas.

And as the poster said below : "They now have the same problem with a cold stairway, and they say the upstairs feels colder as well- all that air moving is probably speeding the heat loss from the house. They are about fit to be tied."


My poor kids... I tell them to put on a sweater....

Mike NJ
 
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Old 12-14-10, 06:00 AM
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Originally Posted by XSleeper View Post
What I see a lot of the time are 2x4 rafters... .
is that really common? i'd have to go up and measure but i swear i have x8 or x10. how could x4 hold anything up lol
 
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Old 12-14-10, 06:22 AM
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Only in older houses in your not-so-wealthy areas. Your house sounds like it was built well.
 
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Old 12-14-10, 06:08 PM
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thanks it was, somewhat ....they left a few hundred sq ft of 2x10 attic floor with only 2 inches of loose fill for insulation, they wanted me to see those meaty joists i'm sure is the reason. now if they only had a basement instead of a water logged crawlspace i'd be thrilled!

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maybe cracking your windows will help keep things nice and cool but putting on sweaters sure does stink
 
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