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Old 07-05-2011, 06:04 PM   #1
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Ice Dam Prevention Suggestions


I've read several posts here about preventing ice dams and what to do with ventilation and insulation. I do not know much about construction, so I have been doing all I can to research the science behind preventing ice dams. I have found a lot of good info on this forum, so I thought I would post my case and see if anyone has any advice to offer.

I have an old 1.5 story home. When the home was first designed in 1942, the upstairs was solely meant for an attic. A homeowner built a bedroom into the attic, and I have been experiencing the ice dam problems that come with it (due to Minnesota climate). Water came in through the attic crawlspace and into my kitchen. Icicles formed inside my attic crawl space. I would like to prevent that from happening in the future.

Here is a picture of the south side of the roof:

http://postimage.org/image/sns4fv7o/

A large ice dam forms where the 2 slopes of the roof meet.

There is a bit of a crawlspace between the drywall and the frame of the house. Here are some pics of that:

http://postimage.org/image/sop76t38/

http://postimage.org/image/spap6bic/


The roof has no soffits, and I am not sure if they can be added. Here is the only place where I see that inside air can be drawn in. It is on the end of the roof farthest from where the ice dam forms:


http://postimage.org/image/15qrg5vo/


And here is how I think the hot air can rise past the drywall to the vents on the top of the roof (There is more than one of these in the crawlspace):

http://postimage.org/image/162c7lc4/



I had an insulation guy look at it and he thought that he would remove all of the cellulose insulation on the floor of the attic, and add the following insulation:

  • Install 3, R-21 sprayed closed cell urethane to rim and gable end walls
  • Install 3 , R-24 sprayed urethane to slope ceilings behind knee walls
  • Cover foam with 1, R-7 fire rated thermax, Total R-31 slopes and gable end walls

I am curious if the above treatment will help and if anyone has any other suggestions.

When I eventually have to re-roof, I plan on doing something like Dan Perkins suggests in the November 2008 issue of JLC.

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Old 07-05-2011, 07:56 PM   #2
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Ice Dam Prevention Suggestions


Dig away that blown in insulation and see if you can get to the soffits. Maybe take a picture of what you see. I think that is all you should need to do.

I don't think the insulation guys advice will help, and it will void your shingles warranty (assuming it still has any)

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Old 07-05-2011, 09:11 PM   #3
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Ice Dam Prevention Suggestions


The problem is I don't have any soffits, and I don't think there is room to install them if I wanted to.
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Old 07-06-2011, 02:43 PM   #4
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Ice Dam Prevention Suggestions


If there is no soffit to ventilate, why couldn't roof vents be installed low on the roof (near the eve) and thereby serve the function of a ventilated soffit? It might look a bit odd but shouldn't it work?
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Old 07-07-2011, 11:43 PM   #5
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Ice Dam Prevention Suggestions


Soffit vents on the ridge might be a possibility. Since I do not know much about roofing, do you think it would help?
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Old 07-08-2011, 12:34 AM   #6
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Ice Dam Prevention Suggestions


From the exterior picture, it looks like you already have a few hat vents near the ridge - adding more at the ridge won't help. To get the proper air flow you definitely need an 'intake' at the low edge of the roof. It looks like there is a 4"-6" overhang - where the electrical service conduit penetrates through. If you install some vented soffit along that overhang, is there anything on the inside that would prevent airflow under the roof deck?

Moving the insulation to the underside of the roof deck is a step in the right direction. That keeps the heat below the insulation - in the crawl space behind the bedroom wall - and prevents the cycle of thaw and refreeze that happens now when the heat above the ceiling insulation warms the underside of the roof.

You'll also need to extend the pans between the rafters down to the soffit, if you can get it ventilated, to continue the thin space for air movement between the roof deck and insulation.

If venting the narrow soffit is problematic, you might look into fascia vents - thin vertical venting strips that install behind the fascia board.
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Old 07-08-2011, 10:21 PM   #7
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Ice Dam Prevention Suggestions


If you don't think you have room to install soffit vents, I would try an 'Edge Vent' type product. It goes on top of the sheathing (under the shingles) Google it.
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Old 07-10-2011, 05:50 PM   #8
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Ice Dam Prevention Suggestions


Quote:
Originally Posted by shazapple View Post
If you don't think you have room to install soffit vents, I would try an 'Edge Vent' type product. It goes on top of the sheathing (under the shingles) Google it.
These edge vents may invite water infiltration when ice damming forms though.

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