Ice dams


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Old 09-20-21, 10:32 AM
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Ice dams

Last winter, for the first time in 18 years, after a fall 2020 roof replacement, I had ice dams and leaks, water only coming through the soffits, however (and fortunately).

The house is a ranch, and the attic floor is isolated with plywood on top. However, brick chimney needs to be isolated, which will be done.

Now, two problems:

- V-shaped ceiling in one room, with ceiling of one V leg just a few inches away from , and parallel with, the roof. No insulation. I would think that foam insulation would be best. Any issue with humidity (do I need some kind of screen or Ö)?

- Soffits are solid plywood. I want to replace them with plastic panels with holes/slits to let cold air into the attic.


I also need to look and see if attic floor insulation has been put too far onto the soffits so that it blocks air from coming into the attic. Can see this only from the outside, so I need to remove the plywood soffits.

A problem with cold air coming into the attic is, of course, that the existing ridge vents are often blocked by snow.

I would greatly appreciate any comments on the above (soffit replacement and roof insulation in particular).

Hans L
 
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Old 09-20-21, 09:20 PM
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Attic insulation goes in the ceiling (attic floor) not in the rafters. Your climate zone will tell us how much is recommended.
"Last winter, for the first time in 18 years, after a fall 2020 roof replacement, I had ice dams and leaks, water only coming through the soffits"
Sounds like the new roof changed something. Check to be sure they opened the ridge area properly. A common mistake where they initially cover the top when installing shingles but forget to go back and cut out unwanted underlayment or shingles.
If plywood soffits where was the low venting before?

Bud
 
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Old 09-21-21, 07:18 AM
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Hello Bud, and thanks for replying.

My attic insulation is in the attic floor. Now, it is very hard to see, in the wedge of the roof and attic floor (head won't fit :-) if the insulation extends out too much, so I would like to look at it (and remove, as needed) from the outside, which requires removal of the plywood soffits. And plastic panes with holes would give much more ventilation than the few vents that are in the plywood soffits today.

The previous roof was, as I remember, a double layer of tar tiles. That may have made the difference.

I will check the ridge vents, but if they are snowed over, it might not make a great difference if they work okay or not.

Kindly let me know what you think.

Hans L
 
  #4  
Old 09-21-21, 09:00 AM
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Here in Maine I occasionally see snow conditions that block the ridge vents, but rare. Usually open one side or soon after the snow. The warm air at the peak finds a way through.

Still not obvious what changed with the new roof to now have ice dams where you apparently did not before. What was in place for high venting, did it have a ridge vent or other?

Bud
 
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Old 09-21-21, 09:55 AM
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"Here in Maine I occasionally see snow conditions that block the ridge vents, but rare. Usually open one side or soon after the snow. The warm air at the peak finds a way through."

Here in Cleveland, Ohio, we had quite a lot of snow and cold temps for a while last winter. I will look this winter for openings at the ridge vents.

"Still not obvious what changed with the new roof to now have ice dams where you apparently did not before. What was in place for high venting, did it have a ridge vent or other?"

With two layers of asphalt shingles before, I guess that the water did not get through. Now, with one layer, and in spite of 6' of "roof and water" (plastic sheets), water got through (nails through shingles and plastic, and the plastic did not close around the nails; bad quality?).

I had ridge vents on the previous roof.

So, there I am :-)

Hans L
 
  #6  
Old 09-21-21, 10:00 AM
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Ice dams are due to heat escaping through a weak spot in the insulation, melting the snow on the roof during the day then freezing overnight. I think you've already answered part of your question with the concern over insulation in the soffits. That's a critical area of the insulation envelope where the thickness of the roof narrows down to the rafter depth at the perimeter.

Probably best to remove an insulation in the soffits, and you can probably get at it with a shop vac and long extensions. Then add a styrofoam baffles to maintain a vent space between the rafters and under the sheathing. Then you can add more fiberglass insulation along the edge, probably R19 unfaced batts, between the floor of the attic and the foam baffles.
 
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Old 09-21-21, 10:11 AM
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I suspect the primary ice dam problem is due to insufficient insulation under that plywood floor. The plywood also creates a condensation plane where warm moist air from the house can reach the cold plywood. Correcting that isn't easy.
As for new shingles with Ice and water (I assume) under them they should not be leaking. But they should also not be getting flooded by snow melt.

Is this a ranch where you can clear the snow after big storms?
Air leaks from house to attic are often many. However it is the larger leaks that cause the most concern, vent pipes, chimneys, attic hatch, are a few. One of my primary tools for energy inspections is my infrared camera. I find it works best in cold weather, easier to see the hot spots. You can rent them.

Bud
 
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Old 09-21-21, 01:22 PM
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Bud & Yadkin:

I mentioned one thing that you have not commented on. I have a V-shaped ceiling in one room, and one leg of the V is very close to the roof, with no insulation in between. That is one huge leak! Can I fill the space between the ceiling and roof with insulation foam (I would have to hire someone, most likely). Anything else that would have to be done there (sheets of something as humidity screens)?

Otherwise, I feel rather confident about what to do: isolate the chimney in the attic, remove any insulation at the soffits, close the insulation space between ceiling and attic floor plywood at the soffits to prevent warm air to reach the soffits, and replace the plywood soffits with holed/slit plastic (as used as soffits when house walls are "sided" (siding added).

As for raking, yes, this ranch can probably be raked. And I will rent an infrared camera to check during the winter.

Yadkin, I am not entirely sure I can follow the "geometry" of this:

"Then add a styrofoam baffles to maintain a vent space between the rafters and under the sheathing. Then you can add more fiberglass insulation along the edge, probably R19 unfaced batts, between the floor of the attic and the foam baffles."

If you care, kindly elucidate me.

Best regards, and thanks,

Hans L
 
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Old 09-28-21, 04:10 PM
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Here's an illustration. The styrofoam baffle is thin, blue, on top of the thick, pink fiberglass insulation. Note the air flow going between it and the underside of the roof sheathing.

Ideally you want 12" of fiberglass, but the angle of the roof (in this case) requires it to taper.

 
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Old 09-28-21, 04:16 PM
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A better design allows the full thickness of insulation to continue to the top of the wall, However this adds cost that few will appreciate. Thus the newest building Code allows the insulation to taper.

 
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Old 09-28-21, 07:07 PM
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Yadkin. thanks.

My situation is not the same, however, and I have discovered that there is, actually, insulation (of
a 1963 fashion) between the roof and the ceiling.

I will remove the plywood soffits and report back.

Hans L
 
  #12  
Old 09-28-21, 11:06 PM
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One point, insulation into the soffit is not necessarily a bad thing, I have seen many homes where that area is filled with insulation.

As the illustrations point out the weak point is the area directly above the exterior wall where the insulation is the thinnest, that is where (other than air leaks) you get heat loss into the attic/on the roof deck melting snow etc.

The baffles allow air flow through the soffits which is a different situation, attic ventilation. But installing the baffles for low pitch roofs displace insulation. As long as the proper ventilation is there the excess is not causing any issues.

Soffits are solid plywood. I want to replace them with plastic panels with holes/slits to let cold air into the attic.
​​​​​​​https://www.owenscorning.com/en-us/r...ent-calculator

There are many options, but you need to do the calculations to get the required sq inches of soffit and ridge vents
 
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Old 09-29-21, 04:36 PM
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Okay, Marq1. I'll go ahead and remove the plywood, and go from there (one road: reread all the posts and figure out from them what to do).

Hans L
 
 

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