Frost pattern on roof

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  #1  
Old 01-17-18, 09:27 AM
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Frost pattern on roof

What do you make of this frost pattern? I had blown in cellulose installed two years ago with baffles and air sealing. Why would I still be getting this air leakage? Should I be concerned about this? And then on the front of the house I can see frost melting where the stairs are located. Does this mean they didn't air seal properly?
 
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Old 01-17-18, 10:12 AM
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Heat is radiant energy. Insulation does not stop heat loss, it only slows it. Your roof melts first where your top plate is closest to the roof... heat is also conducted by the rafters which are probably buried in insulation. You will also have air leakage at horizontal plywood seams (4' on center as you go up the roof) which lets warm air in the attic seep out. But it's most noticeable the closer the roof is to the ceiling.

This does not indicate anything was done improperly. It's simply an indication of heat loss which is impossible to prevent.
 
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Old 01-17-18, 10:16 AM
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If its the pile of snow I would be more concerned if there was a bare spot meaning a leak or lack of insulation.

Doubtful you have a massive pile of insulation that keeps that one spot covered with snow.

Was it a drift? How does the roof compare to neighbors?
 
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Old 01-17-18, 11:33 AM
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Thanks for the replies. Just worried about ice dams which were bad before the insulation job. The pile of snow was a drift. We then had the classic January thaw melting most of the snow. So no amount of air sealing is going to prevent this air leakage?
 
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Old 01-17-18, 11:40 AM
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Nope. Heat rises. If you had continuous soffit ventilation letting cold air in at the soffit, and continuous ridge ventilation letting that air out at the top (ventilates and also keeps the roof decking closer to exterior temps) it might succeed in carrying this heat away faster... but the close proximity of the heat source is enough to melt the frost.

If they blew that area FULL of insulation and there is NO ventilation, you might be seeing the area just above that insulation melt first, since that would be where the heat is escaping out of the insulation into the attic space.
 
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Old 01-17-18, 11:51 AM
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Full soffit and ridge venting with baffles. Any idea why I'd be losing heat above the stairs?
 
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Old 01-17-18, 11:54 AM
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Heat rises. The stairway acts like a chimney..........................................
 
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Old 01-17-18, 12:22 PM
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Right but there must be an air leak somewhere to let all that heat into the attic. Maybe I'm over analyzing here. Just don't want an ice dam and leaks as I have in the past. Haven't noticed any so far but sure would like to plug any remaining air leaks.
 
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Old 01-17-18, 12:47 PM
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You said that you had a drift there, by which I assume you mean there was more snow there than elsewhere. Nothing wrong with that. The wind whips around different roofs differently, and the manner in which it is deposited has little to do with the amount of insulation you have. So it only makes sense that if there was more snow there to start with it's going to take longer to melt. And no matter how much insulation you have, yes, you have heat loss. If not for heat loss we could all just close the doors for the winter and save the money we spend on gas bills. So as heat transferred through the roof and melted other areas it was slowed down by the additional snow in this area, melted underneath, froze to ice overnight, and repeated itself for however many days. So you ended up with ice in that area, and it's simply taking a little longer to melt than it did the rest of it. Like Marq said, I would be more concerned if you had an area without any cover than I would with what you have. I don't think that you have anything to worry about there. Just my 2 cents worth.
 
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Old 01-17-18, 12:58 PM
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The area over the stairs is probably (just guessing) a slopped ceiling?
Does your upstairs have a partial slope to all the ceiling along that row a few feet back we are seeing?
Sounds like your air sealing and insulation was a step in the right direction but you ask " So no amount of air sealing is going to prevent this air leakage?" and that is not correct. I see new construction going up all around me that are covered with a nice blanket of snow and never an icicle to be seen.

With a retrofit it becomes a trade off of how much effort can they put in for those last small leaks. When new they can get almost all leaks.

Ice dam conditions vary a lot and your only way to judge will be to watch other houses and compare them to yours. Hopefully you will see far less than before.

Bud
 
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Old 01-17-18, 01:12 PM
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This is all great info. Yes, gambrel style roof and sloped ceiling going up the stairs then in the back of the house too. What did they do back in the 70's? Just live with ice dams or we're houses so inefficient that the heat never made it to the attic? Serious question since the house was built in 1970. And yes, much fewer icicles now.
 
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Old 01-17-18, 01:15 PM
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I think it is just a remnant of a drift on the roof and has no relationship to an "ice dam".

I see these frequently through the winter and the locations change depending on the wind direction during and just after a snow. The snow removal on a roof is from the radiant heat of the sun and some spots get random drifts. I see them frequently on the east facing slope of the roof (cool morning sun) and rarely on the west slope because the sun is warmer and our prevailing wind after snow is from the west. They are common after an "Alberta Clipper" snow that drops 3" to 6" of "sissy snow" (relatively light snow) followed by cold clear days and lows of 5F or less.

You only worry about ice dams when you have ice down to the edge of the roof surface.

Dick
 
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Old 01-17-18, 01:59 PM
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Yeah, not worried about that snow spot. The rest of the snow melted when we hit 50 degrees for two days. That one spot was just deeper. More curious about the frost pattern and heat loss.
 
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Old 01-17-18, 03:47 PM
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Dick, if you paste that picture into a word doc and lighten it up you will see the rafters and what looks like a knee wall about 3' up.

Zaffa, years ago they didn't install as much insulation and just melted all of the snow off so no ice dams. As we became more concerned about energy use and cost we increased the insulation and other aspects and now have to deal with the side effects. I remember paying $0.16 a gallon for gas and assume my dad paid less for fuel oil, those days are gone.

As for the sloped ceilings they are probably 2x6 so 5.5" minus 1" for air and you have at best r-15 and modern guidance would want r-40 or higher. Getting r-40 into those rafters with a 2" air space above isn't going to happen and if it did would still take a long time to pay back the cost.

Bud
 
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Old 01-18-18, 09:03 AM
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Another thing I saw this morning: random water droplets on my siding in back of the house. It snowed last night and there is no ice damming. I also have ice/water shield. The water is clear and not coming from the soffit. There is some coming out of the bathroom windows from condensation. Seems to only happen when it snows. Haven't noticed it in the rain. Is the gutter causing melt water to back up under the fascia and then down the back of the siding.? Or is it really just random condensation? I installed the gutter myself. It is plastic attached via plastic clips screwed into the fascia under the drip edge. I'm realizing now I did not seal those screw holes (dammit); could water possibly get in via those screw holes?
 
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Old 01-18-18, 09:20 AM
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This is an ice dam. If you have this you have a serious insulation issue where heat is escaping, melting snow which refreezes at the overhang/gutter.


https://www.doityourself.com/forum/a...1&d=1516292391
 
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Old 01-18-18, 09:33 AM
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The first sign of an ice dam are the icicles. Next is often water or more icicles coming from the soffit behind the fascia board. Next is ice running down the face of your siding and possible water coming through the ceiling inside. A few drops of moisture on the siding after a snow is of not a concern.

Bud
 
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Old 01-18-18, 09:35 AM
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I don't even have icicles never mind ice build up. Must be condensation bleeding through the siding.
 
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Old 01-18-18, 01:39 PM
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Just to be clear, you said " Must be condensation bleeding through the siding." not sure what you have for siding but I know of none where moisture might bleed through and form water drops on the outside. The outside can get very cold at night and collect condensation from early morning warmer air. My vinyl now does that due to extra insulation behind it.

Bud
 
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Old 01-18-18, 04:29 PM
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I have vinyl siding with one inch foam insulation behind it. Siding is not water tight. It has weep holes to let water out. That's probably what I'm seeing.
 
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Old 01-18-18, 04:53 PM
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Vinyl siding does fit together very loosely and easy for snow to be blown in behind. And when it melts it could well drip down the front as you stated. Bleeding would be like moisture coming through the siding.

Thanks
Bud
 
 

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