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Old 01-12-2010, 08:35 PM   #1
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Major frost in attic


Upon a curiosity look into our attic, I found very heavy frost over the entire roof and rafters. Sadly this is the first time in our 5 rear ownership that I have looked up there. Shame on me.

House is a bungalow built in 1956. 2 vents at peak of roof as well as several soffit vents.

CAUSE!!!(i think) is someone before us vented the bathroom fan directly into the attic.

Solution (i think) is to vent the bathroom fan out the roof.

PROBLEM!!! it is -28 to -38 celcius outside. Aint noone poking holes on a rooftop till at least end of April. So proper venting cant happen till then.

QUESTION ? Is it safe to just leave till spring, or should I be better to temporarily block off the bathroom fan for now.

or any other solutions till spring?

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Old 01-12-2010, 08:42 PM   #2
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Major frost in attic


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Upon a curiosity look into our attic, I found very heavy frost over the entire roof and rafters. Sadly this is the first time in our 5 rear ownership that I have looked up there. Shame on me.

House is a bungalow built in 1956. 2 vents at peak of roof as well as several soffit vents.

CAUSE!!!(i think) is someone before us vented the bathroom fan directly into the attic.

Solution (i think) is to vent the bathroom fan out the roof.

PROBLEM!!! it is -28 to -38 celcius outside. Aint noone poking holes on a rooftop till at least end of April. So proper venting cant happen till then.

QUESTION ? Is it safe to just leave till spring, or should I be better to temporarily block off the bathroom fan for now.

or any other solutions till spring?
How about not turning on the bathroom fan?

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Old 01-12-2010, 08:44 PM   #3
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Major frost in attic


shower with the door open. it humidifies the house.
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Old 01-12-2010, 09:20 PM   #4
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Major frost in attic


We rarely turn the fan on in this cold dry winter environment. Now when I say frost all over, I am talking the attic is WHITE. Looks like the inside of my freezer. 1/4" of frost.

I will try on a warmer day to see if the soffit vents are unobstructed by insulation. There is wood chips filling the floor joists with 6" white insulation on top of that.

Cant see how warm air could exist up there.....my thermometer read -22 celcius up there when I found the frost.

I am guessing this problem has always existed. But I am going to do my best to solve.

Last edited by zapblam; 01-12-2010 at 10:39 PM.
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Old 01-12-2010, 09:21 PM   #5
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Major frost in attic


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We rarely turn the fan on in this cold dry winter environment. Now when I say frost all over, I am talking the attic is WHITE. Looks like the inside of my freezer. 1/4" of frost.

I will try on a warmer day to see if the soffit vents are unobstructed by insulation.
Tape a plastic bag over the bathroom vent.
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Old 01-12-2010, 10:51 PM   #6
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Major frost in attic


Read in a few places on the web that this may just be a case of too damn cold.

Big downside is in spring when the frost melts and drips through the soffits sometimes.
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Old 01-13-2010, 12:05 AM   #7
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Major frost in attic


Since this is your first time looking in the attic, you probably don't know yet if it has been sealed properly. Do you know what the R-value of the insulation is?

There are wood chips between the rafters, under the insulation? Loose wood chips? Or is it OSB?

Do you have icicles or ice dams on your roof?
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Old 01-13-2010, 01:13 AM   #8
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Major frost in attic


OK. Its 8" of wood chips. Then 14" pink and white fiberglass batts on top of that. However while crawling around, the insulation is right to the outer walls, and I believe covering the overhang and soffit vents. I will pop off one of the soffit vents tomorrow and see. Would be a possible fix if the vents are covered up.

It warmed up to -3 today and the frost has gone away except for around the very edges of the roof. Could that also be caused by the overhang being stuffed with insulation?

I have sealed up the bathroom fan till I can get it vented correctly. There was lots of ice buildup on the roof sheeting directly above the fan and hopefully sealing for now will relieve alot of that.

No icicles or ice dams, just had a lot of snow since mid Dec. Lots has been shoveled off.

In the spring I will get a contractor to look at though.

Last edited by zapblam; 01-13-2010 at 01:17 AM.
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Old 01-13-2010, 07:25 AM   #9
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Major frost in attic


I'm not in the building business, but I've never heard of wood chips in an attic. I don't mean that in a bad way. It's just different - but interesting. Maybe it's common practice in some places.

It's a good idea to uncover the soffit vents. Ventilation could be a big part of the problem.

This is just a guess, but I wonder if the wood chips absorb moisture during the summer and fall. Then when the attic gets cold, the moisture being released from the wood chips becomes frost on the sheathing, nails, and rafters.

I would work on the ventilation issue first.
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Old 01-13-2010, 11:42 AM   #10
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Major frost in attic


Wood chips were used as insulation prior to Fibreglas batts.
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Old 01-13-2010, 01:05 PM   #11
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Major frost in attic


Wood chips, BTW, have an R value of around R1 - about the same as the same thickness of snow.
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Old 01-13-2010, 01:18 PM   #12
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Major frost in attic


Gosh, it seems like there would be big problems with bugs. Apparently not though, if it's been this way all these years.
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Old 01-13-2010, 03:24 PM   #13
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Major frost in attic


My advice would be to have a professional look at your problem. A layer of frost on all of your rafters and the underside of your decking is not a good thing, and could lead to some serious problems later.

Blocking off the exhaust fan for the time being would be a good idea, however it will not fix your problem as the majority of moisture in your living spaces finds its way into the attic space anyways.

The root of your problem is with the soffit intake vents being blocked by insulation. As long as the 2 vents on the peak of the house remain unobstructed excess heat in the attic will be able to escape through natural convection. However, without air flow through the attic, from the intake to the 2 vents on the peaks, the moisture will remain.

What has happened in your case is that the heat in your attic was allowed to escape. This is good. The moisture was left behind. This is bad. As the outside temperature got colder, the inside temperature of the attic did the same since the heat is allowed to escape. This is good. The temperature eventually dropped to the dew point of the more humid (moist) air trapped in the attic leading to the majority of the surfaces in your attic to 'sweat'. This is bad. As the temperature dropped further, this moisture buildup began to freeze. This is bad.

Unblocking your soffit intake vents and ensuring you have adequate ventilation for your size home is the solution. Again, I suggest contacting a professional to look at your problem as the moisture buildup that you have just found has more than likely been occurring for a while now.

I am an BSME working for a leading attic ventilation company.
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Old 01-13-2010, 05:07 PM   #14
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Major frost in attic


Here is why: http://www.energysaversny.com/frost_-_moisture

The stack effect: http://www.wag-aic.org/1999/WAG_99_baker.pdf

You need to air seal the attic from the heated moist air from below. This is the source of the frost. With your balloon framed gables, it will be a challenge. Are you comfortable working for hours in the attic, crawling around? Or rather have someone else do it? That is the first step.

Be safe, Gary
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Old 01-15-2010, 10:26 PM   #15
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Major frost in attic


I sealed the bathroom exhaust fan for now.

Got a contractor (client from work) to take a look. Yes the sofit vents are all covered with insulation. And that is preventing any airflow. He says the 2 feet of chips and insulation are actually overkill. The bathroom fan NEEDS to be fixed. He suggests pulling the insulation out of the overhangs so that I do not get icedams.

He did say that there will probably be some frost spots mostly due to the extreme cold and the dificulty of sealing a 50 year old house, but never a thick frost layer ofer the enitre roof.

So thats my TO-DO list come spring unless I feel inspired to crawl around up there in -20 temps.

It actuall reached 3 celcius for 3 days in a row....but weather man say back down to -20 by mid of next week. Just enough melt to freeze to ice for interesting driving.

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