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Old 11-25-2012, 08:52 PM   #1
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Moisture and Frost in the Attic


I believe I have an attic air circulation problem which hopefully someone can suggest ways to correct. There are water droplets forming on the protruding roof nails and in freezing weather frost on the wood.
I have a two story colonial home. The home attic area is about 900 sq. ft. The 2nd floor temperature is kept at 62 degrees F during the winter. We had both a ridge vent and continuous soffits on each side installed ten years ago. Original gable vents are blocked.
In September a layer of shingles was removed. GAF Deck Armor and 6 ft. of GAF Weather Watch to help prevent ice dams were applied. GAF Timberline HD shingles and a GAF Cobra ridge vent were installed over the entire length of the ridge.
In November-December of this year the problem started when there were quite cool temperatures in the evening here in New Hampshire. The entire roof was affected. The attic temperature was 37 degrees F and the outdoor temperature was about two degrees colder. The R factor of the attic insulation is about 50 with baffles between attic joists. There were no condensation and frost problems with the previous roof and ridge vent which I believe indicates the ridge vent was cut to the proper width.
A new bath exhaust fan is connected to a duct leading to the roof vent which is working properly and is run for 10 minutes after showering.
Some checking on line for better ridge vents found Air Vent II with a baffle which promotes better air flow was an option I am considering.
My questions are:
1. Do you think changing to the Air Vent II ridge vent would correct the problem?
2. What should the per cent relative humidity of the attic be compared to the outdoor humidity?
3. If the Air Vent II doesn’t correct the problem, what would you suggest?
4. Any thoughts of a possible roof fan controlled by a temperature/humidity control?
I greatly appreciate your valued comments. Thank you.

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Old 11-25-2012, 10:41 PM   #2
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Moisture and Frost in the Attic


Do you mean Shingle Vent II? That's what I would have used.
If they install one of those vents that comes in a roll that's most of your problum.
You say the fan runs to the roof vent, do you mean it has it's own vent on the roof that it's attached to, or is it just run to the ridge vent?

I also belive you said the soffit vents are blocked, why? Without them the ridge vent is useless.

Did anyone air seal the attic before adding the insulation. All the areas where wiring went through the top plates, around light fixtures and ceiling fans, plumbing all should have been sealed up with expanding foam before the insulation went in.

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Old 11-26-2012, 06:16 AM   #3
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Moisture and Frost in the Attic


Quote:
Originally Posted by joecaption View Post

I also belive you said the soffit vents are blocked, why? Without them the ridge vent is useless.

Did anyone air seal the attic before adding the insulation. All the areas where wiring went through the top plates, around light fixtures and ceiling fans, plumbing all should have been sealed up with expanding foam before the insulation went in.
+1

Best ridge vent in the world is useless without balanced soffits and insulation without air sealing is only partly effective.
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Old 11-26-2012, 08:17 PM   #4
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Moisture and Frost in the Attic


Hi:
I meant Shingle Vent II. The bath exhaust vents to 1-2 ft. of duct to a metal vent on the roof. The gable vents are blocked since there are soffit vents along each side of the house along with a ridge vent using a GAF Cobra vent along the entire length of the roof. As mentioned the Cobra vent may be the problem. Since it is just fiber maybe it was nailed down too much to impede the flow of air.

Since the home was built in 1969 I believe this was before the time of polyurathane foam in a can to seal all the possible escape of moisture from the living area. It appears the problem started with the installation of the new roof.

Thanks again for your time in responding to my problem.
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Old 11-27-2012, 07:07 AM   #5
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Moisture and Frost in the Attic


Air seal and insulation is a must.

If the problem started with the new roof, they over nailed the cobra vent. Get it out and get a baffled ridge vent on there ASAP.
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Old 11-27-2012, 09:01 AM   #6
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Moisture and Frost in the Attic


Thank you for your comments.

After a lot of research, I too, have always thought the Cobra vent was not installed correctly-nailed down too tight since it is nothing more than fiber.

Also, I kept a few of the GAF Timbertex ridge vent shingles which are quite heavy. I think it would be a lot heavier than a portion of a three tab shingle normally used for ridge vent shingles.

I am currently reviewing a contract to replace the Cobra ridge vent with the
Air Vent Inc. Shingle Vent II which I hope to have installed within the month.

Thanks again.
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Old 11-27-2012, 09:48 AM   #7
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Moisture and Frost in the Attic


Ventilation and insulation, that's what's causing your problems. http://reliableamerican.us/articles/...ice-daming.htm


We'll see about 50 of these same questions before the winter is over.
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Old 11-27-2012, 10:12 AM   #8
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Moisture and Frost in the Attic


Thanks for the link.

I just spoke to the contractor who is ordering the correct color GAF Timbertex ridge cap shingles and the Shingle Vent II.

Will advise as to the results which should be in the next 3-4 weeks depending on the weather.
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Old 11-27-2012, 01:21 PM   #9
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Moisture and Frost in the Attic


Frost in the attic. No kidding.

Now let me see if I have this correct. We insulate and vent with all sorts of widgets, baffles and the wrong vents that's for sale to attempt to keep the attic space air the same temperature as the outdoor ambient. From all my reading on the subject good air flow is the goal.

So now the outdoor air has reached dew point temperature, and with the correct moisture content and temperature frost forms on the roof. No surprise there. Now remember that air flow we were attempting to attain. Why anyone would be surprised to see frost in the attic is beyond me since that same present air mass is entering the attic via that good job we did venting.
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Old 12-03-2012, 08:15 AM   #10
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Moisture and Frost in the Attic


Air flow is critical but keeping the moisture out of the roof/attic assembly is just as, if not more, important.
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Old 12-03-2012, 02:32 PM   #11
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Moisture and Frost in the Attic


Quote:
Originally Posted by Windows on Wash View Post
Air flow is critical but keeping the moisture out of the roof/attic assembly is just as, if not more, important.
This is exactly true. Warm air migrating from the living space will carry with it moisture. It's physics really. Then the warm moist air will condense when it meets with the freezing timbers and sheathing. That's why we need the air flow, the best possible movement of air year round to evacuate this moisture. I see people closign their vents sometimes in the winter and that's the worst thing you can do. When I sell people attic vents I always always encourage a humidistat, because a typical attic fan with thermostat simply doesn't work in the winter time.


Furthermore, make sure no kitchen or bathroom vents dump into the attic, they carry a ton of moisture with them. The kitchen and bathroom vents should each be on a dedicated vent pipe to an external baffled vent. The habit of running a flexible duct pipe from fan to a canned/mushroom/turtle vent is a bad idea.

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