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Discussion Starter #1
So it's 10 degrees outside and 40 degrees in my attic with 80% humidity. The attic sheathing is condensing and dripping water onto my insulation. I have 10 inches of blown cellulos. I have a cap on my pull down attic stairs, and I have put great stuff foam in every gap I can find between the scond floor ceiling and attic floor(pipe chase, electrical runs, recessed lights).
How do I get the attic to be colder. The ventilation for the attic is full ridge vent and full soffit vents. By soffit vents I mean the 2 inch metal vents all along the lower edge of the roof. The vents are not blocked by insulation. More insulation or more venting?
 

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zbwmy said:
So it's 10 degrees outside and 40 degrees in my attic with 80% humidity. I have 10 inches of blown cellulos. I have a cap on my pull down attic stairs, and I have put great stuff foam in every gap I can find between the scond floor ceiling and attic floor(pipe chase, electrical runs, recessed lights).
More insulation or more venting?
I'd be looking hard for the source of the moisture first with an eye towards eliminating it. Leaky roof or flashing? Bathroom fans that are improperly vented? Leaky forced air ducts? As for more insulation or venting - given the insulation that you have and the big differential between attic and outside temperatures, I'd be looking at significantly improving ventilation and, depending on where you are, moderately increasing the insulation.
 

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Discussion Starter #3 (Edited)
PipeGuy said:
I'd be looking hard for the source of the moisture first with an eye towards eliminating it. Leaky roof or flashing? Bathroom fans that are improperly vented? Leaky forced air ducts? As for more insulation or venting - given the insulation that you have and the big differential between attic and outside temperatures, I'd be looking at significantly improving ventilation and, depending on where you are, moderately increasing the insulation.
My two bath vent fans are just stuck down in to the soffit vents. I know this is improper, but skeptical that this is the sole source of problem because we do not use them often. I read that the ridge/soffit venting can be become more inefficient by adding gable vents. I was thinking power roof vent with humidistat. Again, I still need to find the souce of problem.
 

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I have both type of vents on my house. I don't know if it's right/wrong or indifferent. Common sense tells me the more airflow the better.
 

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Is the insulation blocking your soffit (overhang) intake ventilation(extremely common with blown insulation)? Do you have enough exhaust?

What is the square footage of your attic floor? How long is your ridge line?

Definetly DO NOT mix your ventilation systems. RIdge vent and gable vent is a major NO NO. You have ridge vent that means if you want to add more vents you MUST remove your ridge vent. The ventilation systems will short circuit each other and be counter productive. If you have gable vents and a ridge vent, close the gable vents from the inside of the attic.
 

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Discussion Starter #6
Grumpy said:
Is the insulation blocking your soffit (overhang) intake ventilation(extremely common with blown insulation)? Do you have enough exhaust?

What is the square footage of your attic floor? How long is your ridge line?

Definetly DO NOT mix your ventilation systems. RIdge vent and gable vent is a major NO NO. You have ridge vent that means if you want to add more vents you MUST remove your ridge vent. The ventilation systems will short circuit each other and be counter productive. If you have gable vents and a ridge vent, close the gable vents from the inside of the attic.
That is what I heard too. Do not add gable vents to a ridge/soffit system. Thanks for confirming.

The insulation is not blocking the soffits. There are those styrofoam things(can't remember the name), installed to prevent that.

What do you mean by enough exhaust?

The roof is 36 feet long, so I assume the ridge vent is approx. the same.

My attic floor is 24x36ft. 864 sq./ft. ?

There is no vapor barrier between the insulation and the sheet rock ceiling below. I read a vapor barrier is not required with blown insulation. The cellulos acts as it's own barrier. Is this true? I was thinking about that ceiling paint thats available that acts as a vapor barrier.
 

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Are you sure the roof has felt under the shingles? I've seen roofs facing north in the winter with no felt create swiming pools and bath tubs.

Bob

zbwmy said:
That is what I heard too. Do not add gable vents to a ridge/soffit system. Thanks for confirming.

The insulation is not blocking the soffits. There are those styrofoam things(can't remember the name), installed to prevent that.

What do you mean by enough exhaust?

The roof is 36 feet long, so I assume the ridge vent is approx. the same.

My attic floor is 24x36ft. 864 sq./ft. ?

There is no vapor barrier between the insulation and the sheet rock ceiling below. I read a vapor barrier is not required with blown insulation. The cellulos acts as it's own barrier. Is this true? I was thinking about that ceiling paint thats available that acts as a vapor barrier.
 

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Discussion Starter #8
Glasshousebltr said:
Are you sure the roof has felt under the shingles? I've seen roofs facing north in the winter with no felt create swiming pools and bath tubs.

Bob
Yes

New roof 5 years ago. Saw the paper being put down. Two rows of ice and water shield also.
 

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Discussion Starter #9
one suggestion was to just add more soffit vents in the eaves. Putting one every third bay or so. I am skeptical. I read where the air intake was supposed to be 50% and the air exhaust 50% to get the flow. Won't adding more intake disrupt this calculation and stagnate the floe even more?
 

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Discussion Starter #12
No attic fan
I have drip edge vent two sides 36'x9sq" per foot right?
Cobra ridge vent 36' x 18sq"/foot right?
attic floor 24'x36' = 864 sq feet
Is this enough?
 

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This sounds like a condensation problem that an attic fan will fix. They cost about $80 but you need to cut a hole in the roof, tighten up the roof shingles around the new vent, seal all terminations with roof sealant and do some minor electrical work. I would rate the difficulty to complete this project, on a scale of 1-10 an 8.

rfs
 

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Discussion Starter #14
EIFS101 said:
This sounds like a condensation problem that an attic fan will fix. They cost about $80 but you need to cut a hole in the roof, tighten up the roof shingles around the new vent, seal all terminations with roof sealant and do some minor electrical work. I would rate the difficulty to complete this project, on a scale of 1-10 an 8.

rfs
Thats what I was thinking but some are saying when I turn it on I will only be drawing from the ridge. And when the fan is off the ridge may draw from the fan and not the soffits, therfore reducing my airflow.
 

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zbwmy said:
some are saying when I turn it on I will only be drawing from the ridge. And when the fan is off the ridge may draw from the fan and not the soffits, therfore reducing my airflow.
I don't know if you've been following the other threads but here's a link to some info on attic ventilation:
http://airvent.com/professional/whyVent/evaluate.shtml

Amongst other things that site reccomends "Don't use a combination of different types of exhaust vents, like power vents with ridge vents. In this case, competing vents pull air from each other instead of soffit vents."

I will tell you that the house I live in has gable vents on each end (triangular shaped, about 54" across the base and 30" high), does not have a ridge vent, and has a power exhaust fan that runs only in high heat seasons. My soffits are vented albeit poorly I think. I have (2) bathroom fans that vent directly into the attic and they have backdraft "flaps" that close when the fans are off. The attic floor has a paper vapor barrier over the drywall beneath with about 10" of fiberglass batting over it. I've never seen any sign of excess moisture accumulation or mold formation in the attic.
 

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vent boxes

I just blew in 16 inches of cellullose in the attic of my new house. The vent boxes are whatever they are called were not designed properly to hold back cellullose because there was still a gap above the sill plate where the cellullose could fall into the soffit. They do work pretty good for fiberglass, which I did not want. What I did was take 4x8 foot sheets of 1/2inch tuff-r, the foil backed insulation used for pole buildings, cut it in half to 2x8 sheets, notch them out so they slid over the ceiling truss, forming a tight vent box that reached all the way down to the sill plate. I tacked this 2x8 sheet to the roof truss, forming a large box the full depth of the 2x4 inch roof truss, all the way down to the sill plate. If i would have used the "things" the building supply outfit sold me, I would have filled my soffits with cellullose. Even with this tall homemade box, I had to blow the cellullose in piles and carefully rake it up to the edges roof trusses so it would not blow over the top of the soffit guard.

I have no idea why they are selling these prefab soffit guards with anything other than fiberglass, but they wont work with cellullose being blown in. I would check your soffit again, my guess it is plugged unless you bought something a lot better than I did.
 

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Discussion Starter #17
Grumpy said:
When it comes to intake it is better to error in favor of too much. Infact there really isn't such a thing as too much intake. The ventilation system will only allow as much fresh air in as the exhaust vents can put out.
Still having moisture problems. Staining on bedroom ceilings now. I had a contractor come take a look, he seems stumped. I asked if putting more soffit vents in to supplement the drip edge vent would help move more cold air. He said it may just create a vorticy between the drip edge vent and new soffit venta and do more harm. He is concerned the the cobra ridge is clogged with dust or something.
 

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I agree with him that if you have a drip edge vent you probably wouldn't want to put in soffit vents... But if it were my house or project I wouldn't have used the drip edge vent in the first place. I'd have created the soffit vents. You can create much more air flow with a soffit vent, than the drip edge vent. Also the drip edge vent can easily become clogged, ESPECIALLY if you have a gutter.

The cobra vent can become clogged but it's not likley. It's easy to check and clean if necessary.

You have a 860 sq ft attic. You need minimum 27' of ridge vent, with EQUAL intake ventilation. You'd need a minimum of 9 16"x8" soffit vents or 54' of continuous soffit vent, or 54' vented drip edge. You said you have 36' of drip edge vent?!

Did you ever check your attic for draft? Using a cigarette lighter and watching the flame is a good way. Be careful not to hold it near anything flammable. If there is a draft the flame will flicker.

If you install an attic fan you MUST remove the ridge vent. $80 is way WAY cheaper than I'd charge to install. The fan is about $50 at the store for an 1170 CFM (medium duty), which is what you'd need for your attic. Also if you do install a fan, most manufacturer's recommend upgrading your intake ventilation or the motor will burn out. In this case you'd need 14 16x8 vents or 86' of soffit/drip vent.
 

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Discussion Starter #19
Grumpy said:
I agree with him that if you have a drip edge vent you probably wouldn't want to put in soffit vents... But if it were my house or project I wouldn't have used the drip edge vent in the first place. I'd have created the soffit vents. You can create much more air flow with a soffit vent, than the drip edge vent. Also the drip edge vent can easily become clogged, ESPECIALLY if you have a gutter.

The cobra vent can become clogged but it's not likley. It's easy to check and clean if necessary.

You have a 860 sq ft attic. You need minimum 27' of ridge vent, with EQUAL intake ventilation. You'd need a minimum of 9 16"x8" soffit vents or 54' of continuous soffit vent, or 54' vented drip edge. You said you have 36' of drip edge vent?!

Did you ever check your attic for draft? Using a cigarette lighter and watching the flame is a good way. Be careful not to hold it near anything flammable. If there is a draft the flame will flicker.

If you install an attic fan you MUST remove the ridge vent. $80 is way WAY cheaper than I'd charge to install. The fan is about $50 at the store for an 1170 CFM (medium duty), which is what you'd need for your attic. Also if you do install a fan, most manufacturer's recommend upgrading your intake ventilation or the motor will burn out. In this case you'd need 14 16x8 vents or 86' of soffit/drip vent.
The house is 36 ft. long, so I have 72 ft. of drip vent. 36x2=72 ft.
I checked the draft with a lighter but I left the pull down stairs open and I think I need to do it over with them closed.
If I did install a fan how would I add more drip edge, it covers the whole length of the house.
Either way it sounds like i'm stuck till spring.
 

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Discussion Starter #20
The first contractor who has looked at this attic states the cobra vent I have is known for it's poor performance and suggests replacing with an AIR VENT II ridge vent. He also states that the cut away on my roof sheathing at the ridge pole does not seem to be very large and would increase this gap when putting in the AIR VENT II.

This to me seems like a good first step to trying to pinpoint the cause of the humidity. Obviously I will be continuing to seal all air leaks in attic floor also.

How much should it cost to take of the cobra and put in the new 36 foot AIR VENT II?
 
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