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Old 08-20-2012, 12:09 PM   #1
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new cool vent roof; close gable vents?


I have an old 1 3/4 story home in snowy Minnesota. Ice dams form every winter due to no soffits and too little room for insulation above the slanted part of the walls.

This spring I had a Hunter cool-vent panel roof installed. The original shingles were torn off, then a vapor barrier was laid topped by the panels, then a second vapor barrier, ice and shield, and shingles. The cool-vent panels are composed of rigid foam with an air passage above topped by a plywood deck. The edge of the roof is vented into the panel gap and a ridge vent runs across the top. This should keep the heat away from the roof and eliminate the ice dams.

What should I now do with the enclosed attic space? It has a mixture of insulation on the floor (no vapor barrier) and 4 small gable vents, one at the top of each wall of the attic. Should I close off the gable vents or leave them open?

If I leave the vents open, will the cold air cause condensation? Will the vents just pull more warm air from below into the attic? Will they vent enough warm air to keep the attic dry?

If I close off the vents, what happens to any moisture that enters the attic?

Any advice would be greatly appreciated!

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Old 08-20-2012, 12:20 PM   #2
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new cool vent roof; close gable vents?


A ridge vent is useless if there's also gable vents.
All it will do is suck air in the gables and reliece it out the ridge.
Having a cold attic does not cause ice dams. The heat escaping from a poorly insulated ceiling envelope and not having the ceiling air sealed causes the snow to melt during the day which freezes at night.
There's not suppost to be any insulation in the roof over hang area, only over the ceiling area.

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Old 08-20-2012, 01:12 PM   #3
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new cool vent roof; close gable vents?


Thanks for the reply. Air enters at the ventilated edge along the eaves and exits the ridge vent through the air channel in the roof panels. This is above the original roof deck and separate from the attic. The attic is now enclosed from the outside except for the gable vents. Should I close the gable vents?
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Old 08-20-2012, 05:16 PM   #4
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new cool vent roof; close gable vents?


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Originally Posted by MNhome View Post
I have an old 1 3/4 story home in snowy Minnesota. Ice dams form every winter due to no soffits and too little room for insulation above the slanted part of the walls.

This spring I had a Hunter cool-vent panel roof installed. The original shingles were torn off, then a vapor barrier was laid topped by the panels, then a second vapor barrier, ice and shield, and shingles. The cool-vent panels are composed of rigid foam with an air passage above topped by a plywood deck. The edge of the roof is vented into the panel gap and a ridge vent runs across the top. This should keep the heat away from the roof and eliminate the ice dams.

What should I now do with the enclosed attic space? It has a mixture of insulation on the floor (no vapor barrier) and 4 small gable vents, one at the top of each wall of the attic. Should I close off the gable vents or leave them open?

If I leave the vents open, will the cold air cause condensation? Will the vents just pull more warm air from below into the attic? Will they vent enough warm air to keep the attic dry?

If I close off the vents, what happens to any moisture that enters the attic?

Any advice would be greatly appreciated!
If the attic space is enclosed, it needs to be treated as conditioned. Venting above the roof deck will do nothing to control moisture through the attic unless the spaces are connected. It will only help with the ice dams.

You need to air seal the attic floor regardless to keep the air loss and moisture to a minimum.

Who's idea was the vented roof panels?
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Old 08-20-2012, 05:35 PM   #5
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new cool vent roof; close gable vents?


I assume I should close the gable vents then. How would you go about air sealing the floor?

One of the roofers I called for an estimate proposed the vented panels. The other contractors wanted to spray foam between the rafters. There is very little room between the inside ceilings and the roof deck to spray foam and/or ventilation chutes, so I went with the vented panels on top.

I do not want to disturb the insulation on the attic floor because the bottom layer has vermiculite (which may have asbestos). Wouldn't any barrier on top of the insulation trap moisture?

Thanks for the help!
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Old 08-20-2012, 05:43 PM   #6
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new cool vent roof; close gable vents?


No. Do not close the gables.

Venting above the roof deck, unless it is connect to the attic, is not going to do anything to control moisture.

Your roofer dropped the ball on this one.

Did he remove the original roof deck? Is the venting on the panels connected to the attic?

I suspect not and if you close up those gables, you are going to have a moisture trap like you won't believe.

The roof deck should have been spray/rigid/combination foamed if you wanted to go to a hot/insulated roof deck or you should have air sealed and insulated the attic more thoroughly.

Proper air sealing and repair of the ventilation would fix the ice dams too.

You may have fixed the ice dams in a round about sort of way with the vented roof deck, however, you have done nothing to control the moisture.

Closing off the gables in this case is a big no-no.
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Old 08-20-2012, 06:19 PM   #7
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new cool vent roof; close gable vents?


Ouch!

No, the original deck was not removed.

You are correct. The attic is not connected to the roof ventilation, which is why I'm concerned about the now enclosed attic. I can't undo past decisions. What are my options?

Would you try to connect the attic to the new ventilation i.e. punch holes through the original decking, vapor barrier and foam? This will very likely void my roof warranties.

(The old roof had a few small turtle vents along the top ridge, no soffits/intake, and the four gable vents. We haven't had condensation problems in the past - if that helps.)

This is down right depressing!
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Old 08-20-2012, 07:01 PM   #8
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new cool vent roof; close gable vents?


The fact that you have a vapor barrier not installed may exacerbate the problem were as it was not a issue previously.

Regardless, it is not that big an issue if you vent the attic.

The roof should remain vented and air sealing the top plates and penetrations will help a bunch as well.
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Old 08-20-2012, 07:40 PM   #9
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Okay, I should leave the gable vents open and try to further seal attic bypasses as best I can. Would you take any further action?

I haven't paid the roofer yet. Is there anything I should request before I do?

Thanks again for your time!
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Old 08-20-2012, 08:19 PM   #10
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new cool vent roof; close gable vents?


That should be good.

Tell the roofer to study up on ventilation for future clients.

Hop over to the insulation forum and start looking at the air sealing part of the equation.
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Old 08-20-2012, 10:50 PM   #11
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new cool vent roof; close gable vents?


I am a Chicago-suburbs roofer. We dont get the same snowfall a you but we get enough. I have never installed the hunter system, but reading their install guide: http://www.hpanels.com/images/storie...Guide_real.pdf
It appears to specify that there should be a synthetic underlayment used under the shingles and an unnamed "vapor barrier" applied under the hunter system. It itself has a eave and ridge vent system specified-which you said that he used. I guess im saying that as long as the installer was factory trained and he installed it per the mfr specs you are fine.

MNHome: all we as un-certified, non-users of the system are doing is second guessing that which we didnt install, are not trained to install and may not understand.

As to the ventilation of the attic, my OPINION is to leave the gable vents to vent humidity, as the hunter system should be reducing your attic temp but does NOTHING that I can see to eliminate the humidity that migrates thru your ceiling, insulation and into your attic. A great resource for honest intelligent opinions on attic ventilation is a vent company like AirVent- www.airvent.com they are not a shingle manuf so they dont have a spin-ask for Paul.

As to air-sealing the attic floor I say NO! that will stop the moisture, creating a turkish bath for all things bad and moldy on the house side. Your best bet in my opinion is simply more insulation to be installed to an r-value dictated by your climate.

Rob Michael
www.rjmbuild.net

Last edited by RJM Build; 08-20-2012 at 11:02 PM. Reason: bad grammar-hey im a roofer, not an english teacher!
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Old 08-21-2012, 07:54 AM   #12
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new cool vent roof; close gable vents?


RJM,

I take issue with system then in this case.

The idea of above deck venting is great but the manner in which it is installed a represented will not change the venting of the attic and will create confusion just as it did in this case.

The synthetic underlayment is a Class I vapor retarder in this case so that moisture going up to the roof deck has no where to go.

Before offering any additional advice on air sealing, I think you should do a bit more research. Moisture control is critical and should be controlled via production limits (i.e. humidifier settings, aquariums, indoor plants, etc) and proper venting (i.e. bath fans, range hoods, etc) through the roof deck an straight to outside.

Leaving the building envelope across the attic floor unsealed to move moisture is not the proper approach and I have never seen a moisture issue in a home after air sealing if the moisture was previously controlled. Most homeowners will just wind up turning down their humidifiers or off altogether.
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Old 08-21-2012, 08:28 AM   #13
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new cool vent roof; close gable vents?


RJM, thanks for the links! I read through the Hunter panel manual and as much as I can tell from the ground, my roofer followed the directions. He used GAF Tiger Paw synthetic underlayment on top of the original roof deck and on top of the new plywood deck of the panels.

I agree, the new roof does nothing for ventilating the attic, which now has a vapor barrier above it and no roof venting. The roofer recommended and the contract states that he will close the gable vents that are now the only source of outside air to the attic. The roofer is now having second thoughts and it's up to me to decide whether the gable vents are closed or not.

The original thought was the new foam insulation on the roof would keep the attic warm and the attic would essentially become part of the interior space. If left open, the gable vents would introduce cold air (which could cause condensation) and pull heat out of the interior of the house. But I think if I close them, moisture will have no avenue of escape except slowly through the uninsulated stucco attic walls - maybe too slowly to prevent mold growth.

And for all I know, the gable vents may not be enough.

But I need to tell the roofer what to do!

Windows on Wash - at least I don't use a humidifier and I shower in the basement with the fan running.
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Old 08-21-2012, 08:42 AM   #14
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new cool vent roof; close gable vents?


There is not near enough insulation in those panels to qualify is a conditioned/insulated roof.

Air seal the floor, leave the gables open (based on what you have existing).
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Old 08-21-2012, 09:21 PM   #15
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Windows is correct; air-seal the attic floor- all wiring/plumbing penetrations, chases, around flue exhausts with suitable fire-safe materials, attic access hatch; http://www.google.com/url?sa=t&sourc...wWATQw&cad=rja

If you go the Hunter route, you are required to use R-25 for Zone 6, R-30 for Zone 7---- that is the polyiso thickness above the old roof deck. THEN, add fibrous (or other) insulation below the roof deck sheathing from inside the attic with a vapor retarder to meet your R-value total R-49 http://publicecodes.cyberregs.com/ic..._11_sec002.htm

, removing any vapor retarder/barrier-poly that is on the attic floor; http://resourcecenter.pnl.gov/cocoon...r/article/1520

If the Hunter Polyiso is not minimum R-value per code, add a foamboard = air-impermeable thickness required (plus canned foam to air seal) under the sheathing, and a filler insulation per minimum code for your location. This would be without a vapor retarder on the rafter bottoms, but requires an air barrier= drywall or housewrap approved by your local AHJ.

Picture; fig. 3; http://www.buildingscience.com/docum...archterm=attic+

Close the gable vents and the soffit vents, after you air seal the attic floor, remove any v.r. or v.b. on attic floor. How thick is the vermiculite?

Condensation risk for Zone 6, 7 in Table 3, and especially #4; http://www.buildingscience.com/docum...d-roof-systems

Gary
P.S. I read your thread again, no v.b. on floor, to tired to change my typing, and there was a great Code link …LOL

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