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Old 08-21-2012, 02:34 PM   #1
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Add Ridge Vent?


Hello All!
I have a dilemma regarding my asphalt shingle roof replacement. The roofer wants to add a ridge vent and close off my 4 large gable louvers. The problem is, I have a 36” whole house fan, and based on my calculations, the ridge/soffit vents will not provide adequate exhaust.


My 39 yr old house is a 80’ x 26’-4” brick ranch with a 8:12 slope, approx half shaded by oak trees. It has a 3’ higher roof in the center with 2 gable louvers, and a gable louver on each end of the low roof, with one turbine on the low roof (why??). Attic has continuous floor.

With the (4) large gable louvers, (42) 16x4 soffit louvers, and single turbine, I have about 3450 SI of ventilation, or roughly 1 SF for every 100 SF, more than adequate! It is drawn in CAD, so I can easily calculate. The attic SF is approx 2400 SF.

Temp measurements during the day revealed 90 deg outside and 99 in the attic high roof, not bad. It hits 95-100 quite often in the summer in NC. I have two options:

OPTION 1: Add 84’ of ridge vent and possibly (12) more 16x4 soffit louvers to get a 50/50 balance, and close off the large gable louvers and remove turbine fan. This would be approx 2900 SI of overall ventilation (less than what I have now).

I would need to have the plywood over at least two louvers easily removable so I could use the whole house fan in the spring and fall. Also, while the louvers are open, they would short-circuit the ridge/soffit vent on the high roof 3-4 months a year.

OPTION 2: Keep what I have, and add two more turbine fans to the high roof. When it was 99 deg at the high part of the attic, my power fan at the low roof louver set at 95 deg had not yet come on. It only comes on when it is ~95 outside. It does work.

Cliff notes: the 2400 SF attic is currently well ventilated and pretty cool, worked well for 39 yrs. But it is not “cutting edge” with ridge vent system, which would actually reduce the overall ventilation SF, but make it a more consistent temp. But not easy to use whole house fan.

Also, is it possible that low roof ridge vents could turn into intakes for the high roof ridge vent? Low roof is 3 ft lower and offset about 4 ft from high roof.
I am leaning towards option 2.

Thanks!
Al


Last edited by AlleyG; 08-21-2012 at 02:38 PM.
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Old 08-21-2012, 03:12 PM   #2
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Add Ridge Vent?


Put in the ridge vent.

Leave the gable vents but close them off with covers in the winter months.

Whole house fan is only getting run in the cooling season anyway. The short circuiting of the ridge at that point is less of an issue.


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Old 08-21-2012, 03:44 PM   #3
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Add Ridge Vent?


Make sure to check with the shingle manufacturer on this issue.
You can void your warranty if everything isn't done to their specs.
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Old 08-21-2012, 05:16 PM   #4
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Quote:
Originally Posted by chb70 View Post
Make sure to check with the shingle manufacturer on this issue.
You can void your warranty if everything isn't done to their specs.
Thanks for pointing that out. I didn't clearly express my opinion.

My recommendation would be to put the ridge vent in and just close off the gables in the winter.
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Old 08-22-2012, 08:04 AM   #5
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Damn, I was hoping someone would vote for option 2!

Like I mentioned, the attic is currently well ventilated for only having gable louvers as they are very large. I cant help but think it would be hotter up there replacing 4 large louvers with a skinny 1 1/2" slot in the ridge.

I was in the attic last night, and noticed it would be a PITA to remove a plywood cover over the louvers as they are pretty high off the floor.

I think this comes down to ridge vent VS whole house fan. If I add the ridge vent, might as well take the whole house fan out of service, which is a drag even though I cant use it much in our humid climate.

I would love to see a test where the attic temp was checked before and after changing from louvers/soffit vent to ridge vent/soffit vent, in an attic that was relatively cool to start.

Thanks,
Al
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Old 08-22-2012, 09:33 AM   #6
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Add Ridge Vent?


Whole house fans do work, but as you mentioned, only in the right conditions and if they are not sealed off when not in use, they just leak a bunch of conditioned air into the attic.
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Old 08-22-2012, 10:41 AM   #7
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I made a cover to put in place of the whole house fan louver during the "off" months. Has rigid insulation behind it.

Al
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Old 08-22-2012, 09:49 PM   #8
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That is good. You are ahead of the game.
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Old 08-23-2012, 12:09 AM   #9
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With your 42 intakes (@25sq.in. each), if balanced to exhaust, 1/165. With the 3' minimum stack height, is there a vapor barrier on attic floor at drywall? Is that a whole house fan ducted directly to the house or an attic exhaust fan?

Where are you located?

Gary
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Old 08-23-2012, 08:36 AM   #10
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No vapor barrier on attic floor, unless you count the backing on the insulation. The whole house fan blows directly into the attic. It is an older belt driven Westinghouse unit, cannot find any info on it, but similar fans are ~6900 CFM. It is a beast, with 3-4 windows open, it will still suck open the porch door if you just turn the knob!

The fan is why I am trying to keep the large gable louvers, and have 3-4 turbines, in lieu of the ridge vent.

I am in Raleigh, NC. Hot and humid in the summer!

Thanks,
Al
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Old 08-24-2012, 10:37 PM   #11
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So you are blowing air (pressurizing) into the attic being replaced by humid outside air from below (because it is over-powered) the leaking walls and floors, possibly crawl space/basement (depressurizing). (confused myself on that one, it's late, I'm tired, etc. LOL) http://www.conservationtechnology.co...eakagePathways

As this moisture moves through your walls, floors, chases, windows, it goes into the attic through wiring/plumbing holes to deposit moisture on the roof framing before exiting at the fan...http://www.google.com/url?sa=t&sourc...wWATQw&cad=rja

it should be ducted from the rooms below to the fan, directly to outside. Size it correctly; http://www.homeenergy.org/show/artic...page/4/id/1534

Inspecting; http://www.homeenergy.org/show/artic...page/2/id/1360

Eye-opener; http://www.advancedenergy.org/buildi...%20Studies.pdf

Back-drafting; http://www.nachi.org/attic-ventilati...s-part1-25.htm

Exterior pictures of the house/roofs would help; http://www.diychatroom.com/f98/

Gary
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Old 08-25-2012, 06:45 AM   #12
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It is the whole house fan. I open 3 or 4 windows and let er rip! I only turn it on when it's cooler and dryer outside than inside.

Yes it blows directly into the attic but I have 4 large louvers to allow it to exhaust. It is a great system but I can only use it 3 or 4 months a year around here.

Al
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Old 08-25-2012, 07:17 AM   #13
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Despite the older engineering, whole house fans work just fine if used properly and it sounds like you are doing so.
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Old 08-25-2012, 07:37 AM   #14
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This is why I am trying to avoid closing off the 4 louvers and adding a ridge vent. Upon closer inspection it would. be too much work to take the louver covers off every summer.
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Old 08-25-2012, 05:10 PM   #15
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Add Ridge Vent?


You've got a system your roofer doesn't fully understand. It probably wouldn't hurt anything to add the ridge vent (and it might not help in this situation), but leave the gable vents open no matter what if you still intend on using the whole house fan.

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