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Old 04-07-2009, 10:39 PM   #1
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I am ready to get rid of the ridge vents


I live in the northeast & have problems with ice dams. I had a roofer come out & state that I have ineffective ridge vents. That is apparent to me as we got two feet of snow in one week and it took several weeks for the snow to melt off the ridge vents.

I am reroofing and putting in dormers. The footprint of heated section of the house is 50' x 70'. My thought is to close off the linear 70' of ridge vents and put in 3 gable vents. Each gable vent would ventilate ~ 1/3 of the attic. Each 1/3 of the attic would have no air connection to the rest of the attic. Each gable vent area would be 9 to 16 ft2 and would give ~ 90:1 gable area:roof area. The roof slope is as low as 4:12 and every air channel has at least a section of cathedral ceiling it must pass through. The soffit vents are continuous and are 30:1 to 40:1 soffit area:roof area.

Does this make sense? The gable area would be 1/3 that of the existing ridge vent area but if the ridge vents don't work when I need them most (winter) why not get rid of them? The summer is not as much of an issue as the roof is well insulated (R30-R50) and shaded by trees. Thanks

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Old 04-07-2009, 10:43 PM   #2
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I am ready to get rid of the ridge vents


I have a dormered Cape w/ridge vents & soffit vents
No problems near the ridge this past winter
But I did have snow on the roof for long spells

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Old 04-07-2009, 11:16 PM   #3
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I am ready to get rid of the ridge vents


What brand of Ridge Vent do you have on your home currently?

Does it look like a rolled up brillo pad or furnace filter?

I tried many brands, but found faults with all except for the Shingle Vent II and a knock-off made, called Snow country seems it would be very similar too.

Never a problem since I switched to using that brand exclusively in 1993.

Ed
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Old 04-08-2009, 11:06 AM   #4
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I am ready to get rid of the ridge vents


I have Cor-A Vent installed in 1992. It looks like the V400E.

I called up Air Vent Inc. and they stated their product (Shingle Vent II) doesn't work under snow and recommended I get a power vent. Maybe the sales lady didn't know what she was talking about?

In any event I don't have issues with snow getting inside the house. Isn't that the purpose of those snow ridge vents? How can one brand of ridge vent melt a hole in the snow above it and the others not?

I was off by a factor of 12 with my soffit vent calculations. It looks like my roof area: soffit area is 350:1, well below some references that say you need 150:1 for a 4/12 roof. Perhaps running another continuous strip of soffit vents? There is room for it.

When you have 8 foot long icicles hanging from your house you got to do something about it. Perhaps continuous soffit and ridge vents were never designed for roofs where it is 30 feet between the soffit and the ridge.
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Old 04-08-2009, 08:09 PM   #5
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I am ready to get rid of the ridge vents


There is no reason you can't have both ridge vents and gable vents.

http://roofingcontractorreview.com/R...ntilation.html
http://roofingcontractorreview.com/R...cuit-Myth.html

How's your insulation?

And make sure your soffit vents are clear.

http://roofingcontractorreview.com/S...ntilation.html
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Old 04-08-2009, 09:53 PM   #6
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I am ready to get rid of the ridge vents


I agree that the combination of ridge vents and gable vents will not "short circuit" the heat removal. My concern is that if you have a rainy, windy day with the wind blowing at the gable vent, the gable vent will act as an inlet and the ridge vents as an outlet. You could get water coming in the gable vent from the air coming in. I guess if you put a pan directly inside the gable vent, even if you get rain coming in, it would just collect in the pan and eventually evaporate.

You could also have inlets & outlets between gable vents. I am going to segregate the attic into 3 parts, each with its own gable vent so one doesn't act as an inlet to the other.

The house was built with R30 insulation. The reason I think my ice dams are worse than others is because of all the air leaks. (11 recessed lights leaking air, visibly discolored fiberglass around leaks in drywall). Insulation does not block any vents. So my plan is to seal the leaks and increase ventilation on the half the house that I am not redoing. That means a gable vent and more soffit vents on that section.

On the half that I am redoing I will have R40 to R50, scrupulous air sealing and 150:1 attic area to vent area. The sections I am redoing either have peaks that are 4:12 sloped or 17:12 sloped (gotta love those architects) which is close to the limits for ridge vents. My biggest hesitancy to putting in gable vents is I don't see anyone doing it in new construction.
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Old 04-09-2009, 09:52 AM   #7
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I am ready to get rid of the ridge vents


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Originally Posted by PerpetuallyRepairing View Post
I agree that the combination of ridge vents and gable vents will not "short circuit" the heat removal.

My biggest hesitancy to putting in gable vents is I don't see anyone doing it in new construction.
Dennis of DMC is a vigilant defender of the premise that short circuiting does not occur, which goes contrary to significant theory espoused by ventilation building science.

Admittedly, there are no available specific studies that prove the theory, but I have been in discussions with many home owners and home inspectors on many forums that show otherwise.

For new construction, maybe the architects have finally discovered that the designed air flowage does not work, or that they just found a cheaper method to provide the minimum code criteria.

I would still advise against it, but it is your decision.

Somewhere on this and other forums, I have visual proof that the Shingle Vent II Ridge Vent performs even when a fresh 14" snow fall has occurred, which shows quite clearly that the new fallen snow has melted at the ridge vent exhaust portals, while keeping the main pack of snow on the remainder of the roof surface, eliminating the typical icicle formation and ice damming problems that had been prevalent previously.

I will see if I can find which thread topic those are posted in and post them here later tonight or tomorrow.

Ed
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Old 04-09-2009, 10:07 AM   #8
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I am ready to get rid of the ridge vents


I would not mix a ridge vent & gable vent with soffit vents
Air will be pulled from the area of least resistance - the gable vents
Why would you want to decrease the air flow under the roof deck?
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Old 04-10-2009, 08:50 PM   #9
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I am ready to get rid of the ridge vents


Okay, I guess I will enter the debate and make some dogmatic statements. I've got a degree in fluid mechanics and spent decades doing consulting in the field. As long as you have soffit vents, short circuiting does not occur with the combination of ridge and gable vents. The buoyancy of the hot air forces the hot air out regardless of the exhaust vent configuration. Continuous soffit and ridge vents have the advantage of creating a more uniform attic temperature as the air flow is more uniform. It would be possible to get areas of the attic that remain relatively hot with a single gable vent. Every case is different. You have to look at flow resistances of different air paths and the overall buoyancy force of the attic. To be really fancy you can model the whole attic on the computer. In my case I am going to try gable vents because the cathedral ceilings even out the air flow before it gets to the open attic at the ridge.

If what you say about Shingle Vent II is true, it's too bad the manufacturer hasn't taken the time to figure out why. I still can't see how if once the vent is clogged with snow, one brand will melt a path faster than another. At that point the melting happens by conduction.
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Old 04-10-2009, 09:56 PM   #10
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I am ready to get rid of the ridge vents


Yup hot air rises
And where will it draw cool air from?
The rdige vent near the sides will draw from the closest opening - the gable

Thus decreasing air flow along the roof deck to some degree
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Old 04-11-2009, 09:26 AM   #11
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I am ready to get rid of the ridge vents


Quote:
Originally Posted by PerpetuallyRepairing View Post
If what you say about Shingle Vent II is true, it's too bad the manufacturer hasn't taken the time to figure out why. I still can't see how if once the vent is clogged with snow, one brand will melt a path faster than another. At that point the melting happens by conduction.
I show my customers photos of the true real life results that I have seen, so I know that it is true.

I appreciate the technology that computer aided simulations can provide, but would they be accurate to precise environmental conditions, or GIGO?

I really need to get those photos posted for you.

Ed
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Old 04-11-2009, 09:52 AM   #12
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I am ready to get rid of the ridge vents


Quote:
My concern is that if you have a rainy, windy day with the wind blowing at the gable vent, the gable vent will act as an inlet and the ridge vents as an outlet. You could get water coming in the gable vent from the air coming in.

I don't think that would be much of a concern.
a. Airflow against the gable end of a building will push up and around the the building. Not necessarily into the gable vent.
b. A well designed gable vent should prevent blowing rain from entering the attic.
Take a look at this video.




Scuba,
The closest vent would not be the path of least resistance. The same forces acting on the ridge vent affect the gable vent.
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Old 04-11-2009, 09:58 AM   #13
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I am ready to get rid of the ridge vents


Quote:
My biggest hesitancy to putting in gable vents is I don't see anyone doing it in new construction.
You also don't see hot dipped galvanized nails, soldered copper flashings, 30lb (not#30) tar paper, lead stack flashings, etc.
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Old 04-12-2009, 01:06 PM   #14
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I am ready to get rid of the ridge vents


Hi,

Hot air rises. You can not short circut that. No matter how hard you try.

Hot air will rise.
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Old 04-12-2009, 09:05 PM   #15
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I am ready to get rid of the ridge vents


Yeah, tell that to Mother Nature

I was at the MIL's house today
Strong wind blowing in - straight thru the gable
Strong enough to stop any air rising up thru the soffits
Real world.............

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