# ridge vent / gable vent help



## enforcer (Aug 25, 2008)

i see many opinions. however, IF THE GABLE VENTS ARE REMOVED after putting in ridge vents, can that cause any harm ? or is removing the vents just a waste of time at that point?
what about removing the vents but keeping the attic fan ?


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## Framer53 (Feb 23, 2008)

I have always removed the gable vents when I install new ridge vents.

Having said that, I have found nothing in the lit. anywhere that says it is imperative to do so.

I have never liked powered vents, exception being is if I lived in the south. My opinion is they are highly unnecessary for most applications.


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## Framer53 (Feb 23, 2008)

Ed the Roofer said:


> The ventilation manufacturers and most widely accepted ventilation studies and theories show that the gable vent air flowage would interfere, also know as Short-Circuit the current soffit to ridge ventilation flowage.
> 
> It is a recognized short-coming by mold remediation companies that by having competing types of upper air exhaust systems, the probability of mold growth is increased and is recommended to cover up the gable vents when their is a properly functioning soffit intake flowage and ridge vent exhaust flowage already in place.
> 
> Ed


Any links to back this up Ed?
I believed as you, but haven't found any back up from Building Science.


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## dennis (Nov 17, 2004)

[QUOTEI always wanted to do a similar experiment when
this argument first came up but figured that actual,
real life conditions would be hard to duplicate and 
control.][/QUOTE]

I agree. We can design the perfect house on paper, but it may not look anything like what gets built. One size does not fit all. 
The videos are not perfect scientific studies, but I think they illustrate the basic concept. I will leave it to better minds to figure out the humidity problem.



> i see many opinions. however, IF THE GABLE VENTS ARE REMOVED after putting in ridge vents, can that cause any harm ? or is removing the vents just a waste of time at that point?
> what about removing the vents but keeping the attic fan ?


That depends. If you live near me, your ridge vents could be covered in snow for weeks at a time and the additional gable vents are a plus. If you have a mcmansion with hips and short ridges,or live in the south, the attic fan would be a plus.


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## greg24k (May 19, 2007)

The gable vent is usually closed off when there is soffit and ridge vent system. If you have a ridge vent, it might draw the air from the gable and not from the soffit, and being gable vent considered to be the worst attic ventilation source, you could have some serious problems.

Take a wood burning fireplace for instance. When you burn the fireplace, it takes all the heat from the room out. If you crank a near by window, it will draw the cold air in, leaving the hot air in the room.:thumbsup:


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## Framer53 (Feb 23, 2008)

greg24k said:


> The gable vent is usually closed off when there is soffit and ridge vent system. If you have a ridge vent, it might draw the air from the gable and not from the soffit, and being gable vent considered to be the worst attic ventilation source, you could have some serious problems.
> 
> Take a wood burning fireplace for instance. When you burn the fireplace, it takes all the heat from the room out. If you crank a near by window, it will draw the cold air in, leaving the hot air in the room.:thumbsup:


Greg, that seems logical, except I have looked for conformation and can't find any literature to back it up.

Have anything for us??


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## dennis (Nov 17, 2004)

> Take a wood burning fireplace for instance. When you burn the fireplace, it takes all the heat from the room out. If you crank a near by window, it will draw the cold air in, leaving the hot air in the room


Hi Greg,

Not a very good analogy, but;

The way you are thinking about it, that fireplace is heat gain in the attic with a small roof vent, and no other vents. 
A very warm room(attic) until you open the window(intake). 

To make that analogy more meaningful.
Cut short vents all along the exterior wall at the baseboard to simulate soffit vents. Enough to compensate for the draft of the fireplace. Now open the window.


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## greg24k (May 19, 2007)

It is very simple... the outside air enters your attic space at the bottom edge of your roof and is being exhausted at the highest point of your attic. This makes ventilating systems use wind and thermal convection to always move and exchange air in the attic with outside air. When you have a windy day, wind blowing across the top of ridge vent and creates a vacuum which pulls the air out of the attic. On the days when there is no wind, hot air builds up in the attic, and leaves through the ridge or roof vent which always located at the top of roof and that is why Ridge and Soffit vent system is the most efficient ventilating system.


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## dennis (Nov 17, 2004)

> that is why Ridge and Soffit vent system is the most efficient ventilating system.


I agree, unless , 
a. your ridge vent is plugged by debris or wind driven snow ( I have pictures)
b. your ridge vent is covered in snow for long periods( I have pictures)
c. your roof is made up of hips and valleys with no room for ridge vents

I am not against using ridge vents. Just trying to clear up the "short circuit " myth.


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## oldfrt (Oct 10, 2007)

dennis said:


> I am not against using ridge vents. Just trying to clear up the "short circuit " myth.



From all the reading I've been doing,
it seems more fact ,than myth.
Your demonstration just shows what 
dry smoke will do.The whole purpose 
of ventilation is to remove any moisture.

One day after finishing a reroof where the HO
insisted on keeping his gable end vents,he 
called to say something wasn't right.
When I arrived I noticed a mist in the 
attic space.It was because the ridge vent was now
drawing outside fog in through the gable vents.
We closed the vents off,he never had a problem again.

Here's something I found on damage done by
short circuiting.Although part of the problem was
the lack of adequate soffit vents,the gable end
vents greatly added to the damage:
http://www.ronhungarter.com/ventilation_repairs.html


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## greg24k (May 19, 2007)

dennis said:


> I agree, unless ,
> a. your ridge vent is plugged by debris or wind driven snow ( I have pictures)
> b. your ridge vent is covered in snow for long periods( I have pictures)
> c. your roof is made up of hips and valleys with no room for ridge vents
> ...


When the roof made up of hips and valleys with no room for ridge vents, then you use roof vents which are installed 24" from the ridge and they work just as good and efficient...each plastic vent provides net free vent area of 50-55 sq inches of ventilation.


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## dennis (Nov 17, 2004)

oldfrt,


> From all the reading I've been doing,
> it seems more fact ,than myth.


Where are these facts. I have not found any, and I don't think you can either.



> Your demonstration just shows what
> dry smoke will do.


The demonstration shows what air will do. The air that carries the moisture.



> The whole purpose
> of ventilation is to remove any moisture.


And another purpose is to remove excess heat.



> When I arrived I noticed a mist in the
> attic space.It was because the ridge vent was now
> drawing outside fog in through the gable vents.


There was no fog being drawn in from the soffit vents after you closed the gables? Either the fog started above the roof line, or the soffit vents had special filters to filter out the the humidity.

The last time it was foggy around here it was not windy ( so no wind driven low pressure pulling air out the ridge vent and from the gable vent). Was it a windy, foggy day?
And for stack effect we need a disparity between indoor and exterior temperatures. Was the attic hot enough to create enough stack effect only where the ridge vent was, and pulling the outside air in through the gable vent?



> Here's something I found on damage done by
> short circuiting.Although part of the problem was
> the lack of adequate soffit vents,the gable end
> vents greatly added to the damage:
> http://www.ronhungarter.com/ventilation_repairs.html


*Part *of the problem was lack of adequate soffit vents?!?!? There were *no* soffit vents. That was a 50's style ranch house which probably had minimal insulation and no vapor barrier.


Greg,


> When the roof made up of hips and valleys with no room for ridge vents, then you use roof vents which are installed 24" from the ridge and they work just as good and efficient...each plastic vent provides net free vent area of 50-55 sq inches of ventilation.


A good solution for a hip roof. I have a job this spring where I will be using those. They haven't been around too long.


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## dennis (Nov 17, 2004)

Okay, sorry if that was a little sarcastic.

So, two things to think about.

a. On a non windy day, stack effect will cause hot air to rise and exit out of any upper hole in the roof.

b. On a windy day, the wind does not blow just over the ridge vent. It blows against the sides of the house where the soffits are, and where the gable vents are.


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## jmiller (May 14, 2010)

If we're going to advise on building science should we not at least take the time to do a proper smoke test? On a real house, in different areas of the country?

Should the smoke go along with what you're saying, we've proved that on a gable roof it can go either way. Problem is, I can't remember the last time we roofed a simple gable, and the ventilation of mcmansions is a whole other problem. There is usually at least one short circuit built into the attic spaces or a poorly placed turtle/ridge vent. 

Let's just say you're right for now though dennis, and that the gable is extra exhaust and not a short circuit. It clearly states on the ridge vent install instructions to make sure there is AT LEAST as much intake at the eaves as exhaust at the ridge. Otherwise, you're just pulling conditioned air out of the living space to feed your beloved stack effect.


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## oldfrt (Oct 10, 2007)

Dennis,
It seems that you went toe to toe
with Ed on this a few years back and
and exchanged links on this subject:
http://www.contractortalk.com/f15/seal-gable-vents-after-ridge-vent-installed-26189/

Knowing Ed's determination to weed
out fact from fiction,he doesn't seem to
be convinced yet, as apparent in his recent
post on this thread:



Ed the Roofer said:


> The ventilation manufacturers and most widely accepted ventilation studies and theories show that the gable vent air flowage would interfere, also know as Short-Circuit the current soffit to ridge ventilation flowage.
> 
> It is a recognized short-coming by mold remediation companies that by having competing types of upper air exhaust systems, the probability of mold growth is increased and is recommended to cover up the gable vents when their is a properly functioning soffit intake flowage and ridge vent exhaust flowage already in place.
> 
> Ed


I think the OP has what he needs now
to make a informed decision.


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## dennis (Nov 17, 2004)

> If we're going to advise on building science should we not at least take the time to do a proper smoke test? On a real house, in different areas of the country?


Good idea. But different areas of the country not likely to happen. The original study by Heinrichs regarding air exchange rates of ridge vent vs gable vent, which did not include ridge and gable vents installed together, was conducted on a simple one room gable structure. And of course the usual caveats applied. "Your results may vary".



> Let's just say you're right for now though dennis, and that the gable is extra exhaust and not a short circuit. It clearly states on the ridge vent install instructions to make sure there is AT LEAST as much intake at the eaves as exhaust at the ridge. Otherwise, you're just pulling conditioned air out of the living space to feed your beloved stack effect.


I'm sure you've come across some instructions that just did not fit the circumstances. And, for example, some I&W manufacturers will tell you to install the I&W over the drip edge. Just wrong.

"at least as much intake at the eaves as at the ridge" is a basic guideline. I forget who, but one of those building science guys recommended that if he had to choose between eave and ridge vents he would choose eave vents. And I agree.
In one of my videos you can see a hip roofed structure with soffit, ridge and power fan. Look closely and you can see that the soffit on the leeward side of the roof is exhausting smoke and the windward side is intake. http://www.roofingcontractorreview....lation/roof-ventilation-hip-roof-venting.html


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## seeyou (Dec 12, 2008)

dennis said:


> one of those building science guys recommended that if he had to choose between eave and ridge vents he would choose eave vents. /quote]
> 
> These things vary from region to region, but in my little slice of heaven, there are lots of 50's gable roofs with gable vents and minimal, if any, soffit venting. We've solved some attic moisture problems by adding more intake and exhaust, but by and large, most of the attic moisture problems I've encountered are due to loose, poorly installed, or non-existent kitchen/bath fan ducting or in some cases, extreme air leakage from the conditioned space.
> 
> ...


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## greg24k (May 19, 2007)

Most new home designers and home designs today are based on efficiency, Fire and smoke protection, moisture and mold protection, good and efficient ventilation, and most homes which are built today, 95% of them have Soffit and Ridge ventilation system, because it is proved to be the best designed ventilation system. 

I am certain that if Gable and Ridge ventilation system would be a better and more efficient system, everyone would still be using it....and the only things the gable vents are being used for these days, for decoration purpose to break up huge gable space in brick, stucco or siding. I looked a few videos that were posted before, and they are meaningless, not to mention they look like the movies, made a few decades ago.


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## welterweight (Nov 10, 2009)

i do not do alot of roofing but in the north east(from talking to many pro's),it seems ridge vents and proper soffits are the way to go especially for minimizing ice damns. of course the attic has to be properly insulated.
if an attic fan is used,close up the gables and make sure the soffits are producing adequate air flow. if someone has soffits and gable vents,i think closing up the vents and adding a ridge vent is the way to go. just my opinion from doing research. no reason to have both a ridge vent and an attic fan,it just makes no sense to me.


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## marcomjl (Mar 2, 2008)

enforcer said:


> have a customer who just goyot a ridge vent. Currently have soffits ,gable vents and attic fan. Should they cover the gable vents? I would think the gable vents will now disrupt air flow. Home is in north east.


Nothing wrong with the gable vents. There will still be flow. As long as the attic can maintain the same temperature as the outside air temp.

Another reason for leaving the vents is if some dumb dumb blows insulation in the attic and blocks the eaves at least there is a little flow happening.


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