Attic Ventilation - Ridge vent, Soffit vents and Gable Vents


#1

I need a little feedback on a recent addition to my webpage regarding unnecessarily closing off gable vents when installing ridge and soffit vents.

Here’s the link to the page

Roof and Attic Ventilation

There is a video at the bottom of the page. I’m not sure how to post or add it here so I’m hoping you are able to view it.

Thanks


#2

[quote=“dennis”]I need a little feedback on a recent addition to my webpage regarding unnecessarily closing off gable vents when installing ridge and soffit vents.

Here’s the link to the page

Roof and Attic Ventilation

There is a video at the bottom of the page. I’m not sure how to post or add it here so I’m hoping you are able to view it.

Thanks[/quote]

Well done Dennis, well done!!


#3

[quote=“dennis”]I need a little feedback on a recent addition to my webpage regarding unnecessarily closing off gable vents when installing ridge and soffit vents.
[/quote]

Great model and test.  I'm doing the same thing on my house right now. I added shingle vent 2 and kept the gable vents. I din't cut away the wood under  the ridge vent all the way to the end but held it back 4 feet from the end so the gable vent will have a reason to let air out. I also only cut alternate 12 inch sections of wood out so my ridge vent is working at one half capacity. I left the plywood over the rafters and just cut the middle 12 inches of each bay, this left the sheathing edges  a lot more rigid....DaveB

#4

One of the shortcomings of your test is that the smoke and combustion products of the incense is greater in volume than the air entering the system.

n-hydrocarbon+O2->xCO+yCO2+zH2O+heat

You are actually pressurizing the interior of your model, albeit a small positive pressure.

Therefore, you will see the smoke issuing from all the upper openings - not unlike a chimney.

If you want to conduct this experiment more accurately, you should run the incense outside of the model and allow the smoke to be drawn into eaves and gable vents.

Another shortcoming is that in fluid mechanics modeling, the path of the fluid must be scaled differently than the rest of the model in order to make the Reynolds number for flow similar in the small model to the full size case. This principle is called “similitude” (see http://en.wikipedia.org/wiki/Similitude for more info) and without it a scale model will not represent the operation of the full size case.

However, all of this is moot because you cannot see the true measure of the effectiveness of a ventilation system.

That measure is simply - how well does it cool the roofing material.

No matter how much air flows into and out of your attic, it’s not cooling your roof if it isn’t flowing against the roof.

This brings me to the final shortcoming of this experiment. There is no wind and therefore no pressure differential between one gable end and the other. Even imperceptible breezes create measurable pressure differences between openings on a house. Air flows from regions of high pressure to regions of lower pressure and it will follow the path of least resistance. Thus, the short circuit.

So to clear things up, gable vents and power vents will provide more airflow in terms of volume than soffit/ridge vent. The problem is that this air does not flow uniformly under the roof and therefore, can not cool the roof as well.

Air cools by convection and to have convection you have to have contact with something at a different temperature. More contact, more convection, more cooling.

If you’re looking for scientific evidence of the short circuiting look no further than the principles of fluid mechanics and thermodynamics.


#5

[quote]One of the shortcomings of your test is that the smoke and combustion products of the incense is greater in volume than the air entering the system.

n-hydrocarbon+O2->xCO+yCO2+zH2O+heat

You are actually pressurizing the interior of your model, albeit a small positive pressure.

Therefore, you will see the smoke issuing from all the upper openings - not unlike a chimney. [/quote]

Umm, Yes. This video concerns the “heatâ€Â


#6

Just because you decide to install ridge vent…

NO WAY, should you close off existing gable vents!

or any other vents for that matter!


#7

Dennis, I’m sorry for shooting down your demonstration. But fact is it does not accurately represent what happens in a real house.

You asked for feedback and unlike the other posters that gave you oohs and ahhs, I gave you an opinion based on experience and education in engineering and building sciences… and you rejected it in its entirety because I didn’t agree with you.

If nuclear submarines are the only thing worthy of modeling correctly, it’s a waste of our time modeling anything else.

Your demonstration is definitely cute, though.


#8

He did it to spite me from an arguement over a year ago. I did a ventilation test on a womans home with the gables open and never taped it when i did the smoke test. I have no problem with you dennis but really? I guess all those millions of dollars in research are wasted and you figured it out. No i did not watch it to be honest, I just cant beleive you waited this long to do this, wow man let it go.


#9

bodybagger,

Your comments made no sense and I pointed that out.

GTP,

It’s time to open your eyes and see the light.

What research???

I challenge you to find some published research regarding the “short circuit” myth.


#10

Well email me your address and i will have everything airvent has sent to you. I will even call them for you. Dennis i dont know why on earth you are trying to disprove a billion dollar industry. Was it not june of last year this all started and you finnaly got to it. You know i respect you. But to be honest im baffled? WHat is the point? You honestly think they did not spend millions on development on shingle vent II and cobra II? Like your truck somebody spent alot of time and money figuring it out. To be honest i have better things to do than argue a point that 95% of the roofing world knows. Have a good day.


#11

GTP,

The email is in the post.

You won’t find a study, demonstration, test, or research paper on the “short circuit” concept at airvent or buildingscience or anywhere else.

Why do you think I’m

?

I use Airvents shingle vent. It works. I even used an exterior baffle in the video. As you would know if you would open your eyes and see the light. “Out demons! Out I say. Take your pagan claws from poor Kevins’ eyes so he can be born again.” :smiley:

The “short circuit” myth does not hold up.

I don’t think so. Maybe you should ask around and see how many really believe that. My guess would be closer to 50%.


#12

Here is a suggestion Dennis.

For an accurate representation of the Scientific Method, determine through all of the input, what other conditions need to be modified or closed off.

Do the tests in various conditions, which can locally at least have a potential of justifiably validating your point.

On your behalf, I find very little actual documentation verifying the short-circuiting theory, but it still makes sense to me the majority of the time.

I have done things that are opposed to Air Vent’s recommendations, such as installing a Hip Vent, but only due to the fact that I felt it was a warranted remedy for a vaulted/cathedral ceiling situation that burned out the previous roof in only 8 short years.

I would do like wise if I felt your tests proved to have convincing full time merit, not just on an isolated one time test.

Ed


#13

Ed,

Good suggestion.

I have done some preliminary tests with other options etc. But have not had time to edit and show. So far, these basic tests seem to re affirm my ideas.
I have plans to build a hip roof with offset ridge lines to test also.


#14

All roofs temperatures raise because of the Son.
(pun intended)

Heat builds pressure in an enclosed area.

Hot air wants to escape and go upward.

You insure holes all around **the bottom **of your roof to insure air flows over everything and cools it.

The sun/the heat/the pressure pushes through everything upward toward All the vents With a force too!

What ever heat,pressure can not escape though all your vents will try to go through your roofing/ceiling.

Your hot air (pressurized air) wouldn’t come from a slightly lower vent.
It would come from your lowest vent.(soffit vents)

All vents on or near the ridge will be pushing out hot air/pressure with a force.

Sometimes “ridge vents” are necessary to release the pressure under everything on a roof.
Most roofs do not need that.
So when i come across a roof that doesn’t need that…I use a ventilation method that is more leak proof and keeps the structural integrity of the structure intact.
Do your own research on those methods.