Attic ventilation question


#1

Maybe you guy’s can help me understand this “short circuitâ€Â


#2

basicly,altough hot air rises the flow from the gable interferes w/more flow coming from below,when you have a fan it sucks in volume and takes it from the 1st available source-when the gables are closed the vents,ridge vents or fan will pull the air from the available vents which if done right are the soffits,tamko also disavows the warranty w/out proper venting-now you got me reading wrappers! :roll:


#3

Great drawings Dennis.

I’m a layman homeowner but I had to come up to speed quickly last winter when I discovered a moisture/mold/ventilation problem and had to put in emergency soffit vents mid-winter.

Your drawings seem to capture the gist of the short-circuiting, except that I don’t think the colder blue temperatures would be as uniform as you’re showing.

When you open up the gables you might have numbers closer to 85 right near those vents at the ends, but as you get towards the middle I think less of the cool gable-end air would be reaching there and your #'s would be higher in the middle.

Plus I think your soffit vents would contribute to more cooling, and lower #'s, than your drawing indicates.

So I’m guessing that you are wondering whether to use gable vents in combination w/ soffit/ridge vents, right?

All the roof ventilation companies seem to say “no” and the shingle companies want a uniform airflow under the roof which soffit/ridge systems are theoretically designed for.

I pretty much accept the “science” of their arguments but I do sometimes wonder if using both gables and soffit/ridge might not lower the overall attic temps a little more.

In fact, I was just about to make a new thread on this very topic, but instead perhaps I’ll see what happens on this one.


#4

One question, are those temperature numbers in your drawing actuals?

Was it really 85 outside and at the same time you measured 142-150 at those various spots under the roof?!!

If so, where is your house? It’ll make me feel a whole lot better about what’s going on the attic of my CT house. :mrgreen:


#5

dennis is not a homeowner (well im sure he owns a home) he is a roofer who is a one man crusade to save gable vents the world over :smiley:


#6

I agree Marshall.

DENNIS - wake up - you have posted now in three different questions but all about the gable vents. Do we really have to go over this again and again and again ?

I still think you don’t understand…

an old chinese proverb once said… “Beat a rock over and over and water still won’t come out of it” - take the word of the wise Dennis.


#7

i dont think hes asking advice…he’s telling us his opinion & beliefs


#8

OK, guys didn’t know the history here w/ Dennis.

But can I ask a related question?

Are his temperature numbers realistic? e.g. 85 outside and 142-150 inside the attic?

I was amazed at those attic temps, so I just took my house temps today found them to be: 76 outside in shade, 79 upstairs & 104 in attic… at 1:30pm on a sunny day in CT. I’m quite sure the 104 is hotter than it would’ve been in years past, and it’s still rising.

I’ve found that my new roof+venting makes the attic hotter in summer and colder in winter than my old roof did. The old one was was a cedar-shake base w/ 2 layers of asphalt on top (evidently the whole roof was quite porous to air, yet a good heat insulater). And it had NO ridge/soffit vents… only 2 gable windows on one end which I used to crack open 2-3" in summer and a 4’ fan on the opposite gable end, which I basically never turned on… didn’t really feel the need.

My new roof (incl.soffit/ridge vents) seems to have totally changed the climate for storing things up there and I’m not sure things are going to survive that I used to store in attic.

Underlying these questions are my wondering if I should open the gable=end windows (possibly also using opposite gable-end fan) for short periods of time in the summer, just to help cool it down a bit.


#9

personally,i know dennis to be very wise,and think he`s trying to understand the principles involved and why,no harm in that


#10

"I still think you don’t understand…

an old chinese proverb once said… “Beat a rock over and over and water still won’t come out of it” - take the word of the wise Dennis."

Maybe I just refuse to believe that you guy’s are a box of rocks. :smiley:

rpr,

those numbers are close but were not meant to be accurate.

Let me ask you a question. After looking at, and reading my comments about, the second illustration, do you really think that it could be a correct representation of what is happening in an attic on a hot day?


#11

As for opening the gable windows and running the fan, I think it is a good idea.

Here’s a link to some info I’m working on.

Roof Ventilation Basics

A little more there than what you will find on the other ventilation sites.


#12

AGAIN, I have to disagree with all the venting theories. and again I will tell you my set up at my house.

108 sq ft of soffit venting.
54ft x 3 inches of ridge venting.
6 sq ft each side for gable vents.

my house has ZERO icecicles
my house is cool in the summer

I have no problems with my attic ventalation.

I believe the wind blows through the one side of the gable vents and sucks the air through the soffit vents blows it out the other gable vent and out the ridgevent.

They all work together like one big happy family.

I forget who, but another roofer says take a tea kettle of boiling water up into the attic and see which way the steam goes. No matter how you vent it, the steam will just disapate in the attic air, it will not be sucked through a vent.


#13

my point is I’ve seen 3 different questions all pertaining to the same topic in 3 different areas within this website.

It’s ok and good that he is inquiring and trying to figure it out and getting others opinions and feelings - but why in three different places ?

Enough said… next !


#14

If you have eave vents, the gable vents short circuit the ridge vent. You will get effective ventilation around the gable vents but it will be localized and not give you thorough ventilation throughout your attic. The same thing happens when you put turbine vents on a house. The gable vent system can be effective if the wind direction is toward a gable vent and forces hot air out the other gable vent. If you want full ventilation choose one or the other, eave/ridge or gable vents. Personally, I’ll take eave/ridge vents every time.


#15

I don’t see the problem with using gable vents along with soffit vents.
Hot air rises, cool air drops.
If air comes in the gable vent, it will not be sucked right out the ridge vent, because it is cool. It will drop. The hottest air in the attic will always go out the ridge vent.


#16

simonkenton,

Good to see someone with a little common sense out there. :slight_smile:


#17

Regardless of what you think with your ideas, it is the manufacturer who warranties the shingles not you. Do what they want and they will warranty the product. Do what you want and they won’t. You do the math !!


#18


#19

you kill me tar monkey… where and when do you find the time to find these great pics ?but… your pic sums it up.


#20

Do you mean this warranty?

http://www.roofersreview.com/d/8792-1/GAF+Golden+Pledge+warranty+limitations.jpg