Need Attice vent diagram

[William Warner]

Does anyone have a pic or diagram explaining what occurs when both ridge vents and static "pan" vents are installed on the same roof?

I could use some good diagrams to help explain how they do not increase but short circuit attic ventilation.

Thanks!

[William Warner]

Sorry...
Title should read "Attic"

[William Warner]

Never mind....

Found what I needed... HERE

[Brian A. MacNeish]

Bill:

I looked at the referred site. My comments:

1) There's a person who should get out of the office a bit.

2) She's bought and paid. Look at how many vent companies she recommended.

3) She should look at some alternate stuff like "recent" research going back to the 1950's

4) As one researcher said (may be Joe Lstiburek): You can draw all the arrows you want on paper to tell the air where to go but you can't guarantee it'll go there.

I will now quote another different source of "new" information about attic ventilation. From a 1980's paper, Attic Ventilation and Air Sealing: A Technical Review of the Issues, prepared for the NY State Energy Research Authority and NY Dept.of State:

"Some attics have no problems even when "undervented", while other attics develop problems with presumably adequate venting."

"HOUSE-TO-ATTIC AIR LEAKAGE: The moisture and, to some extent, thermal implications of house-to-attic air leakage were first noted by FB Rowley of the U. of Minnesota in the late 1940's. In the early 1960's, other Canadian and American researchers indicated that air leakage is indeed more important than vapor diffusion, but few practioners paid attention."

"The primary driving forces for transporting air --and therefore moisture--into attics are inside/outside temperature differences and building height, yet neither of these factors are taken into account in current ventilation standards."

"In fact, there is no guarantee that provide a specified area of venting openings will yield some desired level of ventilation."


Here's another opinion of the state of the field of architecture in North America regarding building science. From the front page lead article of the June 2005 issue of Energy Design Update Teaching Architects Building Science:

"In his recently published book, Water in Buildings, (Bill) Rose quotes Max Abramovitz, the architect of the United Nations headquarters in NY, who lamented in 1949, "Actually. I am very concerned that the science of building is going to disappear. I wonder if you realize how very few men are left today who are expert in building science. They are very rare and they are passed around among the large architectural offices. You have to dig them out of their holes and revive them"

My comment after teaching a couple of terms at the architectural faculty of a university:
No wonder that about 50% of lawsuits against architects today are for water leakage; If you're not taught the basics, you can't build good buildings. Design and the fine art sensibility run through most architectural schools today. Another comment from the article when talking about building science at the likes of MIT and U. of California at Berkeley, " But at both schools the curriculum has not been extended, so the number of building technology courses is still relatively small!"

[William Warner]

Valid points Brian. I did notice all those references but this site helped best explain what can occur when a potential "short circuit" situation/installation with the diagrams. I do know that in my meager experience, the "double installation" I am refering to is no better than poorly performing gable vents and result in 60+ degree temperature differences between ambient and attic temps.

[Brian A. MacNeish]

Originally Posted by wwarner

Valid points Brian. I did notice all those references but this site helped best explain what can occur when a potential "short circuit" situation/installation with the diagrams.

William: Ask around for the actual site tested research that the "representations" in the diagrams actually occur and for what percentage of the time. These diagrams are what people "believe" will happen. Many people believe that all you need in houses to stop moisture problems in walls and attics are vapour barriers but I have pictures of rotted sheathing directly behind receptacles along outer walls that had the VB in place. Who knew the problem is air leakage, air leakage, air leakage (the researchers did) ; leave out the VB, make the drywall air tight and the problem disappears !!!


I do know that in my meager experience, the "double installation" I am refering to is no better than poorly performing gable vents and result in 60+ degree temperature differences between ambient and attic temps.

And what does the 60+ degree temperature difference actually do? Positive or negative, I'd like to see the proven research with numbers.

According to the popular "theory of venting", promoted by vendors and others, you'd want this temp difference so that the passive venting systems you talk of will actually do something since they work due to warm/hot, light (relative to ambient outdoor air), buoyant air rising and leaving at the top vents, right? And the bigger the temp. difference, the better the venting will work.


From the May 1992 Journal of Light Construction article The Science of Venting By Bill Rose:
"The best protection against condensation and mildew problems in the attic is an airtight ceiling plane- one that allows no leaks from the house below."

"Most of us picture air coming through the soffits and exiting through the ridge , in about the same amounts, following the arrows we see in venting diagrams. In real attics, the airflow rarely follows the arrows." (Joe Lstiburek must be quoting Bill Rose)

"Unless a ridge vent is designed just right, the air can blow in one side and right out the other, not helping with ventilation."

"Our research shows that wind, not thermal buoyancy, is the driving force for air exchange between the attic and outdoors. Thetmal buoyancy may play a role in air movement form the indoor space to the attic, especially in tall buildings, but its role in diluting attic air with outdoor air is negligible."

You should read some of my other posts in the threads about "inadequate attic ventilation" and "shingle disintegration"

[William Warner]

Originally Posted by Brian A. MacNeish

And what does the 60+ degree temperature difference actually do? Positive or negative, I'd like to see the proven research with numbers.

Are you saying prolonged elevated temperatures will have no effect on plywood sheathing and composition shingles? Proven research with numbers? Umm... I think the simple physics and chemistry of cumbustion is proof enough, but then again I've been wrong before. If you're trying to claim heat has nothing to do with roof deterioration, then why are there minimum clearance guidelines for combustibles near chimneys, flues, and other HEAT sources? Degradation of roof coverings is little more than slow combustion.

If you're making an argument for "air tight" and conditioned space construction then that is one point. Retro-fitting an older structure for complete air tightness is economically out of the question if not impossible. I think you are comparing apples to oranges here. As far as claiming the proven science of physics is bunk, well... I won't voluntarily follow you down that road.

[Brian A. MacNeish]

Originally Posted by wwarner

Are you saying prolonged elevated temperatures will have no effect on plywood sheathing and composition shingles? Proven research with numbers? Umm... I think the simple physics and chemistry of cumbustion is proof enough, but then again I've been wrong before.

Just what are physics and chemistry of combustion? From a reference manual: "The decomposition of wood by heat is called prolysis. As the temperature begins to rise above the boiling point of water, the chemical structure of the wood begins to break down and hydrocarbons begin to decompose." No where have I ever seen or heard that the temps of roofing materials, sheathing and attics get over 150-160 Deg.

The hottest temps are at the shingle surface where the sun's rays turn to heat. An August 2002 study on dark (the hottest) shingles in Jacksonville, Florida, found that the average temp was only 0.2 deg cooler in vented roofs versus unvented roofs. Roof venting has very little to do with shingle life when compared against quality, colour, latitude, and orientation. I have seen roofs where the north and south facing slopes were both well vented but the south facing was ready for replacement 5-6 years before the north facing. Why didn't the venting save the south slope?

If you're trying to claim heat has nothing to do with roof deterioration, then why are there minimum clearance guidelines for combustibles near chimneys, flues, and other HEAT sources? Degradation of roof coverings is little more than slow combustion.
Combustion of wood occurs in the 920-1225 deg F range. We are not even close to those temps. Degradation of shingles is no combustion process; it's simply as I said- degadation. The clearances you mention are to prevent pyrolysis of wood over the long term since the temps of flue gases can range from 300-600 deg in the normal operation of most combustion appliances, 600-900+ deg in abnormal operation and up to 2000 deg in a wood creosote chimney fire. Then you don't want combustibles touching the chimney.


If you're making an argument for "air tight" and conditioned space construction then that is one point. Retro-fitting an older structure for complete air tightness is economically out of the question if not impossible.
I know that, I ran an insulation/airsealing company for 10 years and still do a bit for friends now. It is very possible and economical to get the largest air leaks in an attic, reduce the amount of heat and moisture flow to the attic so that additional or code venting is not necessary.


I think you are comparing apples to oranges here. As far as claiming the proven science of physics is bunk, well... I won't voluntarily follow you down that road.

I am a scientist firstly and math, physics, chemistry, biology were my chosen courses. Note that I quote "studies" by building scientists and engineers. Don't know where you get the idea that I am creating new laws of physics.......just quoting new information that people whose information is from the street level have a hard time assimilating due to being stuck in time. Remember the world's largest church only apologized to Galileo in 1992 after he claimed about 1600-1610, that the earth went around the sun, not the other way as the church believed.

[ldapkus]

www.airvent.com

[Brian A. MacNeish]

Originally Posted by ldapkus

www.airvent.com

These are the last people to take the information from. If they don't sell vents, they have nothing else to sell. "Put some (or a lot of) our vents in and feel good abouit your attic/house. "Sounds like a drug dealer: "Here have some of my stuff, man! Makes you feel good!"

They certainly would not want to hear the likes of "Airseal your attic to save energy and ........prevent major moisture problems in the attic."

There was a timeI used to see small 1" vents installed in clapboard at each vertical cavity to release the moisture from air leakage and damp houses/basements that caused paint blistering with some actual water filled blisters. Now you don't see these being installed since there's been a switch from oil/alkyd based paints to latex that allows moisture to diffuse outward and not get trapped by the paint. We also have the knowledge to reduce the problem moisture sources/transmission/etc.

How much have things changed? I usually say this in my training seminars:
"In Great Grampy's time, he'd have to go to the bathroom outdoors but he could smoke indoors. Today, he'd go to the bathroom indoors but has to smoke outdoors."

Another about obtaining all your knowlwdge at the street level. I ask this question:
"If all your sex education, like most of your building education, came from the street, how many would be here now?"

See the last paragraph in this study from Las Vegas where it can get quite hot for long periods: http://www.eere.energy.gov/buildings...s/db/30974.pdf

[Roy D. Cooke, Sr]

Thanks for all the questions and answers .
I have been a believer in unvented attics for some time.
I appreciate all the questions and answers and I am sure many more are now have ideas on this subject.
Her are some web sites that also add more thoughts .
http://www.google.ca/search?hl=en&q=...ood+thing&meta=

... Cookie

[Ed Fako]

Finally, (I am still beating my dead horse.)

By the way, I just brought this topic to the front, since I felt the report I linked was well worth viewing and saving. Ed

I have been searching for this report for eons.

Does temperature difference accelerate the aging process of composition asphalt shingles.

See page 12 of this study.

http://www.fsec.ucf.edu/en/publicati...CR-1496-05.pdf

I recommend saving this report, since the end of it, in the appendixes, has full articles of quite a few other significant pros and cons on ventilation facts and theory.

Ed