Shingle disintegration question

[Ed Fako]

Brian,

I finally dug out the response to the article you referenced earlier on regarding ventilation being less of a factor than shingle color and orientation.

The following is the response from ARMA, which also contains a link to the originally flawed computer modeling conclusions. (My Opinion)

Ed



ARMA disagrees with ventilation article
We at the Asphalt Roofing Manufacturers Association (ARMA) wish to express our opinion and provide insight regarding the article "What's the value of ventilation?" March issue, page 20.

The article's author, Carl Cash, principal with Simpson, Gumpertz & Heger Inc., Arlington, Mass., presents the results of a computer simulation of many variables to predict the life of shingles. He focuses on the mean temperature (assumed mean over a year) as directly relating to shingle performance. Mean temperature over a year takes into account night, winter and many other conditions that affect the temperature on a roof. Others have found that mean temperature does not accurately indicate rooftop temperature or product performance.

Roofing material performance is related to the highest temperature a material experiences and length of time a material is exposed at these high temperatures. Attic ventilation affects the highest temperature and length of time shingles are exposed to these high temperatures. A lack of ventilation can increase the time shingles experience the highest temperature by hours per day and increase the temperature on the roof by 6 degrees Fahrenheit to 15 degrees Fahrenheit. At peak temperatures on a roof, this range can make a significant difference. [Calculating] mean temperatures does not take into consideration these differences. Shingle performance also is related to granule adhesion, reinforcement strength, color and other factors.

Although Cash has an interesting theory, we suggest that, similar to a lot of computer modeling, his theory does not appropriately consider natural data. It, therefore, discounts an important factor—attic ventilation in the life of a roof system.

Russell K. Snyder
ARMA
Washington, D.C.

[Ed Fako]

Sorry this post is so late, but I always like to include the source link for what ever point I am attempting to make, as in the case of my previous ancient post.

http://www.professionalroofing.net/article.aspx?A_ID=72

Ed

[Brian A. MacNeish]

Ed:

Do you suppose that Mr. Snyder ever talked with Bill Rose?

In terms of reducing cooling costs, I have seen at least two references to having high attic insulation levels as being better than attic ventilation. So the ventilation must not reduce attic temps that much.

In the Q&A section of the Journal of Light Construction, (Aug/9 Bill mentions that he found air at the top of vent channels for a cathedral ceiling to be at higher temps and "about the same temperature as an unvented cavity". Also, "We've also found that a vented cathedral ceiling cavity is much hotter than an unvented full attic, other things being equal." So, are vented cathedral ceiling roofs failing more than the unvented full attic roof? They should be by Mr. Snyder's reasoning.

And " In addition, our research shows that some ridge vents are so well designed to exclude snow that air barely moves through them."

[Kenton H. Shepard, CMI]

Joe, I agree, but I like to try to solve 'em too.

If as Ed suggests the ventilation is at fault, and his theory seems like it holds some water to me anyway, a visual pattern of failure should exist. Even if the attic is not getting uniformly ventilated due to poor ventilation design, parts of it should be well ventilated and shingles above those areas should be in considerably better condition than those say, lower on the roof.

If the problem is defective shingles, the deterioration should exhibit more uniformity.

The problem could be a combination of both.