I've been asked to answer a question regarding a touchie subject with some:

[Roy D. Cooke, Sr]

Originally Posted by mgratton

Below copied from: http://www.casma.ca/en/bulletin_01.shtml

*Although not usually recognized as a major design consideration, the proper ventilation of the attic area is an essential factor in gaining the maximum service life out of the building materials used in the roof assembly, in addition to improving heating and cooling costs. Overlooking this consideration may result in premature failure of the roofing system...*

Hope this helps,

Just a little out of date original published in 1992 updated in1996

Most articles I read now disagree with this idea.

No. 1
1992-02-01
Revision: 1996-10-16

.............. Cookie

[Roy D. Cooke, Sr]

An interesting article by Carson Dunlop
............ Cookie

http://www.carsondunlop.com/pdf/re-t...%20damming.pdf

[Brian A. MacNeish]

Originally Posted by bmullen1

TV aerials don't harm shingles at all. Normally it's the caustic droppings from birds sitting on the aerials that cause the problems.

And yes, I have seen many examples of shingles that were deteriorated early because of poor ventilation. One thing I insisted on when I was a contractor was that the roofer had to ventilate the attic very well, both top and bottom. I have been back to many of the houses that I built over the years and the shingles on them rarely gave out for at least twenty years while others in the same subdivisions were being replaced after ten to fifteen years.

Bill Mullen
Sarnia

Maybe you used a better shingle than the other guys. Maybe you installed better house, not roof/attic ventilation, and vented it to the exterior and not to the attic. Maybe you built tighter ceilings that did not allow that much moisture and air leakage to the attic where it may eventually have an effect on the shingles (It has been stated by some that interior attic moisture can cause shingles to fail prematurely.)

If these homes were in the same subdivisions that were built under the jurisdiction of a building code and officials, then wouldn't they all have at least "code ventilation" installed. Are you implying that you went beyond code requirements and that roofs with code ventilation fail?

See this thread: http://www.nachi.org/forum/f16/inadequate-roof-attic-ventilation-defect-19078/
Look at the last page picture in the research report URL in post #78

It is being said by more and more sources that shingle quality, shingle colour, shingle orientation/direction, latitude of installation and at the end of the list maybe ventilation, are the items that affect shingle life!

[Jeremiah Anderson]

Originally Posted by gromicko
Mold is a symptom. The disease and the house have to be looked at holistically... and that requires a home inspector. Who better?

I would expect nothing less from you Nick, and I agree with you.

I will add that in my experience many people want one stop shopping and therefore they tend to expect a mold inspector to write up remediation specifications, which of course we do not do. That is where the Industrial Hygenists have the edge of marketing themselves as one who can test for mold AND write up remediation specs AND follow the remediation project through to completion AND perform a clearance test upon completion.

Jeremiah
J.B. Anderson Inspections Inc.

[klott]

I have seen over 80 degrees difference in temps between a good ventilation job and a poor one, a good job definitely extends the life,(or should I say allows the shingles to last as long as they are designed) I don't need to depend on articles to know the difference, I know houses with both good and bad ventilation, and I have seen the difference in the condition of the shingles. The difference Nick is pointing out is like with auto mechanics, there are parts replacers and there are mechanics, the mechanic finds out what caused the failure, while the replacer does not have a clue, he just puts a new part on.

[Brian A. MacNeish]

Originally Posted by klott

I have seen over 80 degrees difference in temps between a good ventilation job and a poor one, a good job definitely extends the life,(or should I say allows the shingles to last as long as they are designed) I don't need to depend on articles to know the difference, I know houses with both good and bad ventilation, and I have seen the difference in the condition of the shingles. The difference Nick is pointing out is like with auto mechanics, there are parts replacers and there are mechanics, the mechanic finds out what caused the failure, while the replacer does not have a clue, he just puts a new part on.

What do you call a "good" ventilation job. Is it to code, which was based on incomplete knowledge from 45-50 years ago, or is it way beyond code? "Good" can mean al ot of things. Some people think American cars are "good" while others think a Toyota is "good"; can millions and millions of Toyota owners be wrong??? It's going to surpass GM as the largest vehicle maker in the next year or so.

I have directed people to a picture of a research test site where shingles are installed on the same slope with vented and unvented roof areas......very little to no difference appears in the shingles over the vented and unvented sections but a big difference shows between fiberglass and organic (paper felt) based shingles. No one seems to want to believe their eyes!! It's not the venting.

When people quote anecdotal stories on a technical subject, I firstly as a scientist have to say there are no controls (different shingles, different colours, different slopes, different orientation, different houses) or scientific rigidity!!! Show me a longterm study with shingles from the same batch installed on the same roof with a segmented/divided attic, half with code venting and half with none. Then I will really have a good look at the results.

As an example: In terms of venting of attics in cool/cold climates for moisture removal, a 10 year old study by the engineering dept at U. of Alberta found that in 4 matched pairs of houses in Edmonton (very cold) and Vancouver (quite temperate/mild), some houses with code venting had more attic moisture than houses with no venting and vice versa!!! Code venting was not the determinant for a dry attic. An observation that came out of the study (and I have seen repeated by others) was that in coastal areas, venting actually adds moisture to the attics so the wood is already storing moisture when the cooler weather occurs.....the wood has no/little "absorption" capacity and condensation must form on the interior sheathing surface.

[Doug Wall]

This is the most entertaining thread I've seen on this message board.
Keep up the good work guys, we always welcome the work. You make us look good.
Have a good week.
Doug Wall, AmIAQC, CIE
Radon & Mold Professionals
This is our best year ever, thanks in part (30%) to many home inspectors all over South Florida.
over 17,500 homes in seven years