Shingle disintegration question

Hi, all. Just looked at a house with 11 year old IKO RenaissanceXL organic fiber asphalt shingles that were absolutely disintegrated. Single layer of shingles over 30lb paper on a moderately sloped roof. There appeared to be sufficient venting (2 thermostatically controlled power vents, gable vents, ridge vents and 30 6"x9" soffit vents) The attic floor was R-30 fiberglass with paper down, 2X6 rafters had R-11 fiberglass. Checks indicated no blockage of soffit vents and a 2" airspace between the underside of the roof deck (1"x10" boards) and insulation. IMHO, everything looked good except the shingles. I agree with the owner that the shingles are defective. Please, any input would be greatly appreciated.




Excessive heat due to rafter insulation.

I would agree with Joe, except I wonder how shingles over unventilated cathedral ceilings hold up. Do they usually fail early?

Jim King

Yes, the rafters were insulated, however there was a good two inches of space between the insulation and the underside of the roof deck, as well as what I think was adequate soffit and ridge venting, as well as the power vents. I could feel air movement when I pulled back the insulation.

This is not an excuse for the shingle disintegration, but a clue as to the proper dynamics of exhaust ventilation.

Firstly, by having more than one type of exhaust syetem in place; ie; Ridge Vent, 2 Power Attic Ventilators and the Gable Wall Exhaust Vents, the entire air flowage has been “short-circuited.”

Think of it this way. When one of the power attic ventilators kicks on, where does it achieve its air supply from?

The path of least resistance, should be concluded.

Therefore, since the air flowage is being short-circuited in multiple manners and locations, the under soffit fresh air intake vents are never supplying any, or at least minimally, the amount of fresh unheated and non-moisture from interior humidity levels, laden air into the attic.

That, most likely would be the shingle manufacturers claim to reduce liability.

Secondly, on the rafter insulation, you stated that there was a minimum of a 2" space for air flowage and that it was unblocked. Was this due to them placing insulation baffle vents in place continuously on the top side of the insulation? Or, is this due to you observing an approximate 2" sag bowing downward in the center of the insulation between each rafter? Even if there were a 2" sag bowing downward, can you be absolutely sure that the sag is 100 % continuous, from each soffit vent all of the way up to the continuous ridge vent?

Thirdly, are there soffit vents in EVERY single rafter bay? Even if there are a substantial number of them in place, they must provide fresh air intake ventilation for every single individual rafter bay to achieve ventilation for that portion of the attic and that individual rafter bay pathway.

Now, I have never, ever been a proponent of the IKO brand of shingles. From a former IKO Representative, who now heads an ABC Roofing Supply division, I was informed around the early 1990’s, that IKO was flooding the US market with inferior quality product at a bargain basement price, just to achieve a recognizable presence.

That is just hear-say, but I have seen many instances of poor quality IKO product failures compared to most other brands being sold at that time period. Globe was another brand at that same time period who allowed their product to become inferior, prior to them going out of business.

If the ventilation aspects I spoke about earlier have merit, I would presume that the deck sheathing has suffered severe delamination as well. Possibly, if all of the decking was replaced at the same time as the roof shingles, it may not have been so negatively compromised and noticeable as of yet. But, there should be significant signs of humidity and/or moisture leaching into the plies of cdx sheathing at a minimum.


I’d just report it as deteriorated shingles and refer it to a licensed roofing contractor. You don’t have to determine the reason.

Ed, I agree with you, if there is proper vents installed from the soffits to the ridge then no other ventilation should be needed, that is if everything was done right. What you said is when the gable end fans turn on then the soffit to ridge vent stop working, thus increasing the hear under the roof deck.

As far as IKO goes I agree, I just did a roof with Cambridge 30 year and they felt like three tab shingles, they tor very easily.


Joe, I was thinking the same thing. Great minds think alike. :mrgreen:

But I also understand the who, what, why, where, when, thinking of everyone else,… I try to solve or come up with an explination too when I come across something not normal. Maybe just defective shingles but let a roofing contractor determine the issue, cause etc.

I think as good home inspectors we should know when a roof is over ventilated and I understand those who just want to defer things but I see no harm in understanding building systems and basing my report on those findings.

I’m not trying to discredit anyone, I just think in this case it’s clear whats going on.


All this hypothis is new to me. I’ve never heard of an attic being “over ventilated” or of “short-circuited air flowage”. Mr. Hoffmann stated that he felt flow in the gap under the sheathing. So I just think nobody knows what’s going on. It could be as simple as defective shingles.

And, in this case, there’s nothing wrong with telling the client you don’t know why they are deteriorated and defer it to a roofer.

I don’t simply defer. But I don’t waste a lot of time trying to figure out “why” either.

Actually, I say this whenever I see insulation against the sheathing: “In the attic, insulation was installed against the roof sheathing. Insulation increases the temperature of the sheathing, reduces the life of the shingles, and limits detection of leaks. Removal of all insulation against the roof sheathing is recommended.”

Actually, if you want it, my opinion would be that the insulation and trapped heat, not “over ventilation”, contributed to the issue. There. Let’s keep the debate going.

OK Joe, I didn’t mean that anyone just simply defers stuff and hope that wasn’t taken the wrong way.

As far as over ventilating a roof if I see soffit vents, a ridge vent and the gable end vents then the shingles are deteriorating quicker than they should, I would say the roof is not venting as it should.

I have seen roofs that actually will suck water in the gable end vents if there is a ridge and soffit vent.

And yes, lets keep the debate going, this is a good subject.

If there are power roof vents the only other source of intake air should be from gables or soffits and not both. Anything more disrupts the ability for air to properly circulate in the attic.

I think the code specifies a minimum amount of ventilation, based on the cubic feet of attic space. I don’t think it specifies a maximum.

Certainly water blowing inside the attic is an issue. But minus that, I fail to understand how too much ventilation is a bad thing. That seems to be what a few have implied (that too much “short circuits” everything). I don’t understand the physics of that.

By utilizing the gable end vents as an intake vent, you would be denying the entire attic cavity from being completely “washed” from the lowest point, where the fresh air intake ventilation inlets are supposed to be positioned.


Re: Code. Yes, there is a 1/300 and a 1/150 formula, which then creates code compliance, but if it is a design and functional issue, more attention deserves to be expanded upon, even if that means to defer to a ventilation “expert”, if there truly are such an animal in the roofing industry.

Most everything only gets proven after years of real world application versus theory and hypothesis. Most of the “Scientific” studies take place in model like, un-real world situations.

Google: Short circuiting attic ventilation, for a fuller understanding of this “hypothesis”.

I also agree, that the insulation on the bottom side of the decking seems to me to be the primary culprit for the "over-heating of the shingles premature decay in addition to the brand of them and in addition to the "short-circuiting of the ventilation flowage.



Recent research has shown that venting has very little to do with shingle life. The things that determine shingle life are: shingle quality, shingle colour, geographical location and shingle orientation

A recent month long study (August 2001 or 2) in Jacksonville. FL showed the surface temperature difference between vented and unvented dark (the hottest) coloured roofs was an average of .2 degrees F higher for the unvented roof. If .2 deg F makes the difference between the failure or succes of a roof, then we’re in big trouble with global warming coming.

The shingles in the picture look like severely deteriorated “Shangles”, a Certainteed product with a class action started against them. By chance, I inspected some up here in cold Canada last week that were 6 years old- some cracking and curling going on already on a north slope. Told the buyer if he got 7-10 more years out of them be real happy. Then I found the class action info last weekend and it all made sense.

Remember the first thing I mentioned about shingle life…shingle quality…appears what we have here- no quality or good research by the manufacturer.

From the Canadian Roofing Contractors Association website:
Although a recent study by Simpson, Gumpertz & Heger Inc., demonstrated that geographical location, building orientation, and roof colour have far greater influence on roof surface temperatures than the ventilation below, inadequate ventilation is often cited as the
reason for roof performance problems. (my note: everyone wants to quote the old line even in the face of opposing evidence)
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My comments: It appears the contractors don’t want to speak out about quality problems as they are fighting giants-the manufacturers. Pi–ing them off is not good practice!! One roofing researcher at U. of Illinois keeps commenting on roofing material quality. I’ve seen other shingles failing in 13-15 years.



It’s not the amount of air coming into the attic. It’s the pressure working against proper airflow when you have multiple intake locations. I’m going to read further for my own education. But I believe this to be correct.


I’m sorry but for the life of me I cannot understand why your source would believe that a poorly vented attic in blistering heat would not have a negative impact on asphalt shingles.

“Shangles” is the trademarked name Certainteed gives to ALL of their architectural design shingles.

The “Horizon” Shangle is one product I have personal knowledge regarding class action status.

The “Hallmark” Shangle would not surprise me, if it too was in the same legal bind, but I am not aware of that currently being the case.

I am quite familiar with the study regarding color and orientation you provided, and assimilate as many of both, the pros and cons on the side of the argument as I can, if for anything else, at least to expand my own knowledge of the topic, to enable a better judgement to be made for what specifications need to be made for varying conditions.


The manufacturers warranty still takes precedence, (although I am aware of at least one court case which utilized the manufacturers suggestions made via marketing materials, whereby the statements made in that material outweighed the actual written warranty verbage,), so therefor, I still defer to doing things as they are required to be done and then provide additional specifications to exceed those specifications, if I deem necessary.


P.S. Good discussion though.

P.S.S. After further reading, I would also like to comment that the manufacturers of roofing shingle products and auxilliary materials which work hand in hand, cite that over 90 % of all shingle roofs installed are not installed correctly, therefor negating the manufacturers long-term warranty. There are also statistics compiled by GAF and other sources, that the averager life span of a shingle roof is between 12 years to 15 years. If as they have stated that over 90 % of all shingle roofs are either inadequately ventilated or installed improperly, then the short duration life cycle does not surprise me in the least. This coincides with my 29 years in the roofing trade and 23 years of operating my own roofing contracting company.


**“Most of the “Scientific” studies take place in model like, un-real world situations.”
It appears that you don’t like science. If it weren’t for science, most of us would not be here now.

About 12 miles from my house is a siding manufacturing plant (pressed paper hardboard- like Masonite). It has south facing samples set up so as to be perpedicular to the hottest summer sun and harshest UV light in a marine salty environment- if that’s not a harsh test, what is??

The scientific studies that improve building science knowledge are not coming out a single place…US Army Corps of Engineers, NAHB, Building Science Corp, US Lung Association, U. of Mass., DOE, Canadian Natioanal Research Council, Canada Mortgage and Housing Corp., U of Illinois …the list goes on and on.

You all should read past copies of Energy Design Update and a few other leading edge rags. Although I don’t have a degree, 15 years ago, I beat out local engineers, architects, municipal inspectors, etc for the job of writing and enforcing the energy regs of the province I reside in now. (and I was from outside the province.) Later, 2001-2, I was hired to replace a building scientist at the local architectural faculty who was taking a 2 year leave of absence to do his Phd. (building science) at MIT. How could I do that? those mags plus a few other courses, seminars!!!

Totally untrue. Scientific studies are imperative, meaningful, but may produce varying results, dependant upon the bias of the researched results and for whom the research is being done for and financed by.

In the absence of waiting 15, 25 or 50 years to see actual results of product failure and success, assimilations must be done and conditions must be regulated, or else, scientific method would not be properly implemented.

My statement is made based on real life experiences, which may differ from yours, if you have either beein installing or inspecting roofs for the previous 29 years also. Your observations may be relative to dis-similar parameters than my own.

As oil prices escalate, I would put forth the suggestion, that some manufacturers have or are using additional “filler” in their asphalt impregnation phase of production of shingles. Product quality is a significant and key component of useful life of the product, but not only does poor ventilation jeapordize the warranty from the manufacturer, I conclude that it has an actual diminishment in the product and equally as significant, it adversely affects the structural stability of the roof deck sheathing which the shingle rely on for their adhesion and dimensional stability or nail hold down resistance.