Attic Ventilation Fail? Most Likely Casue?

1147 Views 7 Replies 5 Participants Last post by Gary in WA, Dec 15, 2012

edkrane

Discussion Starter · Dec 14, 2012 (Edited by Moderator)

Been in this home for 18 years of a 20 year home and have always attributed the loss of asphalt shingle sand to inferior shingles. Now that I'm facing a reroof situation I'm told that the likely cause of the shingle failure is due to inadequate attic ventilation.

I know little about construction, but I am technically minded and common sensical. Only this last summer have I actually been in the attic during the summertime, and it was definitely hot up there (over 100 degrees easy). There are 12 attic vents spaced evenly 6 ft. apart around the back side of the ridge, and within 2 ft of the ridge (of a 1550 sq ft house).

There are under eve vents all around the house, probably 20 or more. What I don't understand is why this design could be inherintly inadequate? There is no ridge vent, BTW. What the roofer says makes sense, and is corroborated by my research.

But shouldn't the under eve vents provide adequate air flow to get the hot attic air up through the attic vents? Unless this is just a builder's bad idea for ventilation, the only thing I can figure is that maybe the blown insulation in the attic is cutting airflow (I don't believe the insulation is blocking the vents themselves). Any response from the experienced is greatly appreciated. Thanks.

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Windows on Wash

· #2 · Dec 14, 2012

Is there any mold/mildew on the sheathing?

Attic temps will always be over 100 degrees in the summer.

Attic ventilation also has about 0% to do with shingle surface temperatures if the roof has any pitch to it.

Post up a picture and you will get better feedback.

About 20 years out of today's shingles is not bad despite their "Lifetime" warranty claims.

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HomeSealed

· #3 · Dec 14, 2012

Are there baffles installed where the soffit vents are? If not, they could very well be partially obstructed.... Probably not the primary cause of your problem as WoW explained, but you want those vents clear regardless.

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jagans

· #4 · Dec 14, 2012 (Edited)

Bs

Your shingles failed because builders would use yak dung and straw if they could get away with it. The whole ventilation issue was invented by the shingle manufacturers back when they went from an organic carrier mat to a fiberglass mat. A certain amount of asphalt was required to completely saturate the organic mats they were using which was basically cellulose based. when they dropped it too much the shingles would absorb moisture into the edges of the tabs. This is called clawing. When fiberglass carrier mats came along, there was a competitive war to see how cheap shingles could be made, so they kept dropping the amount of asphalt in the product, right up to the point where they would not perform. Before fiberglass mats were used shingles were rated by their weight. After fiberglass, they were rated by the number of years the manufactures speculated that they would last.

I cannot tell you how many squares of 235lb. (Per Square) Three Tab Organic shingles my Dad and I installed that performed for more than 30 years, and many were over non vented decks, mostly Cape Cods where they finished the upstairs, and stuffed fiberglass bat right up against the roof deck.

The reduction in asphalt weight, plus the oil shortage in the late 70's and early eighties, wherein the quality of Asphalt Flux went to hell because they cooked out all the light oils, resulted in massive shingle failures. Something had to be blamed, and it was Lack of ventilation. This was a Win-Win for the shingle manufacturers. They got out of warranty claims, and the ended up selling ventilated soffit, ridge cap, etc. etc. etc.

Bottom Line: Your shingles failed because they were probably cheapo 15 year fiberglass shingles to begin with.

Most all shingle manufacturers now produce a decent product, they no longer have cheapest price wars based on speculation like they did when fiberglass first appeared. Go with a 30 year minimum algae resistant product and you will be fine. Light color helps too. The reason I say 30 year is because it seems like that is where they start using a heavier glass mat, which takes more asphalt to properly coat, yada yada yada. And it is the asphalt that is the waterproofing. The more you got, well............... the longer you get. Ceteris paribus

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edkrane

Discussion Starter · #5 · Dec 14, 2012

Thank you each for your informative reply. The roof pitch is 7/12, and the shingles were failing massively by the 3rd winter (when I moved in -'93)...I was scooping handfuls of asphalt sand out of the gutter, and that has continued to this day. There is on many of the shingles a whitish glaze where the sand used to be...would that be fiberlgass? Also, the majority of the failure tends to not be at the ridge but beginning from 2/3rds to the ridge and downward. In the attic there is only 1 plywood sheet with a small amount of mildew (on the northern side of the house where there is some moss...Oregon winters).
The comment about cheap materials being made by a cheap builder is very valid. I've found many cheap-ass shortcuts over the years - some of them utterly criminal even seen from an amateur's perspective. "If I knew then...." Also, the sprayed insulation in the attic is a good 36" deep and looks as new as yesterday. **Unsure how to attach pics, sorry.

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jagans

· #6 · Dec 14, 2012

Sprayed?

Ed, What do you mean "Sprayed" Do you mean blown in fiberglass? Usually Pink? Blown in rock wool Usually white?

Yes what you probably see is the fiberglass mat. It sounds like the mat was improperly coated of the top side with asphalt, and the granules popped off due to freeze thaw, or just poor adhesion. There needs to be enough asphalt on the surface for the granules to set in, and adhere.

I think that Eric (WOW) asked you if you had any mold on the inside of your sheathing, and if you do not, you do not have a dew point problem, and therefore, you do not have a ventilation problem, in my opinion.

I would be very leery of a contractor that came out with a blatant statement like that, as it has no basis in fact. Oak Ridge National Laboratories did an extensive study on FRT plywood used to sheath roofs. To do so they attached temperature sensors to both the top and bottom side of the sheathing. They made mock ups of both vented decks and insulated decks. The difference between the vented and non vented was, as I recall 5 to 7 degrees F lower on the vented decks. Shingle color made quite a difference, up to a point, then the darker shingles, being hotter due to radiation, caused convection which pulled in cooling air faster, therefore cooling down the shingles.

Obviously you see where I am going with this, vis-a-vis venting and cooling down the roof deck. Wood is an insulator, and resists the flow of heat.

If you have never had a problem with ice damming or mold, you are fine. You did not say where you live, so we cannot comment on your particular installation vis-a-vis Ice Dams Flashing, Valley Flashing etc.

An architectural shingle would look nice at 7/12 slope, and would add a lot to the richness of your home.

I posted somewhere else what I just used, if you are interested.

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Windows on Wash

· #7 · Dec 14, 2012

jagans said:
I think that Eric (WOW) asked you if you had any mold on the inside of your sheathing, and if you do not, you do not have a dew point problem, and therefore, you do not have a ventilation problem, in my opinion.

I would be very leery of a contractor that came out with a blatant statement like that, as it has no basis in fact. Oak Ridge National Laboratories did an extensive study on FRT plywood used to sheath roofs. To do so they attached temperature sensors to both the top and bottom side of the sheathing. They made mock ups of both vented decks and insulated decks. The difference between the vented and non vented was, as I recall 5 to 7 degrees F lower on the vented decks. Shingle color made quite a difference, up to a point, then the darker shingles, being hotter due to radiation, caused convection which pulled in cooling air faster, therefore cooling down the shingles.

Right on the money James!

Your shingles failed because that is what they do if they are junk. Roofers (most of them) understand little to nothing about ventilation.

As James stated above, vented or not has little to do with peak surface temps.

Orientation, color, pitch, etc will all have much more to do with that.

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Gary in WA

· #8 · Dec 15, 2012

Ed, if your exhaust turtle (static) vents are spaced every 6' apart rather than code minimum, 3' apart for close-to 18 NFVA at the exhaust, you need more. http://www.airvent.com/homeowner/products/staticVents-roofLouvers.shtml
Depends on the intakes, but you need a balanced system. http://www.airvent.com/homeowner/products/intakeSoffit-specs.shtml 20 years ago, I was cutting little 7" x 7" holes for roof vents, measure yours. You might get 38 NFVA with the old ones, depends on the size screening.
Guessing your house of 1500 is 30' wide x 50' long, see why info is critical? And 1/2 of the 20 intakes on one 50' side = 10 ea. of 16" x 6" spaced every 5' apart; http://www.airvent.com/homeowner/products/intake-undereave.shtml Would meet minimum 1/150 per code, IRC though you have your own state code...

If using a closed roof (unvented), expect 10% less shingle life than a properly vented roof. Mildew/mold on the inside bottom of roof sheathing is a sign of more ventilation needed, if other causes are eliminated first.

Gary

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