Does Roof Venting Really Prolong Shingle Life?

willworkforbeer

After doing some searching I'm confused. Absolutely roof venting is good etc etc. But then there are unvented attic systems, even better they claim? At least from a heating/cooling standpoint.

Does roof venting really prolong shingle life? Is there a basic formula to figure it out?

neolitic

The unvented attic must be
done in conjunction with a
whole house ventilation plan.
All of the moisture has to go somewhere.
It is amazing how much
moisture there is in a house.
Start here.....
http://www.contractortalk.com/f15/ne...-attics-33951/
http://www.contractortalk.com/f15/te...oisture-33952/
http://www.contractortalk.com/f15/fr...n-guide-33954/
http://www.contractortalk.com/f15/fo...heathing-2063/

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willworkforbeer

Thanks, some good reading. No simple answers it seems.

neolitic

Nope.
Turns out, the good guys
don't always get the bad guys
and have 'em tried, sentenced,
and locked up in 54 minutes or less.

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done4fun

the answer is very simple....."DONT HESITATE,TO VENTILATE"..it is an absolute must and are a varieity of ways to achieve ventilation...especially with a new installation.im a self proclaimed expert with my own method(spun from an existing method) to ventilate cape cod style homes and other trouble areas with no eave overhangs to speak of.i will glady share this info to anyone that asks.it is a way better method than the pastic or viynl garbage they sell you as a premade piece.always ventilate....ask the shingle manufacture and he will put to rest all the wanna be therioes you may hear around town.after all...it sometimes helps to know what a manufacture wants you to do on an install in regards to ventilation...so read up before having a roof put on....trust me..when a roof goes bad they have a long checklist you must pass in order to get a full warrantied roof.

regards,

kj

SLSTech

Done4Fun - sorry but that doesn't fly & all manufacturers (last I checked) warranty their shingles & other roofing materials for a properly done roof - ventilated or not. I agree, if in doubt on how to install a manufacturers roofing material - ask them & provide all relevant info including attic area, ventilation, pitch, etc...

As I recall there was a study done using two identical roofs on the same block - 1 ventilated & 1 done using Closed Cell foam directly under the sheathing - which resulted in the shingles max temperature being only 1.5 degrees warmer on a 90 degree or warmer day.

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B.K

I really don't know how long roof shingles would last on a good ventilated house compared to a non-ventilated one.

What i do know though, is if you do not have proper venting in your attic space, and it becomes to hot up there, your roof shingles (Assuming there asphalt) will start to curl. The heat rising out of the attic, and there being no proper ventilation will create a very hot attic space that will transfer right outside to your roof shingles.

EX: If it rains one day, your shingles will absorb and "X" amount of water. The heat coming out of your attic will find that moisture, dry your shingles up to fast and you'll shingle will start to curl from a dramatic change in moisture and heat.

To answer your question, yes proper roof venting will prolong shingle life. A formula to follow for a general rule is. An unobstructed vent area should not be less than 1/300 of the insulated ceiling area.

1/150 for a roof slope less than 1 in 6.

Vents, eave type, roof type, gable type should be distrubuted, on opposite sides of the building.

And there are a few other things also.
-Bill

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Tom Struble

well you talking about a couple of ways heat gets transferred,one is radiant like the sun shining on the shingles on the roof,which probably heat the shingles to the same temp regardless whether its a ''hot''or ''cold'' roof
and convection which would be hot air heating the roof surface,the more insulation as in sip panels the less convection will affect the shingle temp

My feeling is you vent a roof to lower moisture levels in the attic and to control convection heating of the roof surface

And from what i understand the more air sealing and insulation you have,the less venting needed

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Tom

naptown CR

This is the real reason for venting an attic. The most effective and low cost is a ridge vent and soffit vents. The more the better.

Tom Struble

usually when your talking sips your talking cathedral ceilings so no attic space to vent

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Tom

Crock

Inspector told me to have a minumum of one turtle back for every 150 sq. ft of attic space if no gable vents are used. (We have been approved though with less than that in the past.

That means a 1500 square ft. home should have 10 turtles at least or fewer if gable vents are used.

We have been installing the circular soffit vents lately in conjunction with turtles because you can install them fast with the right bit and they will cause a cross draft without ugly gable venting. Plus they look cool and you can paint over them without clogging them up.

B.K

Excuse me if this comes off as a stupid question.

But what is a "Turtle back?" I don't think i've ever heard of the term.

-Bill

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SLSTech

Half dome vent on top of the roof sheathing or one like this

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neolitic

Sometimes, "hats" he just means cut in
roof vents.
They aren't all created equally though,
best to read the # square inches of
free air space marked on them.

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Ed the Roofer

Man, I have not seen so much Mis-Information in one thread in a long time.

I don't have time to pick it all apart right now, but just will point out one or two major mistakes for now.

The one "Turtle Vent" is totally a misinformed ideology.

It is all based on Square Inches of Net Free Ventilation Area for BOTH Intake and Exhaust.

To meet the 1/150 requirement, you are being mis-informed.

One standard sized Turtle or Mushroom static Air Vent "Typically" only supplies 50 square inches of NFVA.

The requirement is ONE SQUARE FOOT of NFVA per either 150 or 300 square foot of attic floor space.

One square foot is 12" x 12" = 144 Square Inches, so you would need almost 3 Turtle/Mushroom Vents in that scenario.

How do you meet the "Minimum" code requirement of 1/300?

You either need to have a BALANCED Intake To Exhaust Ratio OR you need to have a vapor barrier on the warm, under side of the attic floor insulation, non-penetrated and sealed tight.

If neither of those are met, then the need for ventilation NFVA Increases to the 1/150 formula.

Unventilated, or also known as "Hot Roofs" have their place, but the Entire Building Envelope MUST Be sealed tight with no egress for moisture and air movement into the sealed insulated attic.

Show me a track home that is built correctly with that, which accounts for the majority of construction in the United States and then it would have a chance.

Manufacturers "LIMIT" their warranty on unventilated systems to a 10 year period of time in most instances I am aware of.

Cape cods present their own unique problems and solutions, due to a typical minimal or non-existent soffit for intake, so another method of Intake Ventilation must be used. Then, you need insulation baffle vents to allow flowage past the knee-wall into the peak of the attic area. Then a complete and continuous exhaust ventilation, including where the rear lower slop bathroom dormer is typically located, without any additional ventilation systems short-circuiting the flowage.

SLS, I don't have the Physics Paper handy right now, but the accelerated degradation of asphalt increases Exponentialy with each degree of temperature increase to the product.

One additional point with the closed and tight systems, is that more and more mold contaminants are being discovered due to contained moisture, not being ventilated correctly andI am not referring to Intake and Exhaust Vents for the roofing system, but rather the whole house ventilation mechanical design.

Ed

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Ed the Roofer

Good Grief!!!

THAT was my SHORT Response!!!!!!

Ed

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neolitic

Could have been even shorter if
anyone other than Worksforbeer
had followed the links.....

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Tom Struble

see Ed this is where i was going, ive only seen shingled ''hot roofs'' done on sip roofs that are very air and moisture tite,and i have never seen one with an attic.
In the old days we would paper the panel, install 5/4 on the flat and sheath over the 5/4,the fun part was figuring a nice intake detail at the eaves and adding ridge venting,from what i understand shingle manufactures don't require that anymore

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willworkforbeer

Thats willworkforbeer curmudgeon, worksforbeer implies that I'm working.

rbsremodeling

take it easy with the big words buddy

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