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Old 07-18-2012, 04:11 PM   #1
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[Q]Proper Roof Venting


hi all, my house is in northeast USA. this past winter i had a new asphalt shingle roof installed.
The home is around 1900's (turn of the century) colonial Hip style roof.

I'm in the construction business, but dont deal much with roofing. Before installation I asked the contracted roofer about adding ridge vent. His reply was that on my home it was not neccessary "there was plenty ventilation".
At the time of installation i replaced the old T&G wood soffit with vented 2" T&G vinyl and alum fascia. i am confident the soffit has good ventilation,
however as the temps rise here attic ventilation is a concern.

Should i add a few roof vents, or listen to the roofer and not worry??
Temps here range from teens to near 100 F. summers are especially interesting, one day may be 90 and the next 50. LOL

TIA for any advise


this is the best photo i can get for now. mine is the white house.
you cant see much, but it gives an idea.



Last edited by MisterZ; 07-18-2012 at 10:05 PM.
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Old 07-18-2012, 06:07 PM   #2
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[Q]Proper Roof Venting


Whats the exhaust part of the equation?

Ideally it should be balanced so the NFA on the intake should roughly equal the NFA on the exhaust.

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Old 07-18-2012, 08:11 PM   #3
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[Q]Proper Roof Venting


Forgive me if i domt answer your question correctly, but currently there is no exhaust or traditional venting in the roof.
The roofer simply repaired any damaged decking, did underlayment, and shingled.
Before it was slate. There is no vented ridge cap such as cobra vent, or any visible venting to speak of.

From my understanding, the contractor was suggesting the roof vented naturally based on its construction.
Since the hips and roof cap are covered with shingles i dont see where any air can escape.
Far i know air is to be drawn in from soffit and exhausted out thru the roof.

Please correct me if im wrong. I will try to include a photo of the roof when possible.
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Old 07-18-2012, 09:35 PM   #4
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[Q]Proper Roof Venting


You can do a ridge vent, and on the hips, but the lower you go on the roof, the less they work. Any venting is better than none, but you probably will not reach equal. In the winter they also remove moisture before it can freeze on the underside of the sheathing without any, especially if there is no vapor barrier in the ceiling. Venting is primarily to prevent ice dams at the eaves.
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Old 07-18-2012, 09:53 PM   #5
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[Q]Proper Roof Venting


Quote:
Originally Posted by Duckweather View Post
In the winter they also remove moisture before it can freeze on the underside of the sheathing without any.

This is my main concern. I already have a moisture issue in other areas of the house that are being dealt with.
I do not need another problem in the attic too.

The plan was to add a few aluminum roof vents under the shingles near the peak.
Similar to the picture below. Also updated post #1 with a photo


Last edited by MisterZ; 07-18-2012 at 10:07 PM.
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Old 07-18-2012, 10:23 PM   #6
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[Q]Proper Roof Venting


Those would sure be better then what you have now which is nothing.
He had to have been blowing smoke up your buut with that stupid story about "natural venting".
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Old 07-18-2012, 11:10 PM   #7
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[Q]Proper Roof Venting


LOL, he didnt actually say "natural venting", but round-about implied it when asked about adding ridge cap vent.

all i want is to make sure im not a complete idiot for thinking there is no roof venting.
i appreciate all the replies, it looks like i'll be adding some roof vents.

any suggestion on what to use? or how many?
it is about a 26 sq roof. 50'x30' roughly 18' drip to peak.
i was thinking three or four of the ones shown above.
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Old 07-18-2012, 11:52 PM   #8
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[Q]Proper Roof Venting


Venting is about controlling moisture, not ice damns.

Ice damns are the result of unchecked heat loss. You can fix that with air sealing and insulation.

Add some of the exhaust vents you pictured and you will be fine.
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Old 07-19-2012, 08:44 PM   #9
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[Q]Proper Roof Venting


I would use a different brand of roof vent. I have removed more of the type you show, because they develop internal leaks, than I have put in
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Old 07-19-2012, 09:10 PM   #10
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[Q]Proper Roof Venting


You need 720 sq inches of ventilation (distributed between intake and exhaust) to fit the 1:300 rule. Static vents like you have pictured can provide 65 sq inches. So you should install 5 of them. More wouldn't hurt if you have the intake to support them.

Another option would be to install a ridge vent. You should have about a 20 foot ridge. At 18 inches per foot that would give you about the perfect exhaust ventilation without having those static vents.

Again make sure you have more intake than you install for exhaust. You should be able to count the soffit vents you installed and determine the sq inches of intake you have.

If the roofer used a synthetic felt under the shingles, then you have even more chance for condensation issues. Sythentic felt is classified as a vapor barrier so moisture can absolutely condense on the underside of the felt. All the synthetic mfg's require their product be installed over properly ventilated attics for this reason.

I am assuming you have sheathing boards on your roof. Likely with fairly large gaps between the boards. When you had slate you did have pretty good ventilation up there. The felt was probably all deteriorated - if there was any, and air could escape throughout the whole roof. You are right, now everything is sealed up tight and you need to provide exhaust.
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Old 07-19-2012, 09:14 PM   #11
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[Q]Proper Roof Venting


Quote:
Originally Posted by Duckweather View Post
I would use a different brand of roof vent. I have removed more of the type you show, because they develop internal leaks, than I have put in
One problem is they are installed wrong all the time. The one in the picture is installed wrong, and the OP probably got it off the mfg's website.
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Old 07-19-2012, 11:09 PM   #12
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[Q]Proper Roof Venting


Roofnron you are absolutely correct. I still have 80% plank sheathing, and the rest was replaced with osb.
I gave a list of requested materials to the roofer, such as deck armor(synthetic underlayment) and cobra ridge vent to be installed along roufhly 20' across the peak. Instead he used 30lb felt(which was fine for me) and no ridge vent.

When the supplies were delivered i noticed the products requested were not there. This is when i questioned the venting issue.
Guess he lied, huh. he did however use water and ice barrier is required by code.

The pic above was copied from a manufacturers website. I do agree that more often than not they are installed incorrectly.
Im open to any suggestiom as to what style vemtimg to use. I have considered getting the cobra vent and re-doing the shingled roof cap, but would rather go with a less evasive approach.
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Old 07-20-2012, 12:28 AM   #13
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[Q]Proper Roof Venting


Quote:
Originally Posted by Windows on Wash View Post
Venting is about controlling moisture, not ice damns.

Ice damns are the result of unchecked heat loss. You can fix that with air sealing and insulation.

Add some of the exhaust vents you pictured and you will be fine.
This is one of the very few times (I can't think of any others) that I have to disagree with Windows on.
Venting is very much about preventing ice dams too. If done properly for your house condition and the area that you live in (snow fall) venting will keep your roof deck from reaching a temperature that will allow condensation to develop on the underside of your roof deck at or close to the eaves causing ise damming.

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Old 07-20-2012, 06:06 AM   #14
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[Q]Proper Roof Venting


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Originally Posted by AndyGump View Post
This is one of the very few times (I can't think of any others) that I have to disagree with Windows on.
Venting is very much about preventing ice dams too. If done properly for your house condition and the area that you live in (snow fall) venting will keep your roof deck from reaching a temperature that will allow condensation to develop on the underside of your roof deck at or close to the eaves causing ise damming.

Andy.
Its on son.....

I agree with you as well Andy. I guess my point was that venting your roof to help remove the heat from a poorly sealed attic is a terrible solution to the problem.

Fix the heat loss first.

Ventilated attics are well proven and vetted designs but I have seen those roof systems ice dam quite readily and the issue was not as a result of improper venting. The roof was vented very well and more than the 1:150 rule in this case.

The issue was too much heat being lost and that is what drove the issue.

Use venting for what you need to vent, but air seal, insulate and stop the heat loss as much as possible and the ventilation will be that much less taxed.

At the end of the day, the ventilation should not be the dependent party to remove the lost heat to the attic. You should stop it were it is lost from.
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Old 07-20-2012, 05:15 PM   #15
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[Q]Proper Roof Venting


The issue we had in a project of 44 houses was heavy rain runoff could enter the side louvers so close to the roof and somehow leak internally We just changed them to a different brand and the problem ended.

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