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mama2girls 04-18-2009 03:42 PM

Ridge vents and/or fan?
I apologize if I don't know the correct terms and I'm sure this has been discussed... I've heard that people say to use only ridge vents OR a fan, but it's been suggested that we get both by a very reputable roofer (one who is premium/elite for Owens Corning). He said that other people will say not to get the fan too b/c it counteracts the vents, but that we might need it for our house since the ridge vents might not be enough and that it might not be 100% effective, but would be about 98% effective...Another roofer said the same thing and that we could turn the fan on if we want to, but maybe we could set it pretty high (like 160 degrees) and if it got really hot that the fan would kick on. One roofer said ridge vents only and another said fan only... They say our roof is a little difficult b/c there are several gables, areas that stick out and not much "peak" (I think it's called...) The house is 2700 sq ft 2 stories, so I don't know how much that is on the roof. There would be about only about 36 feet of ridgevents I think-and that's 3 different peaks... There has been an attic fan (that I guess hasn't worked for the last 6 years we've been here...didn't even know it should have been on), a couple gable vents (only in the front of the house), soffit vents and quite a few (11?) other "vents" in the roof. This obviously didn't work b/c the shingles deteriorated after 12-14 years...

We're really trying to make sure we get good shingles, but also want to make sure that they have the correct ventilation so they'll be valid for the warranty. We're looking at 30 year architectural shingles, so we'd like them to last! We're only looking at roofers that have great ratings on kudzu and premium/elite roofers for owens corning/GAF/Certainteed. Any info would be greatly appreciated!

Slyfox 04-18-2009 06:24 PM

I have used both power vents and ridge vent when there's a lot of hips in the design of the roof, thus not enough ridge area.
I would not recommend power vents only so long as there is some ridge.
I would set the power vents at the highest setting so they only kick on when absolutely needed,
except for the power vents that are on sections far away from the ridge vents, they would be set to kick on more frequently.

When looking for your roofer, get multiple estimates 'which its seems you have all ready' but also make sure you get everything in writing.
Insurance, work to be done, time frame for completion, guarantee, etc.

mama2girls 04-18-2009 10:04 PM

Vents different than fan?
I think the roofers have been talking about just one attic fan. What exactly are power vents? We had some vents (11), but all roofers had said they would cover them with plywood. I don't think they are power ones-just vents I think? Is an attic fan not enough? If you have power vents, how many do people normally have? Is it one thermostat or one for each vent?

Ed the Roofer 04-18-2009 11:12 PM

Most PAV's, (Powered Attic Ventilators, Power Fans, Powered Attic Fans, etc...), burn out the motor if there is not enough Intake Ventilation.

All ventilation requirements calculated need to be done precisely for the square footage of your personal home's attic floor square footage, from outside edge to outside edge in every dimension.

If the exact calculations are not done, how does anyone know how much Intake Ventilation and how much Exhaust Ventilation is needed?

Also, another factor that creates a need for additional Ventilation Requirements, is the slope of the roof.

A steeper sloped roof contains a significant more amount on cubic feet of air contained within. If the roof is a 7/12 or 8/12, then 10% more NFVA, (Net Free Ventilated Air flow), is required. For a 9/12 and 10/12 pitch, then 20% more is needed and an 11/12 or 12/12 needs 30% more.

Even the size, or CFM, (Cubic Feet Per Minute), of the PAV needs to be calculated for the correct square footage of your attic, otherwise it will burn out the motor or Suck the conditioned air out of the interior living quarters of your home through points of entry that are inherent in the Building Envelope of most homes ever built.

Ask whichever roofer that took the most detailed measurements, what the "Horizontal Footprint" of the attic floor space is. Report that back to us and I can offer to calculate the precise amount on both Intake and Exhaust Ventilation you require.

The Lanced or Perforated Aluminum soffit panels only provide between 5 to 9 square inches of NFVA per square foot, based on there new and clean performance capabilities. Most wind up getting the vent holes clogged with dust and cob webs and more importantly, with the attic insulation.

An interior attic inspection should have been performed to determine if your Intake Vents were open and flowing or clogged. This is critical.

Under NO circumstances, should you have a PAV in addition to any other upper roof vent systems, inclusing the small box vents, any ridge vent or upper gable wall vents. When the PAV turns on, the exterior weather, snow or rain, can also get sucked in through any of those intended Exhaust portals, which now have become Intake portals to allow the weather into the inside of the attic and cause interior leak damage.


Slyfox 04-19-2009 08:02 AM


Originally Posted by mama2girls (Post 262108)
I think the roofers have been talking about just one attic fan. What exactly are power vents? We had some vents (11), but all roofers had said they would cover them with plywood. I don't think they are power ones-just vents I think? Is an attic fan not enough? If you have power vents, how many do people normally have? Is it one thermostat or one for each vent?

There are attic fans that can be installed in the interior of the home, in the ceiling of a hall way, those suck the air of the interior of your home into the attic.

A power vent is and exhaust vent installed in the roof that sucks air out of the attic.
Each power vent you install will have it's own power source and thermostat setting.
I can't comment on rather or not you need one, two or more,
or if you need any at all because I would have to see the roof 'style' and take measurements to determine that.

I was just stating that there are circumstances in which I have used both ridge vents and power vents,
but I never used only power vents, because no matter how you set the thermostat on a power vent it will not run 100% of the time, thus there will always be some build up of heat if only power vents are installed.
Ridge vents and box vents both operate on gravitational pull, thus they are operating 100% of the time.

Ed the Roofer 04-19-2009 01:47 PM

The type of Powered Fan that gets installed in the ceiling of a house, to pump the interior air into the attic is called a "Whole House Fan."

You need plenty of Intake Ventilation for these to work correctly also, but in this case the Intake would normally be opened windows.

If there is not enough intake air sources for a Whole House Fan, then pilot lights can be extinguished from the suction.


Scuba_Dave 04-19-2009 02:09 PM

I used soffit & ridge vent
Then I added a fan to the gable vent - venting out
The fan was on a thermostat setting in the attic
If it was hot enough the gable fan would go on
It was strong enough to pull air from the soffit vents & the gable vent at the opposit eend of the attic

In addition I added a switch to manually turn the gable fan on
At nite after it cooled off I would turn on the fan for about an hour
This would cool off the attic & pull nice cool air into the attic
It was nice to be able to do this

Ed the Roofer 04-19-2009 03:11 PM

I use a Whole House Fan with opened windows to achieve the same affect.

I like that I can cool down my entire home in about 5 minutes or less.


mama2girls 04-19-2009 03:41 PM

I'm afraid I'm getting even more confused about what to do! We're not concerned about cooling the house-in fact the A/C does a good job, so we don't usually have the windows open (we're in Atlanta, GA, so the windows are mostly closed, except some in the spring and fall:) I'm mainly concerned about making sure the shingles last as long as they should. We definitely have the soffit vents (and I think they're clear), 2 gable vents (just vents, not powered) but they're both on the front of the house. The back of the house and the sides don't really have any vents... Of all the roofers who came out, not one went into the attic and I had suggested it... I'll check with some other roofers-if there are any left-or check with the one who did give the most detailed information. (I'll see if he has the "attic footprint".) Thanks for the info and I'll definitely take more:)

Slyfox 04-20-2009 07:41 AM

The measurements used to calculate the square footage of the roof,
can also be used to determine your exhaust ventilation needs.
Some ventilation companies actually provide charts showing the scenario's of doing so.

I apologize for steering the conversation off course about the power vents.

The fact of the matter is, none of us in the forum can give you a real recommendation on how many or what type of vents you need with out actually seeing your home.

I was just commenting in my own experience I have installed both ridge vents and a 'fan' - power vent when ridge vent was not capable of venting all areas of the roof.

Good Luck.

SERIOUS DIY 05-26-2009 02:31 PM

I recently was in a discussion about gable vents with ridge vents and soffit vents and went to the internet for answers and came across the "Ed and Dennis Show".
I have an engineering background and believe in the scientific studies. I have all 3 vents in my single ridge-line ranch and am trying to decide whether to close off the gable vents. The only thing I wonder about is in the winter when we get a big snowfall, the snow can completely cover my ridge vent. Will there still be enough ventilation through the snow to ventilate if I close off the gable vents?

Ed the Roofer 05-26-2009 04:34 PM

2 Attachment(s)

Originally Posted by SERIOUS DIY (Post 278764)
I recently was in a discussion about gable vents with ridge vents and soffit vents and went to the internet for answers
and came across the "Ed and Dennis Show".

ROTFLMAO :laughing:

Dennis and I have had very respectfull debates over the years and he does raise some interesting points, but in his self created studies, he did not offer his proof with blind study testing and an associated case history to see what would occur.

But, it is good for each of us to push each others knowledge a bit farther, where all concerned are the better for it.

Here are 2 job photos from 1 1/2 years ago during winter, 2007. Both have 100% continuous Intake Ventilation using the Smart Vent Shingle Over style intake ventilation system from DCI Products, Inc. They also both contain 100% continuous Ridge Exhaust Ventilation, using the Shingle Vent II from Air Vent Inc.

The bungalow roof had just received 14" of snow the evening before and the 12/12 2 story had just received 6" of fresh snow the evening before.

Notice how there are no hot spots on the attic, as evidenced by the continuous and even amount of remaining snow and mostly, please take note of how the Hot Air Exhaust being dispelled from the Ridge Vents on both structures have completely melted away the snow build up at it's exit point.

Ed the Roofer 05-26-2009 04:49 PM

2 Attachment(s)
Now, lets take a look at some neighbors homes from the same day at each location.


MJW 05-26-2009 07:38 PM

Remember Ed that some of those older houses in the sixties had no venting (sealed attic). It was made to do that, but it is still incorrect and should be updated.

Nice pics. :thumbsup:

Ed the Roofer 05-26-2009 08:27 PM

MJW, you are right and also the living habits and insulation R-Values are most likely not anywhere near the same, but the opposing neighboring photos were just added as a visual aide, for how the melting and ice formation starts to get created on an improperly ventilated roof.

The uniform and slower melting of the snow from the 2 roofs with Smart Vent and Shingle Vent II clearly demonstrate how proper balanced ventilation will ease the pain of potential ice damming occurrences.


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