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Attic Ventilation


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I am getting ready to reroof my home. I have researched attic ventilation on the internet and I am totally confused about ventilation requirements.

My home is a single story ranch with 2076 sq. feet of heated area and a two-car garage (529 sq. ft). It has 14-soffit vents (7X14 inches each), four gable vents (18X22 inches each), and three roof power vents.

My contractor suggested that I cover the power vent openings in the roof and install a ridge vent. Would this be a better method for attic ventilation than the power vents? Also, would the gable vents have an adverse effect on the ridge vent cooling?

Any suggestions would be greatly appreciated. Thank you.

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Agree 100% with AHIS. The shingle manufactures require/recommend (depending on the manufacturer) specific ventilation standards. I would recommend ridge venting and soffit venting, closing up gable vents, and removal and covering up power vents.

Proper ridge and soffit venting will provide a uniform air flow to help keep the underside of the roof cool. Other vent types can create hot spots, cause the shingles and sheathing to wear quicker than designed, and also possibly allow for mold growth or increase cooling load on the home. Ice damming is also a concern with inadequate attic ventilation.

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I'm wondering why there are such mixed systems there. Seems like the gable vents would be original and should function fine without the other vents. If there are cathedral ceilings or other obstructions in the attic then you will need soffit and ridge vents. If you are having a contractor due the roof it shouldn't be too expensive to have continuous soffit vents added. ShingleVent II is a good choice for ridge vent. Power vents are rarely a good idea. Pick one system and get rid of the rest.

Tom

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I'm gonna take a shot at being Kurt M and stir the pot. Question came from Georgia, answered by three northern state guys.

1. why four gable vents?

2. do the math for soffit vents vs unconditioned space.

3. why are the replys all recommending ridge vents?

4. do we really know about the power vents? what kind of power? cfm? switched?

5. why did the contractor want to use ridge vents and gable vents? dumb on the face of the question.

6. what type roof covering is the contractor using?

7. etc.

Seems the old system worked.

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Good point, Les. I just did a house for a guy who moved here from Texas, and he was really concerned about roof venting 'cause he'd apparently had problems with a place in Houston.

I'm not a fan of power vents in my area, but in Georgia or Texas, it might be worthwhile to lose some conditioned air in the interest of pulling a big blob of heat out of an attic.

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Originally posted by Les

Seems the old system worked.

It it aint' broke, why fix it?

Are the power vents just ugly? A lot of times these things are not operational anyway and are only venting by convection.

Ridge venting offers an even ventilation with a nice appearance. The key is to be sure there is enough unobstructed soffit ventilation to draw air from outside. You may need baffles in each rafter or truss bay to facilitate this by holding the ceiling insulation away from the bottom side of the roof deck. Without doing any calculations I would bet that you need more soffit vents and may be the reason the power vents were added in the first place. When using a ridge vent you would want to close off the gable vents to prevent short circuiting the flow of air from soffit to ridge.

Like less says though, if the old system is working, why change it now?

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We probably just confused the heck out of the gentleman from the Great State of Georgia.

Why wouldn't folks just go with a ridge vent? That's what I'd do.

I hate power vents. They break. They create pressure differentials. They're a mechanical solution to something Mother Nature will handle just fine if there's vents in the right places.

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Kurt,

Was he talking about electric power vents? You are from the Windy City and he appears to be in Sultry South. I have seen only one or two ridge vents correctly installed in the thousands of cornfield palaces in Mid-Michigan.

Venting is not a "one size fits all".

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Are there gas powered vents? Maybe coal fired?

I was trying to simplify. I didn't say one size fits all. I'm just trying to get the guy some basic info.

He's already got some soffit vents. He's already got roof vents (coal fired). He's got some gable end vents. Everyone is saying what's the problem with current venting scheme.

Ergo, why not install a ridge vent? It's better looking and it isn't going to change the existing venting in any substantive manner.

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Kurt, Kurt, Kurt,

Solar, methane, turbine, hot air, magic.

I was reading between the lines and can't quite figger out why the four gable vents, and the imbalance between soffit and power vents. I will admit a bias toward roofers that always want to install ridge vents.

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Well I live and work on these corn field palaces and have installed hundreds of ridge vents including my own. Properly I might add. With no call backs or problems. What exactly do you find wrong with others installations?

Are they not cutting the wood back or is there no soffit vents?

Oh and by the way my vents are all solar and wind powered.

Go Green.

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Whoa Chris,

This isn't personal! If you have done hundreds, then I likely have seen one or two of yours. We are talking large numbers here and I'm pretty sure you have seen many done incorrectly. I agree about the solar power and 99.9% of green building.

My opinion:

Usually the ridge vent is used out of expediency and cost. I think there is no or little consideration of the ridge orientation, pitch, free air space, etc. Frequently see decking mis-cut, trusses notched, squashed vents, fastened wrong or not at all, run end to end, etc. Right or wrong, I remain skeptical of any house component that becomes universally accepted and not necessarily correct.

Our poster should have learned quite alot from this thread likely has as much information as needed. He should post a few photos and get us going again!

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Thanks everyone for all of the input. A little clarification regarding the 4 gables with vents on my home. My home was built in 1985 with four gables and vents as part of the original design. My builder worked with the Georgia Power Company to include “Georgia Power Good Cents Programâ€

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I just checked the 2006 IRC, Roof ventilation, R806.2 Minimum Area. It appears that your calculations would satisfy the requirement in the IRC. Verify net free ventilating area.

If it has proven to work, I wouldn't change anything. No mold/moisture issues? Satisfactory shingle life?

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About one out of ten ridge vents I come across is loose at one of its ends. How come roofers don't secure those things with screws or at least ringshank nails?

The ridge vents (as you know) have locations to be nailed to the roof prior to applying the caps.

One must use at least a 2-1/2 inch roofing nail to secure the ridge to the deck. There are provisions for 8 or 10 nails every four feet or so.

Then the caps get nailed through the ridge to the deck. Figure two caps per foot with two nails each. That'd add 48 more nails every four feet that are holding down the vent. If the vent is loose, what's holding the cap on? Maybe you're finding this on re-roofs? The shingles are thick at the peak and the roofer didn't use nails long enough to get through the layers to the deck?

edit: I just realized that you may be talking about the ridge vents that don't get shingled. Do you folks still use those?

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