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arcane 07-21-2010 02:17 PM

Atic: Adding Intake and Exhaust Vents (Maybe Ridge)
Hello. I live in the Bay Area in California and wanted to improve the attic ventilation (1400 sq. ft.). Right now, there is only one gable vent and four soffit vents near the porch at the front of the home. I know this is woefully inadequate for the home. What I'd like to do is to add some more intake and exhaust venting. It's a simple pitched roof with no hips.

Regarding the intake vents: I don't believe there is sufficient eaves to add additional ventings in those locations. Any area under the roof itself where I could potentially install some soffit vents, don't acutally lead to the attic so I don't think that is an option.

I think I have two options: shingle over vents, or dormer vets near the edge of the home. Personally, I'm leaning toward the shingle over vents as those are more aesthetically pleasing and less obtrusive. However, I'm having some trouble finding quality information regarding the best option. I think the three biggest contenders are Air Vent's Edge Vent, DCI SmartVent and Cor-A-Vent's In-Vent. The In-Vent has some numbers stating they have the best NFA. However, I'd be more interested in hearing from others have have used these products in the real world and their performance.

Regarding the exhaust vent: Originally, I was thinking about putting in a ridge vent, but was told by a few contractors that for the type of climate we experience, that it is probably overkill. So, they suggested a more economical alternative, which was to install some dormer vents, turbine vents, powered vents, etc. I was looking into the Aura Vents with Fan ( ) because their design allows a static vent to act like a turbine. And with the fan, I could still ventilate the attic on days with little or no wind. However, I'm not stuck on this brand, and would consider alternatives.

So, what would make more sense: ridge vs. active/passive vents?

And finally, if using active exhaust vents, I would like to hook it up to a thermostat. I've read that having a humidistat would also be recommended. Is this something I should also look into in my area?

Thanks for any advice and input!

xxPaulCPxx 07-21-2010 04:53 PM

You are looking to add ventilation - and this is probably a good thing - but why? What problem are you hoping to mitigate with adding attic ventilation?

arcane 07-21-2010 05:49 PM

Primarily to help extend the longevity of the shingles. Of secondary consequence to help keep the house cooler (of course we'll have proper insulation as well).

xxPaulCPxx 07-21-2010 06:50 PM

OK, how old are the current shingles - or are you looking at redoing the shingles and want them to last a long time?

The proper insulation for your area (probably R30 like my area here in So Cal) will make the most difference for room temp, so you are on the money there!

arcane 07-21-2010 06:57 PM

Regarding the insulation, we will be insulating between R-38 to R-45. It's too bad the PG&E rebate isn't greater for attic insulation.

We recently purchased the home, and the roof shingles were replaced recently... I think in 2008. I don't know why they didn't add additional venting then!

xxPaulCPxx 07-22-2010 02:12 AM

Ok, you are adding insulation - SUPER AWESOME!

Now don't screw with your roof further unless you actually NEED to. The best thing you can do is make sure you have clear vent chutes from the vents up through your insulation.

Without pictures and details of your house, it's impossible to help you beyond telling you to keep the existing vents clear while you insulate.

Heat kills roofs, as does cold when you add in condensation and ice damning. You live in San Fran, so you don't experience either extreme.

arcane 07-22-2010 10:49 AM

Yes, we will make sure that there are baffles through the existing intake vents.

If heat kills roofs, then wouldn't it be prudent for me to add ventilation? Considering that the only intake vents are those four soffit vents in the front, and the only exhaust is the gable vent. Are these sufficient for the roof?

I can definitely take pictures, but what further details about the home would be helpful?


xxPaulCPxx 07-22-2010 12:58 PM

Heat kills roofs... in Palm Desert. You have to be north of 150 degrees for that to happen.

FrankL 07-22-2010 04:40 PM

What about solar panel attic fans? I would assume you at least get a 30% tax deduction and they cost about $250 to 400. Does it really get that hot in SF in the summer? I know up in places like Napa during the day it can.

Frank Lardino

Yoyizit 07-22-2010 06:20 PM

"When attics with asphalt-shingled roofs are left unvented, the operating temperature of the shingles increases slightly--on the order of 2%-3% of absolute temperature. This means that a black asphalt shingle roof that is typically at 150F will be at 153F-155F. That 3F-5F increase can be important, since it translates into an approximate 15% reduction in the useful service life of the shingle. On a 15-year shingle roof, that means you may lose 2 to 3 years in service life."

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