# Attic Ventilation - help me understand it (lots of pics)



## Windows on Wash (Aug 30, 2011)

Theoretically you need more soffits.

What is telling you that there is an issue with the venting? Is there mold, mildew, rot?


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## Carling (Jul 20, 2012)

Windows on Wash said:


> Theoretically you need more soffits.
> 
> What is telling you that there is an issue with the venting? Is there mold, mildew, rot?



Where should I look for mold/rot? The attic seems fine, but I again I don't know what to look for.

The reason I don't think I have enough soffit vents is because if you compare a new house to this, a new house attic breathes from the entire perimeter of the roof while I only have 5 vents.

If I was to have to install more, where would I be putting them?

What about the baffles, do I need them throughout the roof or only where the soffit vents are?


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## Windows on Wash (Aug 30, 2011)

Carling said:


> Where should I look for mold/rot? The attic seems fine, but I again I don't know what to look for.
> 
> The reason I don't think I have enough soffit vents is because if you compare a new house to this, a new house attic breathes from the entire perimeter of the roof while I only have 5 vents.
> 
> ...


If the attic were not vented enough, it would be stagnate and you might see mold, mildew, buckled sheathing, etc.

Space them out equally.

Baffles are only needed where the soffits are.


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## Gary in WA (Mar 11, 2009)

Those appear to be 16" X 6" (?) with 37sq.in. NFVA, at 9NFVA per foot for soffits (1/300) they should be every 4' apart; http://www.airvent.com/homeowner/products/intakeSoffit-specs.shtml On the other hand, where is the house? Best if venting* every *rafter bay; http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1

Gary


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## Carling (Jul 20, 2012)

GBR in WA said:


> Those appear to be 16" X 6" (?) with 37sq.in. NFVA, at 9NFVA per foot for soffits (1/300) they should be every 4' apart; http://www.airvent.com/homeowner/products/intakeSoffit-specs.shtml On the other hand, where is the house? Best if venting* every *rafter bay; http://www.buildingscience.com/documents/digests/bsd-102-understanding-attic-ventilation?full_view=1
> 
> Gary



Every four feet? wow that means the attic is probably in bad shape.

I am located in Toronto, Canada.


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## Carling (Jul 20, 2012)

Windows on Wash said:


> If the attic were not vented enough, it would be stagnate and you might see mold, mildew, buckled sheathing, etc.
> 
> Space them out equally.
> 
> Baffles are only needed where the soffits are.



From the few times that I've been up there I don't recall seeing any such damage like mold/buckled sheathing, etc.


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## Carling (Jul 20, 2012)

Any more input on how many (if any) vents I need to add?


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## roofnron (Dec 7, 2011)

Bases on your attic footprint being 1371 sqft. 

For the 1/300 rule - 1371/300 *144 = 658 / 2 = 329 sqin NFA for intake. You have 5 x 37 (based on GBR's info) for a total of 185 - If you want to add more add at least 4 equally spaced where air would be drawn out of exhaust vents. It won't hurt to add more than four to get the air balanced correctly.


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## Carling (Jul 20, 2012)

I've started working on this project and I am running into multiple issues.

Because the slant of the roof is so low while I am in the attic I am having a very difficult time installing the baffles. 

Due to the roofing nails sticking out and the old insulation being right up against the plywood I can't even shove the baffles deep enough where they would pick up air from the soffits properly. 

At this point I am thinking the only way to do this properly is from the outside of the house. I plan on changing the soffits next year as it is, currently I have plywood in there. Before doing that I'd like to install the additional layer of R20 insulation that I have. Is there a point to even bother now or should I just wait until next year?


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## handy man88 (Jan 23, 2007)

Carling said:


> I've started working on this project and I am running into multiple issues.
> 
> Because the slant of the roof is so low while I am in the attic I am having a very difficult time installing the baffles.
> 
> ...



If I were you, I'd remove all those soffit vents and then insert baffles from the exterior.

HD sells baffles that are more rigid than the foam ones in your picture.

worse case, fashion some metal ducting and insert through the soffit vents.

You may also want to consider installing a ridge vent and getting rid of that whirly vent.


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## carpdad (Oct 11, 2010)

I'll stick my neck out and say it, "continuous soffit venting is for ice dam problems only".:laughing: Soffit venting is not the perfect solution, but a compromise between not being able to best insulate along the eave and trying to keep the roof deck cold.
Unless you confirmed having ice dam, and you've confirmed no mold, it is possible you are just letting in more cold air. If no ice dam, dead air space is better in winter. Roof fan for some cooling in summer. Both are easier retrofits. 
For your last question, you could lay down plywood on top of insulation and work little more easily. Winter is actually better for attic work. Rest of the seasons for outside work.
DIY new year!


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## cleveman (Dec 17, 2011)

I only put in fully vented soffits and I put a chute in every rafter bay, even when retrofitting. I've never heard about any negative effects because of this.

Get a skinny guy to install the chutes and do it while the weather is cool enough to be up there, but not too cold. It is not a pleasurable job.

When retrofitting an attic which has a soffit vent here and there, I've never learned how many you need, other than the 1/300 rule. I guess what I'm trying to say is, if you want all those chutes to flow air, it won't work if you have only a soffit vent here and there. The chutes closest to the soffit vents will hog all the air going up to the exhaust vents and this will result in hot spots.


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## Carling (Jul 20, 2012)

The time has come and I am about to start this project.

I am still getting conflicting information about running soffit air vents all around the house or not?

I have the rip out the plywood as it is right now to put up the baffles...


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## Windows on Wash (Aug 30, 2011)

There shouldn't be any contradiction. Full perimeter soffit venting is ideal and should be the goal.


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## jagans (Oct 21, 2012)

Whats to understand? The more the merrier. Fully ventilated soffits, and a _*good *_ridge vent. (Not one named after a snake) It ain't rocket science. :huh:


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## Windows on Wash (Aug 30, 2011)

jagans said:


> Whats to understand? The more the merrier. Fully ventilated soffits, and a _*good *_ridge vent. (Not one named after a snake) It ain't rocket science. :huh:


What do you have against the Cobra...


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## Dave Sal (Dec 20, 2012)

Windows on Wash said:


> What do you have against the Cobra...


When I bought my home the builder didn't bother to install any soffit vents. None. After learning more about attic venting I decided to add them myself. I also have two levels, and added fifteen soffit vents, evenly spaced, on each level, so a total of 30 vents. I made a cardboard template to help keep them straight and used a jig saw to cut the holes for the soffits. a well vented attic will keep your house cooler in summer and prevent ice dams during the winter.


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