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Old 07-19-2012, 11:30 PM   #1
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Attic Ventilation - help me understand it (lots of pics)


Having spoken to a few different roofers in regards to my conundrum I’ve decided to turn to this forum with as much information about my house as I can provide to get a basic understanding of what it is that I need to do.

Background info: my bungalow was built in 1971 and one issue I’ve come across is the lack of insulation in the attic. I’ve been talking to my neighbor and his house is generally 2 degrees Celsius cooler than my house in the summer. He has R40 throughout.

I checked my attic and I have R20 all around, which probably explains the difference in temp. I went out and bought R20 insulation batts that I want to put in. I watched a few vids on youtube about correctly insulating your attic and I’ve come across some grey areas.

Issue 1: I don’t have soffits, I have plywood under the overhang of the roof and 5 vents. Are 5 vents sufficient to get air into the attic? Do I need to cut out more, what is the general rule of thumb here?

Issue 2:
My attic doesn’t have any rafter baffles with the current insulation. Because the roof is very low it’s hard to get to the ends to check if the current insulation is blocking the air from coming. My issue lies in whether or not I need to install baffles if I am adding another layer of R20 insulation and if so should I be putting baffles throughout the entire roof or only where my vents are at the overhang.

The roof is 1,371 sq. ft.

This is what I don’t have:





Enough talk, here are the pics to give you an idea of the house/roof/attic/vents.

House:












The attic:






Opening to get into other part of roof (not sure if this is normal, I can barely fit through):




The roof vents/overhang vents:






I have only 5 of these vents under the overhang.


This is where they are placed throughout the roof:


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Last edited by Carling; 07-19-2012 at 11:37 PM.
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Old 07-20-2012, 06:58 AM   #2
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Attic Ventilation - help me understand it (lots of pics)


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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Old 07-20-2012, 08:18 AM   #3
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Attic Ventilation - help me understand it (lots of pics)


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Originally Posted by Windows on Wash View Post
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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Old 07-20-2012, 03:37 PM   #4
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Attic Ventilation - help me understand it (lots of pics)


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Originally Posted by Carling View Post
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?
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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Old 07-21-2012, 01:12 AM   #5
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Attic Ventilation - help me understand it (lots of pics)


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/pro...it-specs.shtml On the other hand, where is the house? Best if venting every rafter bay; http://www.buildingscience.com/docum...on?full_view=1

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Old 07-26-2012, 11:45 PM   #6
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Originally Posted by GBR in WA View Post
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/pro...it-specs.shtml On the other hand, where is the house? Best if venting every rafter bay; http://www.buildingscience.com/docum...on?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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Old 07-26-2012, 11:46 PM   #7
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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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Old 07-30-2012, 09:20 PM   #8
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Any more input on how many (if any) vents I need to add?
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Old 07-30-2012, 11:03 PM   #9
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Attic Ventilation - help me understand it (lots of pics)


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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Old 12-28-2012, 01:25 PM   #10
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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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Old 12-29-2012, 11:27 AM   #11
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Attic Ventilation - help me understand it (lots of pics)


Quote:
Originally Posted by Carling View Post
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?

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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Old 01-01-2013, 02:17 PM   #12
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Attic Ventilation - help me understand it (lots of pics)


I'll stick my neck out and say it, "continuous soffit venting is for ice dam problems only". 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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Old 01-01-2013, 08:09 PM   #13
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Attic Ventilation - help me understand it (lots of pics)


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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Old 04-12-2013, 11:34 AM   #14
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Attic Ventilation - help me understand it (lots of pics)


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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Old 04-12-2013, 11:40 AM   #15
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Attic Ventilation - help me understand it (lots of pics)


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

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