What height to place attic vents?

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Old 06-14-14, 10:15 AM
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What height to place attic vents?

Hi

My house only has one high vent in the attic and it's probably at the mid way point in height of the box gable roof. This video says to place attentional vents at the same height as the last. But my vent seems too low compared to all the other vents i see (my house is old 1950s). It appears convention has moved on to placing the vents at the highest point possible.

So it seems i have two options, either place the vent in line with my current vent

or place one vent directly above it.

Or place two vents above it to either side.

Any thoughts?

thanks
oman
 
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Last edited by oman4eva; 06-14-14 at 11:07 AM. Reason: added photo
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Old 06-14-14, 10:51 AM
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Years ago attic venting was almost an afterthought. Today we understand more about moisture and heat flow.

The old, but still followed, guideline is 1 ft˛ of net free vent area (NFA) for every 150 ft˛ of attic floor. That number is then divided half high and half low in either soffit, gable, roof, or ridge vents. Half of that number is considered sufficient IF the ceiling plane is air tight and has a good vapor barrier.

Check the size (NFA) of all vents you have to see how far away from the guidelines you are. I suspect the correct choice would be to add more venting above the current vents. Maximizing the height difference between high and low maximizes the pressure difference and give you the most air flow. Leaving the one in the middle will do no harm.

Bud
 
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Old 06-14-14, 11:10 AM
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Thanks Bud,

I did the calculations on the NFA and i only need one more vent, but given the one i have is at the 50% height perhaps i'll get two more and spread them equidistant on either side of the current one, around 1 ft down from the peak of my roof.

cheer
oman
 
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Old 06-14-14, 02:30 PM
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I'd be installing a ridge instead.
Vents the whole roof all the way to peak and every rafter bay.
Looks a whole lot better, no holes have to be cut on the roof.
 
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Old 06-16-14, 05:28 PM
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Hi Guys,

I put up the vents on the weekend, I did have one question. I placed the vents so that the hole was as big as the intake of the vent, and allowed about 1" of overlap of the shingles on the vent. However as i was doing this it looked like the shingles were too close to the outlet of the vent and hence blocking the air flow (defeating the purpose of the vent). I did watch a video and they suggested the 1" overlap so i left it as is.

I wondered what people thought about the overlap of the shingles? Is 1" too much given they're so close to the outlet of the vent? I'm very tempted to cut the shingles back a little to give more space for air flow.

Thoughts?

cheers
oman
 
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Last edited by oman4eva; 06-16-14 at 06:23 PM.
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