does it matter which soffit vent i use?

Old 07-05-18, 03:52 AM
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does it matter which soffit vent i use?

i have a 2 story garage/attic addition that i had added on to my house a few years back; at the time i just had the contractor frame it up and do the roofing and i was going to come in and do a board and batten siding. i never bothered adding soffits because it wasn't insulated.

Now that we have the available money to continue, we have started the process of connecting our original living space with the attic with the intent to turn that into additional rooms above the new garage.

I plan on finishing the soffits soon here and was wondering if a continuous soffit vent is better then say a 4" round louver
Old 07-05-18, 04:04 AM
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The main thing is the sq inches of intake which can be accomplished by either one long small vent or multiple larger vents. I would think a continuous vent would be slightly better .... but I'm a painter, not a pro when it comes to attic ventilation.
Old 07-05-18, 04:21 AM
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The continuous vent gives better ventilation across all rafters.
Old 07-05-18, 04:31 AM
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There are two key things making soffit vents work. One is installing insulation dams between the rafters to prevent insulation from sealing off the gap. The dams preserve an air pathway between the soffit and attic. The second key thing is to add vents in the attic, the higher the better. Either gable end vents, ridge vent or through the roof vents. You want cool air to enter down low at the soffit, flow up along the roof and hot air out the top.
Old 07-05-18, 05:24 AM
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Thanks for the replies, i do have a ridge vent and i do have baffles to install allow the air to pass behind the insulation. I had a feeling the continuous vent would align better with the baffles but just wanted to make sure.
Old 07-05-18, 05:44 AM
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I don't have the link but when checking a few years ago as to the NFA (net free area) of round vents the one mfg where I found that data listed theirs as 19%. You can see why that number stuck in my mind, that is pathetic. A 4" hole starts at 12 in² of area and ends up with less than 3 in². If you or anyone goes with round vents they need to find the associated NFA.

As for how much total venting in those soffits it is based upon the attic floor area at one ft² NFA for every 300 ft² of attic area. Match the same calculation for the ridge which it usually meets.

As X said, continuous is better.

In addition, air seal all penetrations between conditioned and attic.
Perfect air seal at garage ceiling, part of fire code.
Overkill on the final amount of insulation.

And anything else your inspector and permit requires.


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