Soffit vent size?

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_Mitch_

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We recently purchased a home in the upper Midwest and I'd like to add insulation to the attic space. Currently there are 2 gable vents and a few slant back vents on the roof. I've read that it's recommended to add chutes between the rafters before adding insulation but I can't seem to find how much ventilation I need between the chute and outside. Currently the underside of the overhang isn't enclosed so the siding runs to the underside of the roof sheeting. There isn't any venting from the soffit. I can find 2" and 4" round louvers at the local big box store so do I use something like that? Also how do you choose which width chute to use?

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joecaption

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The width is determined by the spacing of your rafters.
What type roofing do you have?
There may be a better way to get far more venting if it's shingles.
Your also going to have to air seal the attic before adding insulation.
 

_Mitch_

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From what I understand part of the reason for soffit vents is to lessen contact between the insulation and the underside of the roof, is this correct? Also I plan on air sealing before adding insulation. Part of the reason I'd like to vent the soffits rather than the shingle vent is I'd like to change to a more modern look of aluminum soffit and fascia and ridge vent, but that's further down the road. For now I'm just trying to learn how to add insulation and do it right so I can get the most from my money. Thanks for the link though.
 

oldognewtrick

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The foam baffles are the item that allows for air flow from the soffit (intake area) to the upper area of the roof to exhaust. It creates a air space for air flow. The round soffit vents can be found at roofing supply stores, big box retailers or on the internet. This is only half of a vent system, intake with no exhaust will do nothing. When you install exhaust vents, block off the gable vents. They will short cycle your vent system.
 

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