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Community and Q&A

How to Improve Ventilation with Short Soffits

johndoe2015 | Posted in General Questions on

My house is a 2 story colonial and the soffits are roughly 3-5 inches deep. My goal is to increase ventilation in my attic. I may eventually enclose the attic to help my A/C work more efficiently but that’s a future consideration. I recall drilling through a soffit to run a coax cable one time and it seemed like the soffit was just a 2×4 or similar piece of lumber, not vented. I currently have two gable vents and I think I have a ridge vent (need to verify). I was wondering if you have any advise on what I can do with my very short soffits that have fiberglass stuffed in them. I saw there are 1-2″ circular louvered vents available. I think a ton of 2″ holes in a 2×4 might weaken it too much so I was wondering if it would be worth putting 1.5″ louver vents. How many would I need to put in each soffit rafter bay? The attic is roughly 750-800 square feet. Any other ideas would be appreciated.

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  1. Jon_R | | #1

    > other ideas

    Consider that air sealing the attic floor might get better results for similar effort.

    1. johndoe2015 | | #2

      Thanks. I am actually in the process of air sealing the attic floor now! I just didn't want to add so much detail to my original post that it would get too long.

      I would also like to know how/if I can improve the soffit ventilation.

  2. johndoe2015 | | #3

    Does anyone have any ideas? If the 1.5" louver vent idea doesn't work should I just stuff mineral wool batts into the soffits when I re-insulate the attic?

  3. rocket190 | | #4

    Those should work for you.

    1. johndoe2015 | | #7

      How would these be installed? A slit cut through the length of the 2x4 soffits and inserted in?

      1. rocket190 | | #8

        Yes, otherwise if you can remove the 2x4 soffit without damaging the fascia trim, you could rip it down the thickness of the vent and re-install. If you had to you should be able to remove the fascia trim and board fairly easily and then do the same thing.

  4. Expert Member
    Akos | | #5

    If your gable and ridge vent is sized correctly, adding additional venting won't get you anything.

    I won't bother with soffit vents, seems like unnecessary in your case. Focus on air sealing your top plates there instead. Stuffing mineral wool batts is not air sealing, it just makes for a great filter for the air leaking out. For proper air sealing, you need to get some two part spray foam or mastic over the top plates.

    1. johndoe2015 | | #6

      Thanks I am planning to air seal soon. I wanted to add soffit vents/baffles before I reinsulated the ceiling so down the road I can remove the gable vents and make the attic a part of the building envelope to help the attic AC. Do you think air sealing the attic and beefing up the attic insulation to R60 would be more practical/good enough and just let the AC work harder?

      1. Expert Member
        Akos | | #9

        Removing the gable vents and brining the attic into the conditioned space is a whole other thing. Generally the way that is done is by removing all the insulation on the floor and spraying the roof and gable ends with closed cell foam, not a cheap or simple conversion. Plugging the gable vents and adding some batts to the rafters doesn't work, it is a quick recipe for moldy mess and rotten roof deck.

        Usually the simpler way to deal with AC in the attic is to build a small insulated and air sealed doghouse over the air handler out of rigid foam and encapsulating all your ducting and registers in spray foam. Requires much less SPF, way cheaper to do and works almost as well.

  5. Ryan_Konecny | | #10

    I’m in a similar situation. 1910 home in Chicago with essentially no soffits. We are considering using the attic space someday too, mostly just for storage. I’m looking at adding either slim soffit vents as posted above or an edge vent such as the one airvent makes.
    With aridge vent above and then furring the rafter cavities to create baffles w rigid foam and acoustic caulk. Then possibly spray foam over.

    But honestly the more I consider this the more I realize this may not be worth the small space gain in an attic. I’m leaning more towards leaving the gable vents and adding a ridge vent and leaving it outside the thermal envelope. My only issue is the house has about 3’ of sloped ceiling below the attic that I’d like to have vented somehow.

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