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My house has soffit vent along the eaves of the roof. I am finishing up the attic to create a home office, and I am wondering how should I treat the vents... clearly they are not going to have access to the attic, which is going to have AC.

The soffit vents are all around, like this model here:

enter image description here

We are in New England, where the winters are brutal. Ice dam formation on the roof is a real issue, and so the vents are connected to these rafter vent baffles to make the temperature of the edge of the roof uniform (if the edges heat up, the snow melts and forms ice, leading to a dam).

enter image description here

The area where the baffles are is going to be enclosed behind drywall, I do not have to remove them for aesthetic reasons. I am thinking of closing the top edge with staples, backing them with insulation, and let them do their thing in this closed space.

Any suggestions? Am I doing the right thing, or should I remove the baffles?

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  • I'm not sure what you mean by "clearly they are not going to have access to the attic". Normally soffit vents do create access to the attic. Also, what does "have AC" mean? Please revise to clarify. Does "finishing up the attic" mean that you're creating a habitable space? We really need more information. It sounds like you're planning a hot roof, which isn't advisable.
    – isherwood
    Dec 7, 2020 at 19:17
  • Yes, the intent is to create a home office in the attic, and to climate-control the space with heating and AC.
    – 0xF2
    Dec 8, 2020 at 23:34
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    I went on the roof and confirmed we have a (nicely done) ridge vent, so I will add panels from the baffles all the way to the ridge vent, connecting the gables and ridge as per @isherwood's answer. Only question remaining is if I can use foam board insulation behind them, or fiber glass is only option.
    – 0xF2
    Dec 14, 2020 at 3:28
  • Fiber glass is the way to go, as it simplifies fire code requirements (no need to fire-proof the insulation).
    – 0xF2
    Apr 3, 2021 at 1:47

2 Answers 2

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Those baffles can't "do their thing" if you close one end. You need a complete ventilation circuit between the soffit and the ridge to prevent extreme temperatures on your roof deck and heat migrating into your living space, followed by ice dams in winter.

You need to maintain ventilation against the roof sheathing the entire way up, otherwise you'll build what's known as a "hot roof". That has significant drawbacks and implications for energy efficiency and moisture management. Here's what it'll look like:

enter image description here

source

Be sure you have a good understanding of why this is important and how to accomplish it before you proceed.

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  • The attic also has a ridge vent. Boy, is there a debate on what to do with the gables on the FHB site! Thanks you for the link, lots of information there.
    – 0xF2
    Dec 12, 2020 at 5:28
  • Reading all the material, it looks like the "right" way to do it is baffles all the way to the top, a ridge vent, insulation behind the baffles, and then fire protection behind the insulation. From comments, it also looks like "success may vary" depending on what the roof shape and location are like, and that roofs not built recently still work without all this, but then some craftsman expertly designed it.
    – 0xF2
    Dec 12, 2020 at 6:00
  • One more question: assuming baffles all the way to the top, can one use foam panel insulation behind them, instead of fiberglass? I assume either insulation type will still require fire-rated panels behind them.
    – 0xF2
    Dec 12, 2020 at 6:01
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    Anything rigid enough to prevent collapse of the vent cavity is fine. Ridgid panels are a common solution. In fact I'll be doing the same thing in my garage soon.
    – isherwood
    Dec 13, 2020 at 14:25
  • asuperiorinspection.net/attic-insulation — nice resource.
    – 0xF2
    Dec 14, 2020 at 3:33
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Do not remove or close off the baffles. As you noted, they're there to allow air to flow under the surface of the roof keeping the temperature there even to prevent ice dams from forming and all the trouble they lead to.

The baffle is designed to allow you to insulate the rafter bay while still allowing for this air flow. Other than "closing the top edge with staples (I'm not sure what, exactly, that means) you're right on track.

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  • So, I should treat the space behind the drywall as a "cold space", with the baffles backed by glass fiber insulation? Or something else? The staples are because the baffle model I have is open-ended, and spills cold air into the rest of the attic.
    – 0xF2
    Dec 8, 2020 at 23:36
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    youtube.com/watch?v=58_1gb5NQ9c
    – Alaska Man
    Dec 8, 2020 at 23:44
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    You'll have a channel for air movement between the bottom of the roof deck and the top of the baffles. Under the baffle, you'll insulate. Once your insulation has been inspected, you'll drywall/tape/mud/paint to create a finished interior surface. You must allow hot/cold air to "spill" into the roof vents. If you don't have roof vents, now's the time to install 'em.
    – FreeMan
    Dec 9, 2020 at 14:56

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