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Community and Q&A

Baffles and blocking at eaves (retrofit)

Jeff Classen | Posted in Energy Efficiency and Durability on

When doing a retrofit application in an attic we typically install 2 baffles for each soffit vent, and then block off below the baffle in order to prevent insulation from falling into the eaves. All other eaves are also blocked with scrap fiberglass so that insulation does not fill the eave.
I am having difficulty explaining to my installers why it is necessary to block the eaves that don’t need baffles, or in a home where there are no soffit vents. any good articles etc. to recommend?


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  1. GBA Editor
    Martin Holladay | | #1

    So I guess your question is something like, "Is there any disadvantage to filling up the soffits with cellulose?"

    One answer is, "It's a waste of cellulose."

    The other answer is, "Even cellulose can be degraded in thermal performance by windwashing, which is why the best blocking is rigid foam installed with a sealed perimeter (usually with canned spray foam), not a piece of fiberglass jammed in the space near the eaves."

  2. Jeff Classen | | #2

    getting installers to cut rigid foam board and sealing the perimeter would be very expensive, and difficult when existing insulation is going to remain in place (not opposed to it, I just have to sell it and the cost makes that difficult). I like the wind washing explanation, and I do at least use a paper faced batt rolled up and tucked into place.
    Any studies to validate how much the windwashing due to unblocked soffits effects the insulation?

  3. GBA Editor
    Martin Holladay | | #3

    I don't know of any such studies, but I imagine that the effects are relatively minor (so that it is probably hard to justify the cost of using rigid foam blocking that is sealed at the edges).

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