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Rigid foam ceiling question

user-1082090 | Posted in General Questions on

I’m building an ICF home in WV. I have my roof trusses on 24″ centers, 2×4 bottom chords, and 9’7″ from the floor to the bottom of the truss.

I would like to use rigid foam board for insulation and I’m wondering if it would be possible to use long screws with washers (Wind Lock) to screw through 6-8″ of foam into the truss? Cover it with an acrylic stucco and fiberglass mesh system.

If that isn’t a dumb idea, my follow up questions would be: What’s the best way to deal with the butt joints? Can I leave space between the sheets and then fill with spray foam? Just seems easier than taping. What about truss movement? Can’t I use the same techniques as I would with drywall? Should I use a metal lath instead of fiberglass? Is there just a better way to go about this?

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  1. GBA Editor
    Martin Holladay | | #1

    You are proposing an EIFS ceiling, indoors. As long as you are familiar with EIFS methods, and follow the recommendations of an EIFS manufacturer, I see no reason (other than the high cost compared to easier alternatives) why you can't have an EIFS ceiling if you want one.

    Q.."Is there just a better way to go about this?"

    A. Yes. Install a gypsum drywall ceiling and then a deep layer of cellulose on your attic floor.

  2. homedesign | | #2

    besides your proposal being expensive and fussy:
    *There is also a building code/ fire protection problem.
    *The thermal & air control layer would be interrupted by partitions
    *Foam shrinks (ask Joe Lstiburek)

    Cellulose is good
    "Cellulose Galore on the Attic Floor,
    Cellulose Galore on the Attic Floor......."

    Be sure to use energy heel trusses
    Be sure to "connect" the drywall ceiling air barrier across the tops of the interior partitions
    Think about using a different exterior wall strategy

  3. user-1082090 | | #3

    understood. bad idea. the trusses are already set so is there a way to lower my ceiling by adding on to the truss. that would give me plenty of space to pile up the cellulose. i don't need the 9"7" of ceiling. i had originally planned to install a lvl rim and i-joinst and use rafters so i could have an open space in the attic. changed my mind to trusses. i don't mind doing the extra work but don't want to compromise the trusses.

  4. wjrobinson | | #4


    I spelled this wrong forever...

    rigid: as in rigid foam...

    ridged: as in something that has a ridge

    Ridgid: as in the tool company

    Correct me further if need be!

  5. wjrobinson | | #5

    Ray, what is the span?

  6. user-1082090 | | #6

    AJ, the inside span is 30'. thanks to all of you for your input. i'm doing my best to learn and understand the difference between information and experience.

  7. wjrobinson | | #7

    Your truss supplier should be able to sketch a drop ceiling set up for you. I would use 2x4s attached to the trusses by glued and screwed 1x6 vertical webs that attach right at the truss Ws. If that breaks the span down enough, great if needed the 2x4 could be 2x6. If you have partition walls that break up the 30' then 2x6 ceiling joists could span and land on the partition walls.

    Post improvements to my plan... if anyone has such. Definitely would help to be onsite. Your best bet to me is a visit to the truss company and or an engineer.

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