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Community and Q&A

SIP on top of ICF

user-304075 | Posted in GBA Pro Help on

I am designing a house using 8 inch ICF foundation walls and a ten inch SIP on top of the walls. The SIPs will be 12′ high. The main weight in a SIP is in the strand board skins so I want both of these skins to be over concrete even though they sit on top of a 1.5″ thick sill plate.

My design is attached. My builder is concerned that if the slab settles different to the ICF wall there will be some imbalance of weight. To try and counter this I have made a ledge on the ICF wall for the slab to sit on.

Does anyone see potential problems or a better way to mount this SIP on this ICF?

Attachment process was not working so see picture in first answer below.

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  1. user-304075 | | #1

    Sorry picture attachment didn't work. See now.

  2. GBA Editor
    Martin Holladay | | #2

    In my opinion, it's time to talk to an engineer. I'm a little uncomfortable about the detail showing the slab sitting on a lip of your frost wall -- but with rigid foam under the slab where it bears on the lip.

  3. user-304075 | | #3

    Thanks Martin, although that hadn't been my question I understand your concern and will look into this.

  4. user-304075 | | #4


    I am now slightly confused. I did get the detail of the slab sitting on rigid foam over a lip from Mr Joseph Lstiburek at Building science and his method seems to be used in many applications of passive houses. Is you concern specifically in my application with the SIP extending over this part of the slab. Is the concern that the insulation will get crushed between the lip and the slab and allow the slab to settle?

    Please reference

  5. GBA Editor
    Martin Holladay | | #5

    Good point. I'm not an engineer, and I know my limitations, which is why I advised you to consult an engineer.

    Evidently my discomfort at your detail is unfounded.

  6. user-304075 | | #6


    Good feedback, I will have a structural engineer bless everything.

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