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Energy-Smart Details

ICCF Foundation with Open-Web Floor Trusses

The Perfect Block foundation system answers the call for a deep basement, low thresholds, and minimal concrete

When designing custom homes, we are often charged with meeting highly specific client goals, as in the case of a recent build. The homeowners wanted a 10-ft. rather than the more conventional 8-ft. basement height. They also wanted the first floor to be as close as possible to the finished-site grade. Additionally, they wanted a floor system to accommodate the bulk of the mechanical components, reducing that which would hang below the joist level. Keeping foundation concrete to a minimum was another objective.

The floor assembly consisted of a trimmable open-web floor truss hung on the inside of a Perfect Block ICCF foundation system, which is an insulated composite concrete form measuring 1 ft. wide by 1 ft. tall by 4 ft. long. The roughly 5-in. core of the block is filled with reinforcing rebar and concrete; this system uses up to 70% less concrete than a conventional foundation pour. The block is made up of recycled post-consumer/post-industrial expanded polystyrene foam (EPS) that has been run through an automated process to convert it into a lightweight aggregate in bead form. This system works well for a deeper-than-average basement because you can simply add another course of ICCF blocking.

The open-web joist floor framing—14-in. joists spaced 24 in. on center—houses most of the plumbing lines and utilities, keeping them inside the thermal envelope. While we could have had spec’d custom floor trusses, the builder appreciated the ease of working with a pre-manufactured joist with trimmable ends. Typically, such joists are sold in 2-ft. incremental lengths, which means you can get very close to the required span. The trimmable ends allow for final custom fitting. Coupled with 1-1/8-in. Advantech subfloor, the system makes for a solid floor with little deflection.

To limit the height difference between the finished grade and first-floor elevation,…

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11 Comments

  1. Kyle Bentley | | #1

    Alexandra,

    If you wouldn't mind, I've got a question or two about the ICF detail that is shown in the picture. At first glance, it seems that nearly all of the load from the exterior wall is placed outwards of the actual concrete, and is resting on the ICF component of the wall. Is that the case, and if so, is the perfect block strong enough to transfer the load by itself to the footing? Not knocking it, only trying to be more informed. I tried downloading the perfect block tech. docs to investigate some of the material properties, but it's behind a contact form.

    Thanks!

    1. Expert Member
      Malcolm Taylor | | #4

      Kyle,

      I wondered about the same thing, and also what supports the truss hangers? All the plates under the interior wall don't appear to have anything to attach to or bear on.

      I'd be interested to know what the function of the 2"x4" plates under the subfloor is too.

    2. Chris D | | #6

      Behind the contact form or not, all of the links are readily available in the HTML source for the page (Right Click > View page source) and can be downloaded. Here's the PDF ones:

      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/8in-ICCF-STEM-MAT-24-PDFS.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/8in_-Block-w_-Stem-Wall-Foundation-PDFS.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/10in-ASSYM-MonoSlab-Mat12-PDFS.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/10in-ASSYM-MonoSlab-Mat24-PDFS.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/10in-ASSYM-Structural-Details-24_-OC-PDFS.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/10in-ASYM-ICCF-STEM-PDFS.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/10in-6x6-Core-Stem-24in-MAT-PDFS.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/10in-6x6-Core-STEM-Mat12-PDFS-1.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/10in-6x6-CORE-Structural-24inMat-PDFS.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/Ledger-Details-Feb-2020-PDFS.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/PILASTER-DESIGN-Sheet-CMB-WALL-CONCRETE-COLUMNS-PILASTERS-STIFFENERS.pdf.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/Pilaster-Design-Sheet-A1-thru-A4-PDFS.zip
      https:\/\/theperfectblock.com\/wp-content\/uploads\/2020\/08\/Ledger-Details-with-Curved-Wall-PDFS.zip

    3. Alexandra_Baczek | | #7

      We worked with Simpson engineers we have a saddle hanger that comes up over the top of the mud sills beyond the foam. Also note we have a 2x4 wall that is full bearing between the footing and the bottom of the joist. our engineer had all the confidence in the detail.

      1. Expert Member
        Malcolm Taylor | | #11

        Alexandra,

        Just for clarity:
        - The strap from the hangers attaches to the top of the sill-plates. How is what looks like a 2"x3" extension to the sill-plate attached?
        - What is the function of the 2"x4" plates below the sub-floor?
        - Why is there a small block on top of the 2"x4" wall inside the foundation you describe as load-bearing.

  2. M Gillespie | | #2

    How did you thermally isolate and insulate the basement foundation/floor using the Perfect Blocks so that there are no thermal bridges?

    1. Alexandra_Baczek | | #8

      We have 2 inches of EPS between the perfect block and the face of the basement slab. Understand that the delta in temperature is very minimal in that location as well.

  3. Luke_P | | #3

    Is there information on R-value of the perfect block foundation wall (without the interior rigid and rockwool insulation)?
    Is there information on the strength of the insulating portion of the perfect block foundation wall?
    I also won't give me info to download technical data that should be openly available.

    1. Alexandra_Baczek | | #9

      We would have to defer to the manufacturer for that information. Its EPS foam which we would assume an R-4 per inch.

  4. William Hullsiek | | #5

    Logix ICF has a similar assemble, where you can install an interior corbel ledge, so the truss sits on top of 3 inches of ICF wall. Alexandra needs her own channel on the Build Show.

    1. Alexandra_Baczek | | #10

      William, we are aware of that, thank you! We like the perfect block for this project because of the environmental approach in that perfect block is 100% recycled material.

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