Walk-Out Basement Options


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I'm working on a custom home that will have a Walk-out Basement.  The wall on the front will be a 10' retaining wall and the 2 side walls will be retaining also but varying from 0 to 10'.  I will be using SIP's for the upper 2 floors.  The lower floor (Basement) will be either CMU or ICF with a stone veneer.


My questions if I use ICF are as follows:

  • What thickness would be appropriate for the 10' retaining wall?
  • How would the stone veneer be applied?
  • Should all of the lower floor walls be ICF and if so full height?
  • At the main floor level (top of wall) can I simply have a 2x6 PT plate with joists on top of the ICF?
  • Where should the upper floor SIP walls align with the ICFs? 

If instead I use CMU:

  • Would you use CMU for the entire lower floor exterior walls or would you use SIPs for the "walk-out" walls (ie: walls above grade)?
  • Assuming the retaining wall is a combination of 8" CMU with a 48" tall 12" CMU pony wall, which face would you align (inner or outer)?


Note:  In either case, I will be using an engineered retaining wall (thickness and reinforcing)

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My most recent ICF project:


1) Thickness. I had a 14'  tall ICF foundation supporting a precast plank garage floor and used a 10" core with ASTM Grade 60 deformed bars, #6@48" oc horizontally and #6@16" oc vertically within 1/3 of the tension face. I think a 10" core should suffice for your project, but of course you'll have to run calcs for the reinforcing depending on your soil class, equivalent fluid pressure, etc.

2) Stone veneer can be adhered (lick and stick), following the MVMA guidelines, with the drainage material and lath attached directly to the ICF web stiffeners:



3) You can certainly do the entire foundation in ICF. Advantages: one system; consistent construction and continuous insulation. Disadvantages: cost; designing the lintel reinforcement for any punched openings. If the upper floor is going to be framed, I would recommend framing any significant portions of the exposure.

4) Yes, you can place the sill plate for the upper floor directly on the ICF. A word of caution, however: there can be significant settling of the concrete pour within the ICF form which results in a top of wall that isn't level and requires a lot of shimming when installing the sill plate. Joists are installed "normally". An alternative is to hang the joists off a ledger that is attached with a specialty hanger such as the Simpson ICFVL; this type of solution is helpful when you need a flush entry.

5) The best solution for the upper floor walls is to use a tapered form for the ICF top course that allows you to align the sill plate with the outer edge of the ICF form, though you can also cantilever the sill plate over the form (if your local code allows). This allows you to align the SIPs however you want to best work with the exterior finishes:



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All exterior walls are FoxBlock  and very similar to Quadlock. We used Quadlock for years but Fox is a better product for us. Vertical siding is a difficult to attach unless you use horizontal purlins. BIGGEST DOWN FALL OF ICF is sunshine and no foam can be left exposed to daylight.


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