This is part of our Designing with ICF: A Technical Guide for Architects & Engineers.
Direct Answer: ICF walls are structurally superior to CMU block because they are monolithic. Engineering them as "masonry" wastes money on unnecessary steel. You should design them as continuous reinforced concrete flat walls according to ACI 318.
The "Deep Beam" Lintel Strategy
The most common over-engineering mistake we see is specifying steel I-beams above garage doors or large sliders.
The Reality: The ICF wall above the opening is the beam.
If you have 24 inches or more of concrete wall above an opening, that section acts as a deep beam.
* Capacity: A 6-inch core with proper rebar tension keys can easily span 16 feet.
* The Stirrups: For long spans, we install "stirrups" (shear reinforcement) made of bent rebar to tie the top and bottom tension bars together.
Rebar Schedules: What We Actually Build regarding Spacing
Engineers often spec "weird" spacing like 15 inches o.c.
Builder Reality: ICF webs are typically spaced at 6 or 8 inches.
* Element ICF: Webs are at 6 inches on center.
* Design Tip: Specify vertical rebar spacing in multiples of 6 (12", 18", 24") to match the web layout. This ensures the bar sits perfectly in the "saddles" and doesn't get displaced during the pour.
* Standard Spec: #4 or #5 bar at 18" o.c. Vertical and Horizontal is a common, robust residential spec.
Handling Point Loads
When a heavy girder truss lands on the wall:
1. no-Pilaster: Often, the wall capacity alone (at 4,000 psi) is sufficient without thickening the wall.
2. The Pilaster: If needed, we can cut the foam out on the inside face to create a wider concrete bearing surface, or simply increase the rebar density in that 12-inch wide vertical "column" within the wall.
Concrete Mix Design for Engineers
Please do not just copy-paste your standard footing mix notes.
ICF Recommended Mix:
* Strength: 3,000 - 4,000 psi.
* Aggregate: 3/8" (Pea stone) or 1/2" max. Do not spec 3/4" stone. It bridges between rebar and webs, causing voids (honeycombing).
* Slump: 5" to 6" (higher than standard walls) to flow around complex web geometry.
