How it is calculated
The wall area without openings is divided by the face of one block to get the total number of blocks, plus extra. Each course has one corner block per corner, so corner blocks are corners × courses and the rest are straight blocks. The concrete is the wall area times the core width. Horizontal bars run in every course (two bars in cores of 8 in and more) and vertical bars stand about every 24 in and at each corner, with a lap into the footing.
Courses = wall height ÷ block height, rounded upBlocks = (L × H − openings) ÷ (l × h) × (1 + extra)Concrete = (L × H − openings) × core width × (1 + extra)Example
Walls 120 ft long and 9 ft high with 120 sq ft of openings and four corners, in 48 × 16 in blocks with a 6 in core, take 7 courses: 162 straight blocks and 28 corner blocks with 5 % extra, and about 18.6 cubic yards of concrete.
Tips from practice
- Brace the walls and check them for plumb before every pour: the forms cannot be adjusted once the concrete sets.
- Pour in lifts of about 4 ft with a 3/8 in pea-gravel mix and a 5–6 in slump so the forms do not blow out.
- Set sleeves for plumbing and electrical before the pour and fasten window and door bucks firmly.
Questions and answers
How much concrete does an ICF wall take?
About 0.0185 cubic yards per sq ft of wall for a 6 in core, 0.025 for 8 in and 0.031 for 10 in, plus a few per cent for waste.
How many ICF blocks per square foot?
A 48 × 16 in block covers 5.33 sq ft, so about 0.19 blocks per sq ft, or 19 per 100 sq ft.
What core size should I use?
6 in is common for above-grade walls of one- and two-story homes, 8 in and more for basements and taller walls. Follow your engineer and the IRC tables for ICF walls.
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