Insulated concrete forms (ICF) are hollow blocks of expanded polystyrene that are stacked like building bricks, reinforced with steel bars and filled with concrete. The foam stays in place as insulation on both sides of the wall. This calculator counts the blocks and the concrete for a set of walls.
How the calculation works
- Net wall area = total wall length × height − doors and windows
- Blocks = net area ÷ face area of one block × (1 + waste), rounded up
- Concrete = net area × core thickness, plus 5% for spillage, form bulging and pump losses
- Courses = wall height ÷ block height, rounded up
A standard ICF block is 48 in long and 16 in high, so each block covers about 5.33 sq ft of wall.
Concrete per square foot of wall
| Core | Concrete per 100 sq ft of wall |
|---|---|
| 4 in | 1.23 cu yd |
| 6 in | 1.85 cu yd |
| 8 in | 2.47 cu yd |
| 10 in | 3.09 cu yd |
A 6 in core is most common for houses; 8 in and thicker cores are used for basements with high backfill, taller walls and commercial buildings.
Example
A house with 100 ft of walls, 8 ft high, and 60 sq ft of doors and windows has 740 sq ft of net wall. With 16 × 48 in blocks and 5% waste, that is 146 blocks, laid in 6 courses. A 6 in core takes 13.7 cu yd of concrete, or 14.4 cu yd to order with the margin.
Corners, bucks and bracing
- Corner blocks come as separate units; count them from the plan (two per corner per course) and deduct the same length of straight blocks.
- Door and window openings need wood or vinyl bucks.
- Walls need bracing and alignment systems during the pour, usually rented.
- Concrete is placed in lifts of about 4 ft with a boom pump and a reduced aggregate size (often 3/8 to 1/2 in), at a slump the ICF manufacturer recommends.
Thermal performance
The two foam faces, each about 2.5 in thick, give an R-value of about R-22 to R-25, and the concrete mass evens out temperature swings. Above grade, ICF walls typically meet energy code requirements without extra insulation in most climate zones.
Reinforcement, footing size and wall thickness must follow the manufacturer’s tables and the building code, or an engineer’s design.