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 a reserve. 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 200 mm and more) and vertical bars stand every 600 mm and at each corner, with a lap into the footing.
Courses = wall height ÷ block height, rounded upBlocks = (L × H − openings) ÷ (l × h) × (1 + reserve)Concrete = (L × H − openings) × core width × (1 + reserve)Example
Walls 40 m long and 2.75 m high with 12 m² of openings and four corners, in 1,200 × 250 mm blocks with a 150 mm core, take 11 courses: 299 straight blocks and 44 corner blocks with a 5 % reserve, and about 15.4 m³ 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 1 m with a small aggregate mix and vibrate gently, so the forms do not bulge.
- Plan sleeves for pipes and cables before pouring, and fix window and door bucks firmly.
Questions and answers
How much concrete does an ICF wall need?
Core width times wall area: 0.15 m³ per m² for a 150 mm core, 0.2 m³ for 200 mm and 0.25 m³ for 250 mm, plus a few per cent for waste.
How many ICF blocks per m²?
A 1,200 × 250 mm block covers 0.3 m², so you need about 3.3 blocks per m². A 1,000 × 250 mm block needs 4 per m².
What core thickness should I choose?
150 mm is common for one- and two-storey houses, 200–250 mm for basements, retaining walls and taller buildings. Follow the structural design.
Found a mistake in a formula? Write to [email protected]