Answer:
Depending on the geometric requirements of bricks, these are integrated into Class 1 to Class 4. All geometric requirements for the brick classes are listed in Table 3.1 of EN 1996‑1‑1. An example of assigning the classes according to the total percentage of the brick holes (% of the gross volume) is as follows:
| Class 1 (all bricks) | ≤ 25 |
| Class 2 | Vertical hole ratio > 25; ≤ 55 |
| Class 3 | Vertical hole ratio ≥ 25; ≤ 70 |
| Class 4 | Horizontal hole ratio > 25; ≤ 70 |
