The formulas to calculate the length of horizontal bar needed are:

\[ Lb = 2.7 \cdot Aw \quad \text{(every 2 layers)} \]

\[ Lb = 1.9 \cdot Aw \quad \text{(every 3 layers)} \]

\[ Lb = 1.7 \cdot Aw \quad \text{(every 4 layers)} \]

Where:

• \(Lb\) is the length of horizontal bar needed (m).
• \(Aw\) is the area of the wall (m²).