*3.5. Connection between Vertical Indoor Greening and Reduced Sick Leave*

The results explained so far and the calculation results described below are summarized in Table 3. This table also shows the procedure explained in Section 2. In the following subchapters, the connection between the improved indoor conditions thanks to greening and the associated costs for installation as well as green care and technical maintenance and the possible savings due to reduced sick days are studied by different approaches.



For each of the considerations and the initial situations described below, the green area per workplace in the different rooms was used. It is dependent on the size of the installed vegetation as well as the number of possible workstations in the room under consideration. This results in costs for the greening per workstation. The respective values are shown in the Table 3.

It is to be pointed out again expressly that in the following considerations, only the improvement of the air humidity is used as reason, however numerous further reasons speak for indoor greenery, which were not considered in the context of the present investigations due to so far lacking data. In Section 4, these connections are explained prospectively.

3.5.1. Initial Situation: Profitability after Seven Years Using Linear Depreciation

For this first consideration, it is assumed that the greening system as a technical system is depreciated on a linear basis over seven years—the installation costs are therefore spread over 7 years. The costs for green care and technical maintenance are considered as annual costs.

Assuming a usage period of 7 years, the following statement can be made depending on the green space considered: From d days less sick leave per person, it will pay off to have greenery. The number of d days varies between 1.4 and 3.4 (Table 3).

3.5.2. Initial Situation: Profitability after A Certain Number of Years

In a further step, the following statement shall be made: "With a reduction of d sick days, the construction of the greenery is already paid off after x years".

To answer this, the annual costs for the greening per workstation are set in connection with the number of workstations in the room and the size of the greening and with the annual savings with reduced sick leave by a certain number of days at about 181 euros per day each. This can be calculated by the following Equation (1) and respectively Equation (2).

$$
w\_{\mathcal{S}\_{\mathcal{T}^{\text{reuc}}}^{\text{reuc}} \cdot \mathbf{x}} \left(\frac{\mathsf{C}\_0}{\mathfrak{x}} + \mathsf{C}\_{\text{carc}}\right) = \mathsf{C}\_{\text{sick}} \cdot d \cdot \mathfrak{x} \tag{1}$$

$$\mathbf{x} = \frac{ws\_{\text{green}} \cdot \mathbb{C}\_0}{\mathbb{C}\_{sick} \cdot d - ws\_{\text{green}} \cdot \mathbb{C}\_{carc}} \tag{2}$$

*x*—number of years; *Csick*—costs per sick day per person; *d*—number of sick days; *C*0 installation costs for greenery per m2; *Ccare*—costs for technical maintenance and green care per m2 and year; *wsgreen*—m2-greenery per workstation.
