*3.5. High Motivation of Stakeholders for the Implementation of an ICU Concept but High Legal Barriers*

#### 3.5.1. High Motivation of Residents for a Sustainable Lifestyle

Current studies show that in Germany, a sustainable lifestyle becomes more and more important [78]. Today, 657 urban gardening projects exist in Germany [79]. However, the engagement of residents in urbane gardening might decline and require strategies to counteract. In contrast, a professional management of the urban gardening projects is more reliable, but often reduces the acceptance of residents [80]. A compromise could be combined models with hydroponic modules for the residents or a botanic garden with a cafe alongside professionally managed greenhouses.

### 3.5.2. Real Estate Owners would Implement the ICU Project as Long as It Is Profitable

Almost all real estate owners participating in this survey considered sustainable building as important for their business. Nevertheless, closed material cycles or exploitation of options related to the operation of AD or plant cultivation seemed less important for most of them. Some may even lose their tax benefits when they engage in another business field like urbane agriculture or operation of an AD. Therefore, it seems beneficial to outsource the operation of an ICU project to a contracting partner or a cooperative of the residents. Necessary conditions for implementing ICU concepts for real estate owners are high acceptance of the residents, lower maintenance requirements and profitability. Typically, there is no interest in pure flagship projects. Furthermore, especially for the roof-top use of buildings, ICU projects compete with other more established sustainable solutions such as the operation of photovoltaic systems (Supplementary File 8).
