## 5 Discussion  
Results indicate that the Municipality of Amsterdam is actively engaged in implementing sustainability ambitions, with sustainability becoming an integral part of project development throughout the city. The majority of PLABERUM reports analyzed include chapters describing and outlining the sustainability requirements and ambitions for the project based on some of the six sustainability themes. However, others excluded a particular sustainability chapter if the project team considered sustainability already integrated throughout the whole report. Often, not all six sustainability themes were included, or, if they were, not all specific requirements and ambitions were addressed. For example, a new building project might refer to the sustainable energy ambition, fully including each variable and potential value of the mission (see Table 11, Appendix A), and only partly to the greening nature urban spaces and building nature-inclusive ambitions, including whether a green standard was achieved, at what value and with what specification, yet neglecting to discuss any (sustainable) lot management plan or nature-inclusive features such as nest boxes. Though it may not be desirable to deliver detailed information about all six sustainability themes, considering the high contextuality of projects, the current documentation was found to be insufficient and overly complex regarding sustainability.  
Still, during the analysis, many innovative sustainability solutions were identified to help move toward achieving the missions of the municipality. These innovative solutions address the environmental criteria determined by the municipality and sometimes went beyond what is legally required, serving as an (often de facto) voluntary standard. For example, the installation of solar panels combined with the use of highly insulating building materials can result in a building that is energy neutral or even energy positive, so that it can provide renewable energy to the grid. These types of solutions help to achieve the sustainable energy ambitions determined by the municipality to a large extent. Conversely, it also regularly occurred that a project only just meets the national requirements. Althoughthe national requirements are passable, they are almost never sufficient to meet the long-term municipal sustainability ambitions, as seen in the gradual strengthening of regulations over time.  
This significant difference can partly be explained by looking at the two main types of projects: public tender projects and non-public tender projects. These types of projects have some key differences in the way that solutions for a sustainability theme are determined. For _public tender projects_, the municipality can engage in GPP to challenge the market by awarding points to project developers that deliver more sustainable solutions, generating competition between project developers, whereas for non-tender projects they are bound by regulation unless additional agreements are made. Hence, sustainability themes are often addressed in much more detail and go further in tender projects. Projects for which GPP can be conducted, where the municipality is the landowner, more often include a wider variety of voluntary standards. However, by no means are the sustainability ambitions for _non-public tender projects_ less important, as this type of project is numerous, and the scale is often significant. In Amsterdam, only 20% of projects are tenders, whereas 80% are non-public tenders. While this reflects the greater impact of regulations on affecting the sustainability performance of technological solutions, it also suggests that in one-fifth of the projects voluntary standards have the opportunity to improve the sustainability performance even further. This creates space for GPP to reward companies with the best performance, creating both direct effects via implementation of these solutions as well as indirect effects through the market.