## 4 Results
### Voluntary Standards and Regulations  
There are many regulations set already that play a role within the MIS. For example, to unburden the sewer, the Rainwater Regulation forces SUD projects to be able to store at least 60 mm/m\({}^{2}\) of rainwater during heavy rainfall. Given this, findings indicate that there are multiple factors that challenge the incorporation of voluntary standards, as sustainability criteria, in GPP to achieve missions. These include the high number and type of stakeholders engaged over the duration of a project, numerous standards available by which to measure and promote sustainability within any given missions, uncertainty  
Figure 3: The PLABERUM process at the Municipality of Amsterdam [54].  
Figure 2: The role of the Urban Advisor during each program component of SUD projects [49]. Overall, they are responsible for connecting sustainability policy at the municipality with concrete projects, translating policy into practice, and giving feedback to policymakers on what is not working.  
on where or how to include standards within the project planning process, the relative nascency of sustainability requirements, fragmentation across districts, and variability between individual projects.  
The gradual strengthening of sustainability requirements in regulation means that eventually voluntary standards used in GPP will become law. For example, the lowering of Environment Performance Buildings (MilieuPrestatie Gebouwen, MPG) from 1 to 0.8 at the time of writing, and toward the end goal of 0.5. This allows for higher sustainability aspirations for non-public tender projects. Upcoming changes to legislation will facilitate the ability of municipalities to adapt policies to their own districts and give then more support in demanding improved environmental performance, together with a higher steering power from national authorities. The upcoming _Omgevingsweet_ (Environmental Act) was developed via input from all municipalities, and those with higher environmental aspirations could lobby for their missions to more strongly influence the act. Slated for implementation in early 2023, it is based on the National Environmental Vision (Nationale Omgevingsvise, NOVI) for spatial planning over the next 30 years. Issues are crosscutting over districts, developed as a single vision for environmental policy in close collaboration with provinces, municipalities, water boards, and social parties. It covers the construction of approximately 1 million new homes, with missions involving the use of more sustainable energy, adapting to climate change, the development of a circular economy, and the transition to circular agriculture. Each municipality will develop its own _Omgevingsvise_ (Environmental Vision), and one _Omgevingsprogramme_ (Environmental Programme) per subdistrict.  
Referred to by one respondent as \"a difficult new tool\", the _Omgevingsweet_ will simplify and merge the rules for spatial development to facilitate the beginning of construction projects, and as such will be the basis on which municipalities can increasingly refine or strengthen their sustainability requirements in SUD. This tool may accelerate the achieving of missions, particularly for non-tender SUD projects for which voluntary standards or GPP cannot be used to increase performance.