• Over the past four years, there has been significant interest in "Optoppen" in the Netherlands due to the pressing housing shortage and the limited availability of new plots. Optoppen, which involves adding additional storeys to existing buildings, has been identified as a key strategy to address these challenges. The focus over the past three years has been to understand the potential of rooftops, tackle technical challenges, and overcome barriers. Currently, the Ministry of Internal Affairs, provinces, and housing corporations are collaborating to scale up Optoppen, particularly using timber. 
• The Central government has introduced multiple initiatives to stimulate and facilitate Optoppen. The launch of a platform to highlight Optoppen projects provides insights and requirements for successful implementation. More information can be found here: Coalition agreement and Governmental website Announcement.
• The letter by Minister Hugo de Jonge outlines a nationwide approach to promote Optoppen by facilitating, scaling up and standardising the process. It promotes topping up in Netherlands through progressive initiatives.
• There have been significant efforts taken by the government, housing corporation and other organisations which are summarised below:
  1. The province of Noord-Holland has introduced a €2.5 million subsidy for biobased Optoppen projects, including transforming building bases (uitplinten) and attaching apartments to building sides (aanplakken). More information can be found here: https://kvw3.kansenvoorwest.nl/Provincie-Noord-Holland-Klimaat-Circulair-bouwen-2.4.PNH.2
  2. The province of Gelderland has committed to support pilot projects and ensure faster construction of Optoppen developments. More information can be found here: https://www.gelderland.nl/nieuws/gelderland-zoekt-op-toppers
  3. The province of South-Holland has launched a rapid housing initiative through Optoppen, with subsidies for biobased construction projects dating back to 2022. More information can be found here:https://www.zuid-holland.nl/onderwerpen/ruimte/versnellen-woningbouw/optoppen-aanplakken-uitplinten/
  4. Efforts have been made to remove or mitigate regulatory obstacles, such as zoning plans, standardizing prefabricated units to meet building codes, and addressing parking space regulations. This has been developed in collaboration with five Dutch provinces and Aedes. More information can be found here: https://aedes.nl/media/document/handreiking-optoppen-10-delen-vermenigvuldigen
  5. A map has been introduced featuring legislation from various cities, serving as an example for clean construction practices.  More information can be found here: https://www.c40knowledgehub.org/s/article/Clean-Construction-Policy-Explorer?language=en_US
  6. A study focused on optimizing the use of existing buildings for residential purposes has been performed. More information can be found here: https://www.kences.nl/wp-content/uploads/2021/07/20210705-Platform31-Beter-benutten-bestaande-woningbouw-Onderzoek-naar-belemmeringen-en-kansen.pdf
  7. Continuous research efforts have been undertaken by TU Delft to explore innovative solutions for Optoppen. More information can be found here: https://www.delftsolardecathlon.com/

These collective efforts signify a comprehensive and multi-faceted approach to address the housing shortage in the Netherlands through the innovative strategy of Optoppen.