About

MetroPolder company: The Polder of the City

Cities are growing and the climate is changing. With this comes heavy precipitation, extreme heat,  prolonged drought, and less urban space for solutions. The MetroPolder company revives cities through smart water management, leveraging stored rainwater for cooling, growing, and fostering nature within the city. MetroPolder is a leader in advising, developing, and maintaining smart water storage in cities.

Our philosophy:

Rainwater is a resource. Not waste.

Rainwater is often seen as waste. Rain is free and is the source of all life. By removing it through a gutter, we make it waste. This does not have to be the case. Rainwater is useful in the city. It cools, feeds plants, supplements groundwater, and can replace drinking water for many applications.  The most direct example being irrigating the roof garden above the polder roof system; no drinking water is needed and it provides greater biodiversity! A true win-win

Polder Roof®

MetroPolder company developed the Polder Roof® as a solution for flooding in cities. We are still developing, but already we are cheaper than traditional solutions (larger sewers, stormwater tanks). Cheaper and beneficial for the city which is also getting even greener, smarter and more livable.

What is the Polder Roof?

In order to make smart water storage on flat roofs possible, we developed the world’s first Polder Roof concept. The Polder Roof transforms roofs into smart, controlled, water storage. In this way, the system is able to store all rain that falls on the roof and to dispose of or use at a later time. The Polder Roof serves as the foundation for a green roof, rooftop garden, or solar park. The Polder Roof enables irrigation, infiltration or a connection to greywater systems.

How does the Polder Roof® work?

The Polder Roof consists of a buffer system, internet connected weir and an online dashboard. If necessary, the roof is equipped with an embankment, possibly supplemented by a complete water-separating layer. The Sm^rt Drop weir measures and regulates the water level and the run-off. Information about the roof and operating system can be accessed via your personal dashboard.

The team behind this innovation ensures that all roofs are continuously monitored and operated at optimal performance. The Polder Roof represents a new layer in urban water management!

The Perfect Foundation for Every Surface

The surface of the roof is protected with a buffer layer, which provides space to store the water while forming a solid basis for a choice of application on top – from solar panel to roof park, from pavers to colorful floral mix.

Click here for the product sheet Polderdak® (SI units)

Automatic Retention Control

Polder Roofs are controlled by the Sm^rt Drop: a small weir which maintains the water level and a set of sensors to ensure that the system always functions safely.

Click here for product sheet sm^rtDROP (SI units)
Click here for product sheet sm^rtDROP (US customary units)

Online Dashboard

 We measure, report, and display everything we need to know to safely store (temporary)  water on the roof.

Click here for the Dashboard

A Regional Solution to Stormwater Management

Together with cities and universities, we work to transform urban centers into a smart grid for water. Call this a rooftop water-board. Resilio is an example of this.

Click here for Resilio’s website

Services

Planning phase: The Roof Plan

During Design: Building Advice

Roofs offer opportunities for the climate adaptation of your municipality, region or development area. Many municipalities see these opportunities, but wonder where and how best to start. The Roof Plan can be drawn up at regional or property development level. With a Roof Plan:

• We determine where the possibilities for water storage on roofs exist
• You will immediately get practical tools for yourself and to work with other parties (private individuals, companies, housing associations).

For whom? Governments, City Planners, Water Boards, Housing associations

You want or have to store water on your lot, from the building envelope or sustainability policy/ambition. We will help you with a (winning) design that can also be executed:

  • Water storage advice: We will design to meet your water requirement or wishes (in VO or DO phase)
  • Engineering: We ensure that the water storage is properly secured in the construction or renovation process (in DO phase)

For whom? Developers, Architects, Contractors

During Construction: Setting Smart Weir

During Operating Phase: Management and Maintenance

The Polder Roof is built by an installation partner of your choice. We work with various local roof gardeners.

  • The sm^rtMILL or sm^rtDROP is installed by the roof contractor, MetroPolder provides the right settings and accessibility to the online dashboard
  • If desired, we will take care of a control of the Polder Roof during or after installation

For whom? Contractors, Green Roof Professionals

We maintain water storage, give you insight and if desired we report on your water performance:

  • Annual maintenance
  • Insight into performance through our dashboard and annual reporting
  • Data management

For whom? Roof Owners, Administrators

Projects

Click on the images below to view the projects.

Team

Joost Jacobi
Project Developer

Merle van der Kroft
Consultant

 Matthijs Monkelbaan
Engineer

Jenno Vos
Maintenance and installation

Friso Klapwijk
Director

Brian Schmitt
Project Developer

Bram Vulperhorst
Consultant

Joris Hooftman
Monitoring and IT

Contact

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    FAQ

    About water storage in the city

    Why would I want to store water on my own property?

    More and more municipalities are setting requirements for new construction projects. In 2021 Amsterdam enacted the “Hemelwater Verordening” or rainwater regulation, which sets requirements relating to rainwater retention for all construction requiring a permit. In existing construction, more and more are looking for ways to retain more water to protect foundations, nurture trees and thus make a greener healthier city.

    Can a neighborhood go without sewers?

    Residential areas used to have one sewer pipe for both domestic wastewater and rainwater. In the Netherlands, about two-thirds of all sewer systems are still mixed. This means that during heavy precipitation, dirty wastewater ends up in ditches and canals. Since the late 1990s, new housing estates have increasingly been built with separate systems: a pipe for household wastewater and a pipe for rainwater. That was already a step forward.

    However, we are increasingly discovering that rainwater is very useful for retention: replenishing the groundwater in summer, cooling and feeding nature in the neighborhood: rainwater is valuable. In the meantime, technology has also reached the point where a building, building block or neighborhood can be constructed without rainwater sewers.

    Is it possible to apply for a subsidy for the construction of your own water storage?

    This varies per city, municipality and country. But more and more municipalities are providing subsidies for construction. In the Netherlands there are national plans to reduce your water taxes if you collect all your rainwater on your own property. Contact MetroPolder for advice regarding the subsidies in your specific country and municipality.

    Is it wise to store water on the roof?

    First of all, if rainwater can be infiltrated directly into the soil and there is room to create a sufficiently large infiltration facility to accommodate heavy showers, then that is always the cheapest and simplest option. In practice, however, there are many situations in which there is either no space in the ground or a high groundwater level in winter or very little infiltration capacity, where it is still necessary to find a solution in or on the building. MetroPolder always looks for the best system design in the trade-off between objectives, requirements and cost per m3.

    If the design of the building also includes a roof garden, then applying water storage as the basis of the roof garden is always a good choice: by creating an artificial groundwater level the plants flourish better and a greater variety can be realized on less package thickness (= weight).

     

    About Polder Roofs

    What requirements must the roof meet to install a Polder Roof?

    The (temporary) storage of rainwater on the roof also requires a good design of the roof, not only the construction, but also the roofing system and the connection (the detailing). In a general sense, a fully adhered system is used as standard where all layers including the insulation fully adhere to each other. Always ask your roofing partner or let MetroPolder advise you further.

    What is the difference between blue roofs, retention roofs and a Polder Roof?

    There are several terms used interchangeably for water storage on roofs. The term blue roofs is often used in the context of multifunctional roofs, where blue represents water storage. Retention roofs are often used as a collective term for various types of water storage roofs, where the Polder Roof® represents smart water storage roofs. The Polder Roof® is a registered trademark of MetroPolder.

    What does a Polder Roof cost?

    The cost of constructing a Polder Roof is around 700,- per m3. Upkeep is less than one euro per m3.

    Can a Polder Roof be used in combination with solar panels?

    Yes, certainly. The stored water provides cooling and thus 6% higher efficiency of the solar panels.