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.