The Groene Mient residential project, located in the Vruchtenbuurt neighbourhood of The Hague, consists of 33 energy-neutral homes situated along a communal courtyard garden. The project has been realised in a collective private commissioning (CPO) and attention has been paid to, among other things; climate adaptation, biodiversity, energy neutrality and collectivity.
To limit flooding and desiccation caused by climate change, rainwater is collected locally and infiltrated into the soil.
On the basis of soil research by the municipality, it appeared that the soil is sufficiently permeable to infiltrate and measurements of the groundwater levels showed that these groundwater levels would not cause further problems.
Rainwater falling on the roofs and dense paving is drained into wadis in the communal courtyard garden. The size of the wadis is based on a possible future peak rainfall of 60mm/hour; they can collect about 112,500 litres of rainwater and slowly infiltrate into the soil. The wadis are interconnected by pipes (shown on the plan). During heavy rainfall, an adjustable float valve ensures that excess water is drained to a nearby ditch.So far (2017-2019), no overflow seems to have occurred.
Vegetated roofs of sedum have been realised on the roofs of the storerooms, which retain rainwater longer. In addition, the semi-open paving also allows rainwater to infiltrate under the residents’ parking spaces (gravel) and under the paths in the courtyard garden (crushed stone).
De Groene Mient was built on the site of the former school building of Maris College and most of the site was previously tiled. The quality of the soil was insufficient as a substrate for an indoor garden. By means of green manure and compost, the quality and water absorption of the soil was improved in the landscaping. For the indoor garden, permaculture principles are followed as much as possible; the garden is developed and maintained by the residents themselves, assisted by consultants.
Together with the municipality, the residents’ initiative managed to create a nature-friendly bank at the adjacent ditch. A nature-friendly bank is characterised by a variety of mostly native plants such as yellow lisse, big cattail, meadowsweet, big donkey’s head and queen’s weed that increase biodiversity.
In the context of sustainability, as many materials as possible that were released during the demolition of Maris College were reused in Groene Mient. For example, the roof beams were incorporated into the communal garden pavilion).
Preserved Douglas wood was used for the facade of the building.
The homes of Groene Mient are as energy-neutral as possible and built according to the basic concept that consists of: 3-layer glass, extra-insulated doors, 28 cm of insulation incorporated in timber frame construction with closed façade parts, high gap sealing, sloping roof insulation averaging 23 cm thick and PV panels for heating elements and lighting. There are also several homes with a heat pump, cold heat storage (KWO) source, shower heat recovery, additional pv panels and/or solar boiler combi with heat storage buffer tank.
The future residents of Groene Mient were keen to develop the project in an ecological way and managed to convince the Municipality that they could realise this themselves as a CPO project.
The neighbourhood initiative Groene Mient is a social, sustainable, energy-neutral and climate-adaptive housing project which has shown that it not only achieved a great increase in value for the neighbourhood on these points, but also an increase in property value. According to the WOZ valuation report, the value of a property increased by 15%. House construction budgets were estimated between €165,000 – €365,000 at the start of the CPO, the final construction cost at completion was ultimately between €155,000 – €265,000. Construction costs include installations < €1,000/m2 gross floor area incl. VAT. So climate-adaptive and energy-neutral building does not necessarily have to be more expensive.