HNK, ROTTERDAM ALEXANDER

Status: project completed

From Grey Office Building to Living Green Landmark: HNK Rotterdam Alexander

Rotterdam Alexander. One of the city's busiest transport hubs, passed by tens of thousands of commuters every day. And above the office floors: four roof terraces that are now green with trees, shrubs, perennials and a 3D-printed bench that together form a single system.

HNK Rotterdam Alexander is a Paris Proof office building by NSI. The Urban Jungle Project realised a fully integrated rooftop garden across four levels (+1, +2, +3 and +7) - in collaboration with green partner VIC Landscapes, Cazdak, and construction party Constructif.

The Technical Challenge: Intensive Green Within 190 kg/m²

The central constraint of this existing building was precise: a maximum structural load of 190 kg/m² -significantly below the TUJP standard maximum of 250 kg/m², and well below what conventional green roof systems require.

Using Jungle Mix® ultra-lightweight substrate and fully custom-printed Jungle Blocks®, a rich, intensive rooftop garden was realised within those limits. Five multi-stem trees, more than twenty species of perennials and ornamental grasses, and custom-printed Borderbenches specially designed for this project.

Green and Furniture as One System

The Borderbench is a 3D-printed bench made from recycled post-consumer polypropylene - the same material and production technology as the Jungle Blocks®. Colour RAL 8017, rounded corners, two variants: a standard version and a lounge variant. Power sockets are integrated into the bench ends.

Green and furniture are no longer two separate systems placed side by side. The Borderbench wraps around the Jungle Blocks® organically. The boundary between sitting and greenery disappears - and at the end of their lifespan, both are 100% recyclable into new print material.

Biodiversity Through the Seasons

On the 7th floor, two multi-stem tree species stand in the Jungle Blocks®: Gleditsia triacanthos 'Sunburst', with ornamental yellow-green twigs, and Pyrus calleryana 'Chanticleer', which explodes in white blossom in April and turns fiery red in October.

The underplanting flowers in near-continuous succession from April to November. Sporobolus heterolepsis gives a subtle lavender scent in bloom and is a top species for pollinators. Calamintha nepeta ssp. nepeta is one of the richest nectar sources for bees. Geranium ROZANNE flowers from May to October. Echinacea purpurea 'White Swan' attracts bumblebees and butterflies. Verbascum x chaixii 'Album' is scattered as a candelabra accent plant throughout the planters. In winter, the grass stems of Sporobolus and Sesleria provide seed food for birds.

A Paris Proof Rooftop Garden as a Building Block

The building holds Paris Proof certification. The renovation of the building and the associated greening of four roof levels directly contributes to the energy performance, heat stress reduction and biodiversity value that this certification level requires.

On the 7th floor, the terrace functions as a daily outdoor workplace: lunch, informal meetings, individual work in green-enclosed open air above the Rotterdam skyline. Multi-stem trees of 350 to 400 cm are visible from the station and the adjacent office buildings.