REIMAGINING URBAN GREENSPACE OVER PARKING STRUCTURES
In the heart of Helsinki’s Töölö district, a major regeneration project transformed a closed construction zone into a vibrant urban park — sitting directly above a large underground parking garage. The rejuvenated Kivelänkatu Park offers an essential green oasis for residents, blending sustainability with engineering innovation.
To meet stringent weight limitations imposed by the underground structure, lightweight and porous Leca® aggregate was specified in the growing medium for the landscaped podium. This not only reduced load on the concrete roof deck but significantly enhanced water retention, drainage, and root support in a challenging urban environment.
FACTS
Application: Green roof-style park construction above parking infrastructure
Material Used: Leca® Crushed Lightweight Aggregate (3–8mm)
Project Overview: Green infrastructure, podium landscaping, urban tree planting, and load-sensitive sites
Engineering Challenge: Lightweight Landscaping Over a Parking Deck
The park, originally constructed in the 1970s, was redeveloped alongside a new multi-storey car park. The podium area required:
Low-weight growing media to avoid structural overloading
Durable green infrastructure capable of withstanding seasonal weather changes
Natural water retention and drainage to reduce maintenance and promote plant health
Due to weight restrictions, conventional construction plant was not permitted on the deck. All landscaping materials, including the lightweight growing media, had to be conveyed and installed using light equipment and belt systems — making material flow, consistency, and handling properties critical.
To meet the above challenges, a bespoke lightweight soil blend was used, combining:
Tieluiska’s Torpanpiha® Roof Garden Soil
Leca® Crushed Lightweight Aggregate (3–8mm)
Recycled brick aggregates
The addition of Leca® crushed aggregate delivered:
Low density (780kg/m³): significantly lighter than typical sandy soils (~1000kg/m³)
Enhanced drainage and porosity: promoting healthy root development
Improved water retention: reducing irrigation needs
Structural stability: Leca® particles don’t compact or rise to the surface in rainfall, ensuring a long-lasting growing layer
“With Leca® LWA, the growing medium becomes both water-retentive and free-draining — ideal for rooftop parks and green podiums,”
— Juha Liukkonen, Product Development Lead, Tieluiska Oy
A Hybrid of Heritage & Modern Sustainability
This unique project balanced urban sustainability with the preservation of historic landscape features, including:
Retaining an open rock outcrop used as a children’s sledding slope
Integrating existing mature trees with new tree and shrub planting
Using Leca®-based soil to support rhododendrons, azaleas and native woodland plants, creating a coherent naturalistic aesthetic
The combination of lightweight engineered fill with horticulturally tailored growing media allowed a complex site to become a vibrant and accessible greenspace — without compromising structural safety.
Conclusion
Kivelänkatu Park demonstrates how Leca® Crushed LWA plays a vital role in enabling green infrastructure in dense urban settings — where weight limits, drainage, and plant survival are all critical.
This project reflects a broader trend in UK cities toward multifunctional green podiums, with Leca® offering both the technical solution and sustainable credentials to meet the challenge.
