Highly functional green rooftop guide for architects and design professionals

April 23, 2024

We believe it is vital to create functional urban green space areas. Areas that are not only ecologically beneficial but will support and enhance the wellbeing of humans.

Sustainable and highly functional solutions for green rooftops are becoming more and more sought after in the architectural world. Certification programs such as the United States Green Building Council’s  (USGBC) Leadership in Energy and Environmental Design  (LEED) program and BREEAM certification, are gradually encouraging more developers to include green rooftops in their architectural projects. It is becoming more of a requirement based on location. 

While selecting the right type of plants is a must, it is also crucial to look at functionality and sustainability as well when designing a green rooftop. Contemporary architecture must be sustainable, ecologically benevolent and highly functional while providing a pleasant environment for social interaction and personal well-being to humans. The use of organic, sustainable products is greatly encouraged.

In our article we will explore how three sustainable Black Locust architectural solutions for green rooftops can support stormwater management, combat urban heat island effect and provide urban green space recreational opportunities.

What is a green rooftop?

A green rooftop, also known as eco-roof is a roof surface that is partially or completely covered in vegetation on top of a flat roof over a waterproofing layer. There are two types of green rooftops: extensive and intensive green roofs.  

An example for extensive roof (left: light weight, non-accessible) and intensive roof (right: John W. McCormack U.S. Post Office and Courthouse rooftop with accessible Black Locust decking).

Extensive rooftop

Extensive rooftops are lightweight with a thin layer of soil, they provide stressful conditions for plants but are relatively inexpensive to build. Extensive roofs are usually visually simple, require little maintenance and watering and are usually not accessible to people. 

Intensive rooftop

Intensive rooftops provide favorable conditions for diverse vegetation as they have a deep layer of soil and a bigger structural load on the roof. They require frequent maintenance and complex irrigation and drainage systems. Intensive roofs can be visually very attractive, quite similar to wildlife conditions on the ground and act as urban green spaces that provide recreational opportunities for people. 

Green rooftop benefits

Green roofs have many benefits on society, climate and economy levels. Forward-thinking architects utilize green rooftops to keep buildings cool in the summer and warm in the winter. Other than regulating indoor temperature, they also play a part in rainwater management and storing. They also assist in reducing urban heat island effect, increasing biodiversity and providing recreational urban green spaces for humans. They increase property values and also save energy and reduce pollution. Green roofs are added to climate-proof buildings. 

Three highly functional and sustainable green rooftop features

To create a highly functional and sustainable green rooftop, it is advised to add features that will enhance stormwater management, ecological and recreational functions. This requires a green building material that will give a perfect flawless finish. 

Black Locust Lumber is becoming very popular for exterior use in architecture. It is the perfect type of wood for green rooftops. This is due to its water resistance, durability of 50+ years, and sustainability. Black Locust Lumber is naturally rot resistant and is a chemical free hardwood material that keeps its attractive appearance without the help of toxic chemicals or oils. When Black Locust Lumber is installed, it requires little to no maintenance which is a huge relief when you have so much other maintenance work to do with the biodiversity on an intensive green rooftop. 

  1. Green rooftop stormwater management with ProFlow™ permeable pavers

Green rooftops capture 80% of rainfall during storms while regular rooftops only collect 24% according to a study conducted by Pennsylvania State University, Center for Green Roof Research. Accessible rooftops will need some sort of hardscape for users to walk on. Architects, O’Donnell+Tuomey of Central European University rooftop used ProFlowPermeable pavers to cover their green rooftop to support stormwater management. 

Central European University green rooftop covered in Black Locust ProFlow™ Permeable pavements, completed in 2016, BREEAM status was achieved. 

ProFlowPermeable pavers allow water to soak into the pavement and the substrate layer underneath. This has a double advantage: permeable pavers reduce stormwater runoff and they also improve water quality by filtering out dust and dirt. Stormwater management features of ProFlowPermeable pavers help green rooftop projects qualify for USGBC, LEED and BREEAM certification programs.

  1. Reduce Urban Heat Island Effect with Black Locust decking

Cities with large amounts of paved surfaces absorb solar radiation and increase surface temperatures. This results in extreme heat, with temperatures being much warmer in cities than in rural areas. Green rooftops help combat the Urban Heat Island Effect by covering conventional roofing surfaces with vegetation. To take it a step further, extensive rooftops that are accessible to people use sustainable and cool surface materials to walk on and spend time around a newly developed recreational space. 

Before and after pictures of John W. McCormack U.S. Post Office and Courthouse Boston, MA achieved a LEED Gold certification with Black Locust decking installed on their green rooftop.

Andropogon Associates, the architectural firm, was responsible for transforming the 1933 Art Deco building. The John W. McCormack U.S. Post Office and Courthouse Boston, MA achieved a LEED Gold certification. The green rooftop is situated on the fifth story deck of this 22-story building. 

Since it is tucked between two towers, it is well shaded and perfect for recreational purposes of the building users. A Black Locust Lumber deck was installed for the use of office workers to lounge on during coffee and lunch breaks. Due to the light color and material properties of Black Locust, boardwalks and decking are a cooler alternative to concrete and other landscape surfaces, thus reducing the heat island effect. 

  1. Create recreational urban green spaces with site furnishings and planters

Green roofs can be a natural place for building users to spend some recreational time. Seating areas made of Black Locust wood provide an aesthetically–pleasing view and opportunity for social gatherings. They can green urban spaces like MIRA Tower in San Francisco by Studio Gang which aims towards the certification goal of LEED Gold. 

Black Locust Lumber site furnishings at MIRA Tower rooftop, San Francisco

Similarly 399 Fremont Street, a 122 m residential skyscraper in the Rincon Hill neighborhood of San Francisco, California has a beautiful green rooftop designed by architect Solomon Cordwell Buenz. The roof area serves the recreational needs of its residents of 452 residential units. 

Black Locust Lumber site furnishings at 399 Fremont Street skyscraper’s rooftop, San Francisco, California.

Another example to create recreational opportunities on green rooftops is by Via Verde in South Bronx, NY. The green rooftops designed by Dattner Architects use Black Locust Lumber planters and encourage gardening activities for residents, thus promoting a healthier and sustainable lifestyle. The initiative has gained a LEED Gold Certificate for its green rooftop. 

Black Locust Lumber planters at Via Verde rooftop in South Bronx, NY

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