“Building a world where we meet our own needs without denying future generations a healthy society is not impossible, as some would assert. The question is where societies choose to put their creative efforts.”

-Christopher Flavin

The Urbanization Issue

Many cities today are rapidly growing as time goes on. Despite their contribution to economic growth, urban areas increase carbon emissions, deplete natural resources, and threaten public health. Understanding how to build sustainable green buildings can help tackle these issues while supporting a growing population. We need to think about how we develop green buildings that would support our planet’s future.

A New Approach

In recent decades, Japan has positioned itself at the forefront of climate policy and green building. In the late 1980s, Fukuoka City was already looking to implement a framework to address climate change and sustainable urban growth. The population density of Fukuoka was rapidly climbing, and green space was on the decline.

Starting around this time, Fukuoka became known for its extensive scientific work on urban heating and microclimates, and its adoption of evidence-based environmental policies. Local governments enacted a municipal climate change plan in 1994, predating both the landmark 1997 Kyoto Protocol as well as climate action in other Japanese cities (Mabon 2019).

Putting Theory into Practice

Fukuoka’s premier green building, the ACROS (Asian Crossroads Over the Sea), is emblematic of the city’s larger fascination with sustainable urbanism.

Also known as the Prefectural International Hall, this example of green architecture lies in Fukuoka’s downtown financial district adjacent to Naka River and Tenjin Central Park.

ACROS was designed in the early 1990s by Emilio Ambasz and Associates, with the goal of lessening heat islands in the dense downtown districts. During the ACROS Fukuoka building’s development phase, the local governments in Japan integrated wider environmental considerations into previous legislation focusing on anti-pollution measures (Prefecture, 2017).

The city’s green space plan listed some of ACROS Fukuoka’s design goals. First, it included a mitigation plan for the heat island effect through urban greening in the city center. In addition, they wanted to show the relationship between green area and temperature.

Some controversy surrounded the building’s construction, since it threatened to encroach on Tenjin Park, the last remaining green space in the city center. To appeal to the public, Ambasz decided to integrate the site with Tenjin Park by designing a structure that incorporated both a building and a garden (Ambasz, 2020).

The Design

The ACROS Fukuoka building acts as a conventional office building that consists of 14 floors that contain an exhibition hall, museum, theater, conference rooms, governmental offices, private offices, and a basement. A semicircular atrium and a triangular-shaped lobby extrude out of the south side of the building.

On the ACROS Fukuoka Building, the terraced green roofs provide some of the following:

• Retain stormwater runoff
• Reduce pollutants
• Influence microclimates
• Improves air quality and absorbs greenhouse gases
• Provides insulation and reduces heating
• Improve the aesthetic quality of buildings and the urban environment
• Provide amenity and rehabilitative services (Elborambly, 2015)

The green roof also provides habitat for wildlife and birds. Originally, 76 varieties of 37,000 plants were planted. Due to the wildlife, a vast dispersal of seeds increased the biodiversity to 120 different varieties of plants. This external vegetation layer can lower indoor temperatures by one to two degrees Celsius (Fukuoka Prefecture, 2017). The combination of the residing park and the terraced green roof gives people an ideal location for exercise, meditation, and relaxation. On top of the roof, citizens can see a panoramic view of the city and Hakata Bay.

Let’s take a look at how this megastructure was actually built…

Construction Detail

Glass

On the north side of ACROS, each floor contains three different types of window glass: faceted glass, faceted & transparent glass, and transparent glass. The facet is a translucent material that presents a dynamic view to passing pedestrians and drivers. By keeping the top window faceted, it blocks people on the outside from viewing inside the building. In addition, the translucent glass allows light to enter in; hence, the faceted glass is on the top window of each floor. The bottom window of each floor is transparent, allowing occupants to conveniently view the outside environment. The middle piece blends functions of the faceted glass and transparent glass — slightly obstructing the line of sight from the outside, but allows occupants to vividly see the outside world.

As illustrated above, the facade is angled outward which creates an awning over the street and sidewalks. This effect allows the building to define the north entrance and to emphasize the megastructure’s urban presence.

The glass panes serve multiple functions to the building’s overall sustainability performance. Each type of glass has three layers to ensure the interior is quiet for occupants. Air gaps between each layer extract warm air to prevent heat buildup behind the glass. Overall, the diversity of the glass types on each floor reduces the use of ventilation systems and lighting control, mitigating the total energy consumption.

Concrete

ACROS Fukuoka utilizes reinforced concrete for most of its terraces and structural massing. In the opposite image, the exposed concrete corners are visible underneath the vegetation on each terrace.

Concrete is composed of cement, an aggregate such as sand or gravel, and water. Invented in the 1800s, Portland cement is a mixture of limestone and clay that is commonly used in modern concrete production (Concrete Design & Production 2019). Aggregates vary in composition and coarseness. Generally the particle size of the coarsest aggregates does not exceed 1.5 inches. Industrial processes involved in concrete production may include gravel mining and limestone quarrying (Schreiber 2020).

Since the design team wanted to reduce the building’s contribution to urban heat islands, they likely chose concrete for its thermal properties, among other factors. Concrete acts as a thermal mass, maintaining its temperature even as the surrounding temperature changes (Features and Usage 2012).

Concrete is a good choice for a building of this scale and complexity, but it isn’t the most sustainable material, since it emits carbon over its life cycle and is only partially recyclable (Concrete Design & Production 2019).

A Modern Lens

Twenty-five years after its introduction in 1995, ACROS has become an icon of Fukuoka, and a successful public venue. But has it lived up to its promise of sustainable urban growth?

We analyzed the performance of ACROS using a variety of indicators, including energy, water use, materials, and ecological functionality.

The LEED rating system:

There are various approaches to measuring the sustainability of a green building, but we chose to use LEED (Leadership in Energy and Environmental Design). The US Green Building Council created this rating system to define ‘green’ and encourage innovation. The LEED Building Design & Construction rating system awards a ranking (Certified, Silver, Gold, Platinum) based on credits allotted according to the categories below.

LEED BD+C v4, the most updated version, includes the following categories:

• Integrative Process
• Location and Transportation
• Sustainable Sites
• Water efficiency
• Energy and atmosphere
• Materials and resources
• Indoor environmental quality
• Innovation & Design/Regional Priority

This is our projected LEED score for ACROS Fukuoka:

Performance Overview

Sustainable Sites, Water Efficiency, and Energy and Atmosphere are the LEED categories most relevant to ACROS’s sustainability goals. This project focuses on promoting urban green space and biodiversity within a limited site. The roof also collects rainwater, which is stored for reuse in the toilets, and circulated to help cool the building. Heat island reduction was a major goal of the project, but only yields 2 points under LEED.

In terms of Location and Transportation, ACROS makes limited contributions to sustainability. It gets a few credits for its proximity to subway lines and varying land-use types, but any building on this site could receive these points. With a large underground parking structure and limited bike facilities, ACROS remains somewhat car-dependent but is easily accessible by pedestrians, and bus riders.

The Indoor Environmental Quality and Materials and Resources categories were not prioritized by this design. Street-facing facades and the atrium do provide good daylighting and quality views. It is clear that the experiential qualities were considered, but the environmental impact of material life cycles are likely less important to this design.

Energy use might be the weakest area of the building. With most windows facing north, ACROS fails to take full advantage of daylighting and passive heating potential. Despite its varying interior uses, this design doesn’t have a demand response system to adapt to varying energy use. The lack of renewable energy generation systems is also a huge missed opportunity, given the orientation and scale of the site. Despite this, ACROS still makes some progress, indirectly reducing energy consumption through its water and ventilation system.

Water

In terms of water, ACROS performs well. The green roof captures a majority of the site’s rainwater which is stored and reused for three purposes: HVAC cooling, noise-masking jets, and toilet flushing. Water is collected in pools located directly over the HVAC ducts, which lowers the air temperature inside the ducts and reduces cooling load. Collected stormwater flows down the terraces and into the building, which allows the site to consume less from potable water sources. Jets on the terraces spray excess water to improve aesthetics and mask noise from the city below.

This system does have some potential flaws. Since the project relies heavily on rainwater, a dry period could undermine the water use reduction normally achieved. In addition, the design has not been integrated with the adjacent river system and does not allow for groundwater recharge.

Design Translation

ACROS is known for its green roof and terraced fountains. As undergraduates at the University of California, Davis, we wanted to implement some of the design strategies from ACROS into our campus. We decided to adapt Ambasz’s successful stormwater system and green roof concept in order to propose improvements to two campus buildings.

Proposal #1

The current social science building is a bland, boring building on the West side of the complex. With a flat roof, this building serves no purpose functionally and socially for the UC Davis campus. Therefore, proposing a terracing green roof would significantly improve the site functionally and aesthetically.

By creating a terracing effect, water would be collected and drained through catch basins 6” above each bottom pool level, so water can be dispersed across the lower levels. In addition, remaining water can be released through a downspout onto a new vegetative area between the west entrances of the building. Adding an access point to the roof allows students to interact with the green roof and provides an overview of campus.

Proposal #2

Haring Hall is a sprawling two-story building with a large flat roof that directs stormwater straight to a drain. With a prominent central location, this outdated structure is one of the largest and most unattractive buildings on campus.

This proposal represents a more functional approach which mimics the water storage feature of ACROS. A sloping roof directs rainwater into a runnel system, which will flow into a rock channel on the lower level and be stored in cisterns for use in the building. Excess water will help irrigate a small vegetated roof with pollinator-specific plants. These improvements should reduce runoff, decrease Haring’s water use, and add ecological functionality to the site. The small green roof and visible water collection system can spread student awareness and spruce up the overall aesthetic.

A Green Legacy

Emilio Ambasz’s Prefectural International Hall showcases the reconciliation between commercial development and public desire for green space, meeting the needs of everyone involved with a building as iconic as it is innovative. This building equally blends in with the landscape of the surrounding park, water features, and cityscape. ACROS stands as an early example of modern sustainable design, successfully addressing the challenges of space efficiency and urban greening in a functional, beautiful, and experiential package.

Looking Ahead

Fukuoka’s rapid population growth continues to threaten open space and green coverage. ACROS represents one approach to this issue, but most developers do not have as much capital and such a robust design team. Another strategy involves retrofitting older buildings, which could be more feasible for smaller projects. Nevertheless, the city recognized the problem and is working to promote environmental adaptation into cities.

The ACROS Fukuoka building should not be the only model for green building design. Although it has flaws, we hope that similar approaches can be implemented elsewhere, with modern updates. As cities continue to grow, green design needs to become a priority to maintain our health, economy, and environment.

Written by Michael Siu and Zachary Skalak, University of California Davis

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