Kumamoto Airport Passenger Terminal Building
“A Symbol of Earthquake Recovery”

Post-earthquake background
Nikken Sekkei first became involved in designing Kumamoto Airport as the architect for the Phase 5 expansion and renovation of the domestic terminal in 2012. This project included adding a single layer to the curbside area and improving environmental performance. It received the Building and Equipment Long-life Cycle Association (BELCA) Award, one of Japan's major architecture prizes that recognizes buildings that contribute to improving the quality of the built environment. The terminal building persevered through the 2016 Kumamoto Earthquake, which included two level 7 seismic intensity events, as well as numerous subsequent aftershocks. Although partially damaged, an overall assessment concluded that this was minimal to the building. However, due to severe damage to the boundary sections of the addition and the lack of reserve capacity in the base seismic strength, the Ministry of Land, Infrastructure, Transport and Tourism (MLIT) recommended a rebuild.

Rebuilding through airport concession
MLIT’s policy involved establishing a temporary terminal while rebuilding the existing terminal was based on a business proposal featuring privatization. We proposed earthquake resistance exceeding the required standards for the quakes that prompted the rebuild, along with eliminating the ceiling structure. This was due to the fact that after the prior quake, repeated aftershocks had caused cumulative damage in areas like the cavity ceiling, raising the possibility of sudden collapse. Ensuring the safety of the old terminal had become extremely challenging.

A rational construction plan
While privatization of regional airports in Japan had precedence, this terminal building rebuilds represented a first. Recognizing the challenging viability of the project, we proposed the following highly rational plan:
① Position the terminal at the center of the aircraft apron
② Extend the terminal depth to create a consolidated lounge areas for gates
③ Make a multi-gate lounge accessible to both domestic and international passengers
④ Establish a rational cross-section configuration via a mezzanine floor
⑤ Make economical spans + no basement + outdoor placement of core utilities
⑥　Optimize exterior wall openings and highly insulate the roof structure
These proposals were designed to achieve rationalization without compromising convenience, aiming instead to provide passengers with a user-friendly, enjoyable experience.

① Terminal positioned centrally, relative to the aircraft apron
Historically, domestic travelers have made up over 90% of Kumamoto Airport's passengers, with over 70% of domestic flights bound for Tokyo. The existing terminal had separate buildings for domestic and international flights, each with its own expansion areas, causing them to be significantly offset from the parking spots. Looking ahead, inbound travel is expected to compensate for declining domestic demand due to the decreasing population, with international flights seen as having growth potential. Therefore, the rebuild project aimed to place a unified domestic/international terminal at the center of the aircraft stands apron. Expansion plans for both sides were developed based on demand projections through 2052.

② Extending the terminal depth to create a consolidated lounge for gates
Instead of lounges for each gate, a large, open-plan shared lounge was designed. Space efficiency was achieved by considering the number of runways and flight schedules. To facilitate access to commercial facilities, the lounge frontage was narrowed without linking it to the boarding area, thereby securing greater depth. Consequently, the curbside road was relocated from its existing position during the temporary terminal period, enabling the gate lounge to achieve one of the deepest such layouts in Japan.

③ Stay-type gate lounge accessible to both domestic and international passengers (multi-gate lounge)
Designating commercial facilities exclusively for international passengers would result in low passenger density relative to volume, reducing its appeal. Therefore, the plan allows international passengers to use the domestic gate lounge after security screening. Furthermore, commercial facilities previously divided before and after security screening -- which passengers used while concerned about security congestion – were consolidated on the gate lounge side. This allows passengers to casually enjoy the commercial area from the point of early security clearance until just before boarding. Meanwhile, areas by local residents and for seeing off passengers are located on the first floor and in the separate commercial building (Sora Yoka Dining), which was completed in the second construction phase. These areas can be used in conjunction with the adjacent plaza (Sora Yoka Park), yielding “an airport where everyone who visits can enjoy themselves.”

④ Rational cross-section composition with two floors and an intermediate mezzanine level
The cross-section composition is simple. The first floor houses the ticket lobby and arrival lobby, with the departure floor above. Between them, a mezzanine level contains the mechanical equipment rooms, forming a rational “sandwich” structure that services both upper and lower floors. On the first-floor lobby side, the mezzanine level was offset to create a two-story height appropriate for the ground transportation hub.

⑤ Economic span + no basement + outdoor placement of core facilities
While large spans are often used in passenger terminals to ensure visibility, this design challenged the balance between an economical span and visibility assurance. Compared to conventional terminal designs, this simple cross-section and functional layout, combined with dynamic zoning, allows for passenger guidance that minimizes confusion. We eliminated underground mechanical rooms, placing large-area core facilities outdoors. This also ensures easy future upgrading and utilizes the extended pier as an above-ground trench.

⑥ Optimizing exterior wall openings and high insulation of the roof structure
By closing the south-facing curbside and opening to the north-facing air side, the impact of direct sunlight is minimized. Openings are positioned along the passenger flow direction, providing both light and guidance.　The domestic security checkpoint on the curbside features an opening only in front of the waiting line, reducing stress for people waiting, and allowing the ambiance of the third-floor wooden trusses to be felt from outside. The roof is also constructed with 100mm-thick insulated wooden sandwich panels. These aim to reduce energy consumption through the high thermal insulation performance of the building envelope.

A symbol of post-earthquake recovery through hybrid wooden framing
The new airport goes beyond terminal building functionality. As a symbol of post-quake recovery, it features a wooden roof structure that employs locally sourced Kumamoto timber, and so conveys this message directly and symbolically to passengers and visitors. Designed to offer visual appeal as well as the scent and aging characteristics of wood, residential-use 2x4 lumber was assembled into 10-meter length trusses which support the roof sheathing made from the aforementioned wooden sandwich panels.

To prevent lateral buckling, structurally engineered plywood with beautiful wood grain sourced from Oguni Town was used. The resulting cavities were utilized as ducts and equipment routes, integrating structure and systems to achieve an elegant, low-cost timber framework. Although this terminal building contains no steel, glass, large-span glass curtain walls or large openings, it aims to provide a unique passenger experience imbued with regional character -- an architecture worthy of memory for all who visit.

Location: Mashiki-machi, Kumamoto Pref.
Site area: 217,057.91㎡
Total floor area: 39,506.88㎡ (including Phase 2 construction)
Number of floors: Four above-ground floors
Eave height/maximum height: Eave height: 14.601 (m) / Maximum height: 21.251 (m)
)Main structure: Steel frame construction, partially wood frame
Completion month/year: January 10, 2023 (Phase 1), September 30, 2024 (Phase 2)

Credits:

Client name: Kyushu Kumamoto International Airport Co., Ltd.
Lead Architect: Nikken Sekkei Ltd
Main Scope: Concept plan, concept design, development design, supervision
Collaborative supervision: AZUSA SEKKEI CO., LTD. (Phase 1 only)
Construction Contractor: Taisei Corporation
Other collaborating design companies:
- Wayfinding: i Design inc.

- Interior design: D-Brain Co.,Ltd.

- Baggage handling system (BHS): AGP CORPORATION

- Construction Plan: Nikken Sekkei Construction Management, Inc.

- Landscaping: Miraifukeisha LTD.

Photo credit: SS Co., Ltd.