Council on Tall Buildings and Urban Habitat

The Hansar, Bangkok
Written by Richard Hassell, Wong Mun Summ, and Alina Yeo, WOHA
Posted February 2012
This paper was originally featured as a case study in CTBUH Journal 2012 Issue I and is also available as a PDF download.The Hansar was recognized as a finalist in the 2011 CTBUH Awards Program.
Other Featured Tall Buildings
“The Hansar provides a series of skillful connections to nature, both on its exterior facade and in the interior spaces.”
Richard Cook, CTBUH 2011 Awards Chair, Cook+Fox Architects

173 m (567 ft)
Primary Use
Hotel / Residential

Somhansar Company Limited
Ativa Hospitality Corp., Ltd.
Design Architect
WOHA Architects
Associate Architect
Tandem Architects
Structural Engineer
Warnes Associates Company Limited
WSP Lincolne Scott
Project Manager
EMS Consultants Company
Ritta Co. Ltd.

High-rise, high-density living has been embraced as a positive housing solution for many millions of people living in Asia’s growing urban metropolis. WOHA have designed a series of buildings for South-East Asia that expand the way highrise, high-density living is conceived. Based in equatorial Singapore, WOHA have firsthand knowledge in designing for the tropics with The Met, The Hansar, The Pano, 1 Moulmein Rise and Newton Suites being prime examples of their works. Approaching the design from lifestyle, climate and passive energy strategies, the towers are radical yet simple, and show that the concept of a tropical tall building as a naturally ventilated, perforated, indoor-outdoor, fully shaded furry green tower is central to tropical living and a necessary alternative to the temperate models of sealed, glazed curtain wall buildings being erected across the tropical regions. This case study focuses on The Hansar, a 45-story hotel and residential development that embodies principles of sustainable and tropical living within dense urban cities.

Introduction & Site Context
The Hansar is a crown property located in the heart of Bangkok adjacent to Four Seasons Hotel, which is the city's leading commercial, retail and entertainment district. It is surrounded by major shopping areas, a large city park, high end condominiums and luxury hotels. The development, being conveniently sited within walking distance of the Rajdamri BTS station, encourages a practical way of dealing with Bangkok’s urban sprawl and severe traffic jams by permitting higher use of the city's existing public transport infrastructure, its privately run elevated walkways and improved pedestrian network. Achieving a building plot ratio of 1:10 on a small and irregular site, the design maximizes the building area while contributing to the urban environment with its lively street retails frontage at ground level that engages pedestrians, encourages walking about the city and entices passers-by into its restaurant, bar and outdoor dining garden terrace.

A Humanist Response
Tall buildings in the temperate West evolved as a type that embedded its technological solutions in its DNA. The harsh climate of Chicago and the economic pressures of New York created the modernist tower as an engineered solution, compact cantilevered columns, with maximized volume to surface area ratios, wrapped in smooth shiny skins, with inhabitants kept comfortable mechanically. Aesthetically, culturally and philosophically, these are heroic corporate structures that jostle for height, status and domination of nature through technology. As tall buildings scale and human scale are vastly different, the challenge of high-rise residential towers is to address the alienation of tall buildings by emphasizing on the individual in terms of human scale, choice and comfort, while opening up to the climate, community spaces and nature.

Over the last six years, WOHA has investigated into the quality of external spaces in high-rise towers such as The Met, The Pano and The Hansar in Bangkok. In designing The Met, a 69-story high rise residential tower, a series of gardens and inhabited external spaces in the sky were developed. Community areas with covered walkways, open-air living areas, sky gardens, barbecue stations, library, fitness corners and recreational areas were created at strategic horizons every 20 stories, giving all the residents access to high-level views and open-air communal terraces, while private gardens designed with swimming pools and terraces were incorporated every six stories, effectively creating miniature garden houses downtown, each with its own little plot in the air throughout the height of the tower. Pockets of cantilevered sky-gardens adjacent to lift lobbies throughout the tower height also allowed all residents to enjoy the spectacular breathtaking high-rise views over the river and city.

Figure 1. Entry Approach

The Hansar was initially conceptualized as a hospitality and residential development. The program was changed mid-way through the design into a fully residential building, but due to its short lease of 30 years and central location advantage, it was ultimately a better business investment proposition to revert to the original brief comprising hotel and condominium (with concierge) components.

Under this final direction, the two co-existing program were eventually developed as clearly distinct components in their planning and operations, but unified in their architectural treatment and form. In The Hansar, landscaping was additionally employed to introduce visual cues to scale. Every apartment unit within the rear square residential tower was designed with either a private lift lobby that comes with an entry to the sky garden or a living room with sky garden views. These cantilevered sky gardens are common spaces that project off the lift lobbies at five-story intervals and are planted with mature frangipani trees that frame the city views and create dramatic yet human-scaled external spaces in the sky. They also serve as a delightful physical buffer between the apartments, which are thoughtfully designed with windows that focus the gaze into the sky gardens and prevents overlooking into the neighboring unit, thus enhancing the privacy and exclusiveness of the residences. 

Figure 2. Typical hotel room with green wall

Response to Climate
The Hansar is designed according to the concept that a naturally ventilated, perforated, indoor-outdoor, fully shaded furry green tower is central to tropical living and a necessary alternative to the temperate models of sealed, glazed curtain wall buildings being erected across the tropical regions. The Hansar rejects this model, and instead transforms and adapts vernacular and passive responses to climate into the high-rise form and contemporary technologies, with the same aim of creating comfort without the need for mechanical systems. The challenge is to open up the high-rise and bring fresh air and nature into a building, enabling it to breathe within an extremely dense mega-city so that quality living in high-rise buildings are achieved in an imaginative and sustainable way that is authentic to the context of its region, climate and locality.

Therefore, rather than adopting the strong separation of interior and exterior that is characteristic of temperate models, The Hansar explores how aspects of low-rise tropical housing can be applied to create outdoor-indoor spaces in the sky. By organizing the units around a central core and courtyard, coupled with cutting vertical slots with pockets of sky gardens throughout the building height, cross ventilation of all the apartments and natural ventilation of most bathrooms is achieved. This block arrangement gives all apartments access to light and air on all sides, making possible living without air-conditioning. Most apartments are also designed with balconies provided across its frontage. This works in combination with delicate sunshades to keep the interior cool at all times. The condominium apartments and hotel rooms are all accessed off naturally ventilated and naturally lit corridors, reducing the energy use of the building substantially. 6 stories of car parks are contained within the low rise block service the development. These carpark levels are elevated to avoid Bangkok's frequent floods and is a more sustainable approach to building deep basements. Concealed behind porous breathable walls of draping greens, cross ventilation and natural lighting through the car park levels are simply and effectively achieved.

Figure 3. Metal mesh screens serve as the building's outer skin

A porous façade in the form of a metal mesh screen was designed to hang off projected ledges at every floor, serving as the building's outer skin that regulates light and air throughout its fully shaded vertical surfaces. These external sun screens, which overlap with the inner window layer of the apartments, also function as privacy screens, create foreground that frames the city views from within the units and reduce the dependency on interior window dressing. Its staggered placement generates visual interest from the exterior while neatly concealing air-conditioning condenser units and services behind. The sun screens are specially coated in a metallic bronze color, its golden sheen and floating greenery alluding to the glimpses of gilded Thai temples and luxuriant gardens that hide amongst the concrete jungle of Bangkok. This strong juxtaposition against Bangkok's backdrop of dull colored buildings and grey skies gives the development its uniquely distinct character, and is a refreshing addition to the city skyline.

Highrise External and Community Spaces
Given the increased stress on the ground level caused by the rapid growth of urban densities, the design approach treats the ground plane as a duplicable layer of the city that needs to be replicated at strategic horizons within buildings. This involves the introduction of intermediate levels comprising social and community functions, serving as multiple ground levels in the sky. The layering arrangement also creates opportunities to achieve dynamic visual links between the buildings and generates multiple covered tropical outdoor spaces.

Structural System

The Hansar's tower structure comprises of a simple concrete reinforced frame around a rigid central core. Connected to the hotel slab block at the low rise zone, a broad and stable base is achieved for the residential tower that steps back as it rises. Structural engineering is fully integrated with architectural design. To maximize space within the apartments, all columns are externalized on the face of the tower. These columns which reduce in size as they rise, are strategically positioned within the unit's utility zone (AC ledge), and are fully screened from public view by the architectural mesh screens. Sky gardens not only serve to bring green relief but also structurally tie together the four individual slender tower blocks at every fifth floor, thus increasing the overall rigidity of the building.

Figure 4. Glass Detail 

The Hansar presents an innovative solution to the issues of density in tropical Asian cities, and offers a new model for tall building design that is sustainable and suitable for high-density tropical living. A refreshing urban oasis nestled amidst the congested metropolis with its calm draping green facades, hanging sky gardens, floating sky pavilions and delightful golden screens glimmering iridescent in sunlight, The Hansar lifts not only the blanket of Bangkok's polluted grey but also the spirits of its urbanites, as evidenced by the many positive public feedback and commendations it has received to date.

Related Links
CTBUH Skyscraper Center Profile:
The Hansar

The Hansar was recognized as a Best Tall Building Finalist in the 2011 CTBUH Awards Program.
Download the The Hansar 2011 CTBUH Awards Book section

2011 CTBUH Awards Book

CTBUH Journal 2012 Issue I:
Download the Paper

The CTBUH would like to thank WOHA for their assistance with this article. Photography WOHA / Patrick Bingham-Hall.