The Rainbow Tree by Vincent Callebaut Architectures

A multiple architecture revealing the cultural and natural filipino heritage
In the heart of East Asia, Cebu, in Cebuano Sugbo, is one of the largest islands in the Philippines. On October 31, 2019, the United Nations Educational, Scientific, and Cultural Organization (UNESCO) designated 66 new “Creative Cities”. Among them is Cebu, awarded for its innovation in design, particularly in the field of fashion, architecture, and the production of eco-responsible furniture.

The objective is to construct a residential building with double environmental certification (LEED + BERDE) which offers the perfect balance between mixed cultural heritage and natural heritage of unparalleled splendor. At a time when we need to find radical solutions to reduce the global carbon footprint, we have designed a 32-story, 115-meter high tower built of solid wood, as it is the only natural, abundant, and renewable material.

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This organic tower integrates the principles of passive bioclimatism and advanced renewable energies. “The Rainbow Tree” tower is adorned with the most beautiful plant essences from the neighboring tropical forests. This luxuriant dress of more than 30,000 plants, shrubs, and tropical trees draws a flourishing spiral in the colors of the rainbow and brings a breath of freshness to the heart of Cebu Business Park which is mainly built of concrete and steel.

A modular mass timber tower inspired by traditional “Bahay Kubo” homes
The Rainbow Tree is a staggered geometric stack of 1,200 modules, each with sides measuring 4 meters sides and a height varying between 3.2 to 4.8 meters. All these mass timber modules are prefabricated and standardized in a factory with a very high degree of precision. They are directly inspired by the “Bahay Kubo” (literally, cubic houses, also known as “Nipa Huts”). These indigenous nomadic houses were made of natural materials from the forest such as wood, bamboo, and palm leaves.

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These bio-based “Bahay Kubo” breathe! They are in symbiosis with nature. Their architectural identity reveals that they are based on ventilation, large open interior spaces, and terrace networks adapted to the tropical climate. These three foundations are the basis of our architectural concept for building a CLT (Cross Laminated Timber) tower. Invented in the 1990s in Austria and Germany, this construction technique consists of superimposing perpendicularly wooden slats and connecting them together using structural, now-organic adhesives such as tannins, lignin, cellulose, or even starch.

Being built from trees cut and harvested in short circuits in the archipelago in the heart of eco-responsible forests – where a cut tree is equal to a replanted tree – means that the Rainbow Tree is a real carbon sequestration well. In fact, during the growth of trees through natural photosynthesis, the stored carbon is found “trapped” in solid wood and is therefore not released into the atmosphere. For 1 ton of wood produced, about 0.9 tonnes of carbon is confined. This means we are talking about a building with a negative carbon footprint!

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Flexible design for mutable and reversible programming
The CLT structure consists of a central core, also made of mass timber, and an “exoskeleton” facade completely freeing the accommodation and amenities of any load-bearing wall, intermediate column, and sheath in the center of the plates. This design frees up space to allow each resident to personalize their apartment. Wooden balconies cover the 115 meter high Rainbow Tree. They are basket-designed with structural consoles in facades allowing the loads of the planters to descend naturally to the trunk of the tower like the branches of a tree.

Programmatically, the Rainbow Tree is subdivided as follows:

• In the basement, from level -1 to -3, there are 40 parking spaces per level, or 120 spaces in the infrastructure.
• On the first floor: a catering restaurant, a coworking flexible space , the large entrance hall of the accommodation, and the bicycle parking.
• 2nd floor: co-working office space and access ramps to the silo car park.
• From the 3rd to the 6th floor, 40 parking spaces per level, or 160 spaces in superstructure for electric cars.
• On the 7th floor, the condominium pool and spa.

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• On the 8th floor, the mezzanine of the fitness center offering a double height over the swimming pool.
• From the 9th to the 31st floor, 13 apartments per level with the 3-bedroom apartments in the corners, or 300 apartments (138 Units – 1 Bedroom / 115 Units – 2 Bedrooms / 47 Units – 3 Bedrooms).
• On the 31st floor, an urban sky farm and its 2 mezzanines aquaponically producing fruits, vegetables, and algae harvested in an extra-short circuit by the inhabitants of the Rainbow Tree.
• On the roof, 1,650 m² of photovoltaic and thermal solar panels

Burnt wood facades, the ancestral beauty of “Shou-Sugi-Ban”
Outside, the blond wood of the CLT gives way to black-silver wood. In fact, the tower is covered with a cladding of cedar planks burnt according to the ancestral Japanese method called Shou-Sugi-Ban. This wood bears the name of Yakisugi (焼 杉 板). Yakisugi is obtained by deeply burning the surface of wooden planks. This material, mainly used for individual houses, is reputed to be more resistant to fire, wood-eating insects, and lignivorous fungi. Four layers are distinguished (from the outside to the inside of the facade): carbon, tar, pyrolyzed wood, and solid wood which are not affected by heat.

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Esthetically, the tower is thus dressed in a scaled dress with a silver patina and bluish reflections. The traditional Yakisugi technique aims for high environmental quality without any use of synthetic chemicals and without the use of any additional energy source, such as gas. The burnt wood facades are inseparable from the Japanese esthetic of Wabi-Sabi: the fruit of several natural processes – photosynthesis and fire – they age over time, and this change in appearance is positively perceived by people who see it. The spirit of Wabi-Sabi means accepting the imperfect surface of the material that accompanies the life of the residents.

Multi-colored, carbo-absorbing, and depolluting balconies
The Rainbow Tree has sinusoidal balconies staggered between the even and odd floors allowing palm trees and deciduous trees to grow on a double height. The endemic plant species are listed according to the color of their flowering – pink, purple, green, yellow, orange, red – to draw 5 plant spirals wrapping around the solid wood facades.

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This urban forest makes it possible to fight against the effects of urban heat and constitutes a true island of freshness by the evapotranspiration of plants bioclimatizing naturally the public space. In addition, the 30,000 plants, shrubs, and trees planted on the tower will capture 150 tons of CO2 in the atmosphere of the Cebu City annually to transform them into oxygen through natural photosynthesis. The tower, which is already low in intrinsic carbon thanks to its bio-based construction materials, will also be breathable and depolluting during its operation.

A passive construction integrating urban agriculture and renewable energies
The tower benefits from double insulation – interior and exterior – and from natural materials such as thatch, hemp, and cellulose wadding. In addition, the plant cover makes it possible to control the solar gains and take advantage of the evapotranspiration of the plants to cool the temperature felt on the balconies by 2 to 5 degrees. To ensure natural ventilation in each apartment, wind chimneys cross the central core over its entire height.

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In addition to the vegetable tubs planted on the balconies of the apartments, an urban aquaponic farm is spread over the last three levels of the Rainbow Tree, a technique of sustainable and virtuous agriculture that combines fish farming and plant cultivation and allows you to experience the countryside in the city by removing social ties. The Sky Farm produces 25,000 kilos of fruit, vegetables, and algae and 2,500 kilos of fish per year, or almost 2 kilos of food per week for each family residing in the tower. These foods are grown with a water saving of 90%, without chemical fertilizers, pesticides, or GMOs, but from natural fertilizers. In fact, fish excrement nourishes the plants with nitrates. This absorption then filters the water.

A “living market” will allow Cebuanos residents to not only buy farm products but also to eat them on the spot in a cozy atmosphere. This urban farm is covered with a solar canopy producing electricity stored in hydrogen fuel cells and domestic hot water redistributed in a virtuous loop in the bathrooms and kitchens of the apartments. To top it all off, a farm of 16 axial wind turbines with magnetic levitation also generates electricity in situ without any noise pollution. Source and images Courtesy of Vincent Callebaut Architectures.

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