The Floating Gardens
of Shore Street
Romain Legendre _________ Young Architects Competitions Kiribati Floating Houses (2020)
The inhabitants of the Kiribati Islands maintain a strong communitarian way of life. As connection between everyone, the traditions have a great role to play, and among them, agriculture. _________ Insuring the durability of the food production system and the associated know how is insuring the capacity of reconstruction and durability of the community. Shore Street promotes the gardens as part of two ecosystems : a biological ecosystem, and a social ecosystem. These two aspects meet each other in the conception of multifamily housing units around the Floating Gardens.
-- Shore Street -social ecosystem
As a comunitarian catalyst, the floating gardens are inserted in an agregation of farms built above the water and connected by a main axis : Shore Street.
Congregated buildings in Tawara Island
In the Kiribati Islands, the ground is a precious ressource, and Tawara is representative. Shore street chooses to priorise certain uses on it, like palmtree groves and construction workshops. As the ground is scarce and crowded, having space is a luxury. In Shore Street, the domestic spaces are large and simple, built above the sea and its later reached level, establishing a strong connection with the water. Shore street follows the strong shape of Tawara Island  : congregated buildings along an axis connecting everything. This way, it can be extended and connected to the ground as the houses rise.
Shore Street transversal section BB’ - 1/250
Shore Street 1/1000
B’
B
Mwaneaba
Breakwaters
Housing unit
Workshop
Social axis
community house used for events
damaged palmtrees
multifamily house for 8, 16 or 24 persons
construction place for the timber and coconut work
public passage connecting houses and domestic workshops
-- Stilted Farm -social ecosystem
henhouse
workshop
bedroom
A
bedroom
bed room
bed room
bath room
bath room
bed room
bed room
bedroom
bedroom
storage room
technical room
outdoor gathering space
gathering space
kitchen
A multifamily housing unit - 16 inhabitants ground floor - 1/250
The protected floating gardens transversal section AA’ - 1/250
A’
The housing unit is conceived like a built ring surrounding and protecting the floating gardens. This shapes enhances the communitarian aspect of the Kiribati’s way of life. Each part of the building is dedicated to a specific aspect : manual activities on the landside, shared living spaces in front of the ocean, and intimate rooms on the lateral parts. They all surround the core of the unit, the aquaponic systems, protecting it against strong winds and waves. The house is integrated to the community by the main axis connecting every unit and leading to the ground.
-- Local (im)material richness -biological and social ecosystem
RENEWABLE RESSOURCES Using the local materials, the renewable ressources of the Kiribati are the one to be developped firstly. They find sense perpetuating the local know how and the building traditions, as well as stimulate the activities for the inhabitants of the islands.
Coconut trees The coconut trees are an important ressource in the Kiribati Islands. The palmtree groves can help fixing the ground of the island against the erosion from the ocean streams and the wind. More than an activity for the inhabitants, the coconut tree provides many subproducts possibly used
Pandanus trees for construction. The trunk is used for construction timber, the palms to make fabric or roofs. The coconuts produce food and fibers, used as isolation and potentially transformed into strings or fabric. These materials are used for traditional building technics and are the fruit of a local expertise.
The pandanus is a common tree in the Kiribati Islands. It can be used to make small construction timber, and woodplanks. As for the palmtrees and the coconut products, the work needed has a traditionnal background for the Mwaneabas and can weld the community.
RECYCLED RESSOURCES
IMPORTED RESSOURCES
On the islands, other materials can be recupied and among them, some can be reused, helping reducing the consumption of building materials while cleaning the lands.
As they have a heavier carbon impact for their transport, their uses must be limited.
Plastic and other debris
Damaged trees
Construction materials
Lots of debris can be found on the beach of Kiribati Island. Some can be recupied and used for construction or systems (planters, floating devices...) after a cleaning process.
With the harsh weather conditions, many trees are damaged : strong winds or high tides can kill palmtrees. The trunks left can be used not for construction but as breakwater.
Some construction materials have to be imported from other part of the world : metal components, new plastic pieces or solar energetic technologies for exemple.
The manual work, be it agriculture or construction, has a great social value in the Kiribati community.The know-how is symbolic of an important role in the society. The collective construction of the living spaces is fundamental in the constitution of the sense of belonging in the community. Every one insure a specific part in the transformation from primary product to final material.
-- A protective enclosure -social ecosystem
Primary structure palmtree pillars planted in the seabed, stabilized with doubled beams, and traditionnal strings assembly
Secondary structure light pandanus timber supporting the roof and the walls
Partition exterior walls protecting against the wind and the water aggresions but letting the humidity go through ; interior partition for the intimacy and the acoustic comfort
Shell metallic roof to recupy rainwater ; large gutters made of palmtree trunk ; coconut and palm fabric screens as wind and waves protection ; the floor can easily let the water flow outside in case of flooding
Roof
Exterior wall
Interior partition
Floor
steel sheets palmtree beam coconut fiber pandanus timber palmtree wood
palmtree wood palm sealing coconut fiber pandanus timber palmtree wood
coconut fabric coconut fiber pandanus timber coconut fabric
palm fabric palmtree wood coconut fiber pandanus timber palm fabric palmtree beam
1/10
1/10
1/10
A children room transversal section - 1/50
1/10
-- Floating Gardens -biological ecosystem
A LIVING CYCLE STRATEGY In the house unit lives a true sustainable ecosystem, with hens, fishes and plants interacting to nourish each other and producing enough food for the whole families. The fish and plant cultures are integrated in a specific aquaponic system. Aquaponics takes profit from the dejections of the fishes to feed the crops, and by doing so, clean the water for the fishes as their own dejections are toxic for them. The ammoniac in it is processed by bacteria into nitrites and then into nitrates, good nutrients for plants. To be effective, the system needs a regular water circulation.
The house production ecosystem
A TIDE-BASED AQUAPONIC SYSTEM To insure the water circulation (and its filtration), the floating gardens take profit from the tide movement. The two units (fishtank and planter) are connected and function like comunicating vases : the fishtank is conceived as a floating device, moving up and down with the tide. On the contrary, the planters are static, put on a structure planted on the ground. With the rising tide, the water full of diluted fishes dejections flows into the planters, where the ammoniac is processed into nitrates and consumed, cleaning the water. When the tide lowers down, the clean water flows back to the fish tank. The up and down water movement inside the planters is necessary for the plants as their roots need to be oxygenated regularly. Compared to a classic aquaponic system, the 6 hours delay induces a low flowrate that we can compensate by maintaining a lower fish density than normal. It also improves their well-being. On the contrary, the crops can be planted in high density as all the nutrients come directly and regularly to their roots through the water, thus preventing the competition between plants.
static floating
high tide
static floating
low tide
The tide-based water circulation
Planters lying on the static structure
Static structure planted on the seabed
The aquaponic system : low tide - section 1/100
Floating fishtank moving with the tides along the static structure The aquaponic system : high tide - section 1/100
ENVIRONMENTAL PROTECTIONS AND STRATEGY Strong tides The water level difference between the high and low tides is approximately 60 cm in this area, but can reach larger gap in case of strong tides. To prevent the flooding of the planters in this case, the floating structure is conceived so as to mecanically lift them when the water rises above a certain point, without interfering with the system operation. unusually high tide
usual high tide
usual low tide
The floating structure lifting the planters section - 1/35
Use of local and recycled ressources
Aquaponics work well with coconut material : coco shells are great mechanical filters as well as biological filters to help installing the beneficial bacteria, so they are used at the bottom of the planters, where the bacteria can colonize. Coconut fiber is ideal as media to make the plants grow in the planter, since it easily retains the nutrients and humidity, but keeps oxygenated. Once the media is over-used and full of organic residus, it can be used as an efficient compost for traditional soil-based cultures.
For the floating capacity, oil drums can be used and are sometimes found in the debris littering the island. Any plastic recipient can be transformed into plant receiver after a clean-up, as long as they are sealed.
Strong tide disposition section - 1/100
Wind and waves To prevent the agressions from the salty water coming in through waves and from the strong winds, the gardens are installed at the core of the project, so that the built part of the housing unit offers a protection, breaking the potentially high waves and deviating the wind during storms.
The protective shape of the building planymetry - 1/500
-- Water treatment -biological ecosystem With a precipitation rate of 2100mm/year, a 16 people housing unit can recupy up to 672 m3 with the roof surface. It represents 42m3 for every person, wich is more than needed for the human use.The rain water, once collected, is brought to 3 water columns : 2 for hygiene uses, and 1 bigger for the kitchen.
A water column is built from local ressources such as timber for the structure, fabric for the filtration, and earthworms and wood chips for the biological decomposition (lumbrifiltration) ; but also with imported materials like plastic tanks or metallic tanks to insure perfectly sealed containers. The water treatment system (6) is a process based on
The water column system 1
2 3
4
5 7
6
living components (bacterias and worms) and can treat grey and black water. The requirements to make it work correctly are the use of natural based products and the less detergents possible so as not to kill the living creatures. Once treated, the water is clean enough to be used as irrigation water, as it is filled with organic residus and nutrients. It can
1
rain recuperation
2
gutter leading to the water columns
3
mechanical filtration, with fabrics of different sizes
4
water storage tank
5
consumption and recollection
6
3 types of treatment : primary filtration, biological decomposition (lumbrifiltration) and decantation
7
water reused for the aquaponic system or for irrigation on traditionnal cultures
also be properly released into nature as it won’t participate to the eutrophication of the sea, being cleaned from nocive agents through the treatment process. The mud produced in the process has to be taken out every year and can be useful as a fertilizer for the floating gardens, but also for traditional cultures.