The fascinating facade of the 6 Star Green Star SA Office v1 design rated Nobelia building under construction in Kigali, Rwanda was an answer to a crossword puzzle that needed solving says architect Carlos Arroyo.

The towering mesh screen reduces the import of building materials, ensures the building is screened from the sun, and provides a visually appealing and pleasant facade.

The metal screen will stand about one metre from the main structure, leaving space for cleaning and maintenance. It is lightweight and can collapse to fit into a single shipping container. In Rwanda, building materials are scarce, and the desire on this project was to keep imports low as these increase the building’s cost and carbon footprint. The screen also lowers the requirement for expensive imported glass. The windows do not require any special profiling and will be encased in a wooden framework, which can all be locally manufactured.

Once established, the facade will conjure images of paradise. The plants growing along the facade (a combination of passion fruit vines, Lablab Purpureus, and Clerodendrum Splendens) will provide shade for occupants and bursts of beautiful seasonal blossoms, but could also produce food. The mesh facade provides a framework for the creepers to grow from locally made clay planters at each level.

Eloshan Naicker, sustainability consultant at WSP, the accredited professional on the project, says the facade is the most striking and holistic sustainability aspect of the project. “It’s like a human skin if it performs properly. It influences almost every aspect of the project, such as energy, water, materials and the indoor environmental quality of the building.”

“The temptation is to add gadgets to improve the sustainability, but we don’t believe in adding sophisticated, expensive gadgets and machines as remedial measures for basically unsustainable designs. Sustainability must be built in from the ground,” says Arroyo, and there is evidence of this throughout the Nobelia project.

“Integration, compatibility, inclusion, efficiency, sustainability, locality, cost control, environment, etc. All these words (and others) are the base of Carlos’ design rules and that makes the difference. We are forced to go further and find new results that can demonstrate what he believes in,” says BAC Engineering Consultancy’s structural engineer Xavier Aguiló i Aran.

From the ground up

Soil analysts assessed soil issues, such as retention to ensure minimal excavation and foundations, as this is a carbon-intensive part of the project.

After extensive lab testing, the cement requirement was reduced by one third through using a local source of fly-ash from volcanoes. It is often used for small-scale building in Rwanda, but required stringent lab analysis for a project of this magnitude. Habi, the client, did the sourcing and testing with support from the engineers and geotechnical analysts. “Habi is actively trying to create new local business opportunities, and such cement substitution addressed this priority,” says Arroyo, who commends Habi’s ethos on the project. “You don’t have an interesting project without an interesting client,” he adds.

The concrete requirement was further reduced through using hollow core slabs, which save on cement and circulate air at night. These are also locally manufactured.

Arroyo was determined to push the sustainability agenda, and Habi wanted certification as a reassurance they were delivering on their promises. Green Star was not in the brief from the start, although Habi always wanted an efficient, affordable building. Habi made a big effort for certification, even funding the country report on the viability of using the Green Star SA rating system in Rwanda, says Arroyo.

Producing the local context report meant checking credits could be measured against equivalent standards in Rwanda, or where there were no building standards or regulations, that South African standards could be used, explains Naicker. For example, there is no regulation in Rwanda on hazardous materials, so the South African Occupational Health and Safety standards were deemed to satisfy.

Natural ventilation

Arroyo says one of the highlights of the project was proving that one could build on the equator without resorting to air-conditioning.

The hollow core slabs encase two ventilation systems – one is night cooling, which pushes air from the top of the building, through the slabs and out to the street, to bring the whole structure to the night’s minimum low temperature without affecting the humidity of the interior. The other is the day air renewal, which works at low speed, and runs through the night-cooled structure. There are dehumidifiers on top of the building, working on an energy recovery loop, to control relative humidity – which is the key to achieving comfort in the tropics at minimum cost.

Finally, energy recovery ventilation (heat exchange) is used in the basement, where the showers and change-rooms are located and where stronger ventilation is needed. Before the cooler air is expelled from the building, it cools the air coming into the building.

Water wins

The building’s water use is expected to be an impressive 0.7litres/day/m2 and there is a triple water treatment system. City water is only used for water that people come into contact with for cooking, cleaning and basins. That water is then sent through to a greywater system where it is treated, cleaned and mixed with rainwater harvested for uses such as flushing toilets. Wastewater from there is then sent to a biodigester, or blackwater treatment plant, and water from there is purified and used for irrigation of the facade, which is done through a drip irrigation system.

Global team

The diverse nature of the project team added an element of ingenuity and energy to the project. With the client and contractors on the ground in Rwanda, architects and some engineers in Spain, Green Star AP in South Africa and QS and project management from Romania but on-site, the team had to ensure communication was handled well.

“With any project that aims to change the rules, you need to ensure everyone understands the goal. There are hundreds of people working on any project, and so this means many, many presentations and meetings and clarifications and interactions all the time. Sometimes people have good intentions to improve a project, or think that what is requested cannot be correct and so they will make mistakes. The intent needs to be clearly communicated over and over,” adds Arroyo.

Naicker says the highlight was definitely the rating announcement. Not only is it the first Green Star SA rating in Rwanda, it’s the first 6 Star rating outside of South Africa. “The amount of work was significant and there were many challenges so it was a relief when it came in,” he says.

“In twenty years I hope to see the building nicely matured like a beautiful garden. If we want to achieve a sustainable culture, we need to make it feel like a paradise. Sometimes sustainability is a bit grey, like we are not given many options – we try to make it better. We want it to be splendid and desirable. People must love the building,” concludes Arroyo.

By Christy van der Merwe

See earthworks Issue 31, April-May 2016 for the full feature.