Citra was founded with the objective of developing green buildings of higher quality, lower cost, and faster speed. As indicated by the McKinsey Global Institute report on the construction industry in 2017, a holistic approach must be followed to accomplish this: The building technology, the production technology, and information flow need to be rethought from the ground up in an integrated manner.
The advantages of higher quality and lower cost are apparent. Speed, however, has two major impacts: It increases customer satisfaction if their dream home is ready sooner, and it allows the same working capital to be used more frequently, increasing capital efficiency. In the long run, this reduces costs even further and increases the amount of homes built. For example, if a conventional home takes six months to build, while Citra can build it four to six times faster, the same working capital can produce four to six times more homes.
Citra’s approach combines Kaizen (continuous improvement) with dedicated in-house R&D and a strong network to universities and research institutes across the globe.
① At its core, Citra uses Expanded Polystyrene (EPS), which is a globally used insulation material with excellent ecological and technical properties. It is cheap and can be cut into any shape. Depending on the thermal insulation and statical requirements, the EPS sheets can be thicker or thinner, material density can be higher or lower, or Graphite Polystyrene (GPS, for example BASF Neopor) can be used instead of plain EPS.
② Chloride-free Magnesium-Oxide (MgO) rips are then inserted between the EPS sheets for two reasons. First, when a house including the roof is built from EPS-sheets and MgO rips, the rips keep everything in place. Second, the MgO rips connect the cementitious plaster that is later applied on both sides, creating a very strong composite structure. This provides high resilience to earthquakes and hurricanes, as well as high fire resistance.
③ Once the EPS-MgO structure is in place, the entire surface is sprayed with special high-performance cementitious plaster mixes, which are reinforced with high-strength chopped fibers. In standard structures, steel or glass fiber mesh is not required. The thickness of the plaster is determined by the structural requirements, such as building height and span width.
Where necessary for structural integrity, roofs and slabs are reinforced with basalt rebars placed directly underneath the MgO-rips. Basalt rebars are made from molten basalt stone that is embedded in an organic matrix. They have roughly twice the tensile strength of steel, require significantly less energy to produce than steel, are cheaper than steel, and do not degrade when exposed to alkaline conditions with oxygen. Therefore, thin plaster skins are possible in ceilings because no plaster coverage is required.
④ A waterproof layer with appropriate reflectivity is applied to the roof, keeping the plaster temperature below 80 degrees Celsius even under intense sunlight.
Up until now, Citra has constructed single-story and two-story homes with conventional slabs. Beginning in Q2 2024, the Citra Building Technology will support steel-free three-story structures.
Advantages of the Building Technology
The Citra Building Technology described above offers a number of outstanding benefits:
- Reduction of the ecological footprint: Grey energy is minimized by just using thermal insulation plus a minimum of plaster as required by statics. Operational energy is minimal due to excellent thermal insulation. Waste is reduced by a high lifespan, and finally the EPS can be recycled.
- Design freedom: EPS and MgO can be cut into any shape, and spray plaster application is fully flexible. This supports designs from ultra-low-cost tiny homes to fancy spacious villas, and allows Citra to develop a unique design language.
- Superior quality: In comparison to a conventional timber-frame home in the United States, a Citra home is more durable, does not rot, is highly resistant to hurricanes, and has better acoustic and thermal insulation. In comparison to a traditional brick-and-mortar home, Citra provides superior thermal insulation, which helps to avoid mold and cold spots.
- Lower cost: Using current production technology, a Citra home built without robots is 10-15% less expensive than a comparable conventional home. Once plaster robots and mobile EPS-factories are used, costs are expected to decrease by another 15% or more. Homeowners benefit from lower heating and cooling costs, lower maintenance costs, and an extended lifespan.
- Faster Construction: A full home can be constructed with EPS-MgO panels in a single day. Spray-plastering requires 2-3 working days, spread over two weeks. Citra currently builds homes in 6-8 weeks, and aims to reduce this to one month.
- Suitable for mobile automation and robots: Robots and mobile automation will play a major role in the future of construction, improving efficiency, reducing costs and material waste, and increasing quality. Citra has already begun developing a mobile EPS factory on trucks, and is collaborating with industry partners on plaster robots. These technologies will allow Citra to build high-quality, cost-effective structures in a fraction of the time it takes traditional methods.
- Thinner walls and roofs: In dense urban areas of Europe and North America, where thermal insulation is essential but living space is at a premium, the Citra technology can make walls thinner by 10-12 centimeters, resulting in a 3-5 percent increase in living space.
Citra is Agrément certified in South Africa and is currently in the process of being certified for the US market. All larger commercial banks in South Africa have approved the Citra Building Technology. Citra has filed for patent protection on key aspects of its technology and will actively seek to expand its patent portfolio.
Citra employs cutting-edge software for design and nesting to minimize production waste. EPS suppliers use CNC hot wire to cut EPS sheets from EPS blocks, while Citra uses CNC machines to cut MgO rips from large MgO panels. These components are then assembled in the Citra factory into larger panels, typically 1.8 by 2.5 meters, that include rebars and installed services as needed, but are not yet plastered.
Panels are transported to the construction site, where they are erected. Service installations are completed, depth gauges and corner beads are put in place, slab and roof rebars are spliced, and a thin layer of bonding plaster is sprayed onto the panels. Later, the main plaster layer is sprayed and finished.
Outlook for the Next Five Years
The following are prominent topics: the first practical application of plaster robots and the construction of mobile EPS-factories as a core component of mobile Citra Factories. A mobile EPS-factory is less of a technical challenge, but it is only economically viable if a minimum number of homes can be built per year.
Besides the above, Citra is looking into a number of smaller ongoing projects, including the use of more prefabricated components in the interior finish, fast foundation concepts, integrated photovoltaic and other energy-related improvements, and a number of practical work optimization aspects.
The goal is clear: better, cheaper, faster!
Throughout Citra, state of the art tools and data integration is considered a cornerstone. This applies to all key areas, from design to production to sales, from backoffice to construction site, from administration to engineering and optimization. While all key areas are already well supported, and a central Data Warehouse brings much of the data together, Citra aims to push the integration further, so that efficiency and speed are further improved.