Sustainable and speedy: Prex Co. achieves construction goals with support from Leica iCON solutions

The Leica iCR70 robotic total station and Leica iCON build software support Prex Co. on their mission to build zero emission houses in Japan.


Headquartered in Kobe, Japan, Prex Co., Ltd. (Prex) is dedicated to low cost, short duration construction and environmentally friendly housing. As part of this mission, the company developed a unique precast foundation that has reduced foundation installation to just two hours.

The Leica iCR70 robotic total and Leica iCON build software for construction are integral components in Prex’s high-precision, fast installation of the precast foundation. This total solution enables Prex to achieve an extra short construction period – with only three days from the start of construction to topping out of the building and total projects completed in less than 30 days.

Dedication to innovative, sustainable housing

Prex is dedicated to attaining sustainable development goals, including offering zero-emission houses that reduce CO2 emissions to zero over the home’s life cycle, minimal houses that are compact and inexpensive and even off-grid housing that combines solar power generation and storage batteries for self-sufficient electricity. Prex’s methods are rooted in finding innovative ways to solve current challenges. For example, Japan's population has been declining for several years and, along with it, the working-age population. This has resulted in labour shortages for the construction industry. At the same time, Prex sees the need to develop more accessible and sustainable housing, helping people experience an increased standard of living, especially families. To address both these issues at once, Prex developed and now deploys precast foundations, which can be constructed in a short period of time with fewer workers at a low cost.

The precast foundation installation only takes two hours. Prex workers use a Leica iCON iCR70 robotic total station, which supports an easy one-person operation, for layout.

Precast foundations installed in just two hours

Prex’s precast foundation has revolutionised the construction process.

“Until now, building a foundation for a house required the skills of craftsmen, for earthworkers, rebar and formwork stages, and the construction period took about two weeks,” explains Prex’s Chairman, Shogo Arai. “However, with our originally developed precast foundation, it can be installed in just two hours without the need for specialists onsite."

The precast foundation developed by the company in 2019 is made in a factory and features high strength and quality, fabricated to millimetre precision. As a result, the precast foundation has a lifespan of about 150 years and can be used repeatedly.

For a building of about 70 square meters, the foundation work can be completed simply by installing the precast foundation at the four corners of the building and then stacking the factory-produced housing materials.

Before: Conventional on-site casting foundation method. This method requires many construction workers and about two weeks to assemble the formwork and reinforcing steel and to place the fresh concrete.

After: For a building of about 70 square meters, the precast foundation method only takes about two hours to install the foundation blocks at the four corners.

High accuracy and easy operation with a robotic total station

Since there is almost no need to cut and adjust the length of components on site, it is important that all layout accurately meets the design tolerances to ensure a perfect fit. For this reason, Prex carefully selected the construction equipment used for marking out sites. “The position of the precast foundation and the bolts installed in the foundation effect the accuracy of the entire house, so high accuracy within a tolerance of 1 millimetre is often required," says Arai. To achieve this high accuracy, Prex chose the Leica iCON iCR70 robotic total station with iCON build software – both designed especially for construction.

“We tested and compared many different types of total stations," reflects Arai on Prex’s decision to invest in the iCR70. “The iCR70 is very accurate, and even when a vehicle or worker crosses the road during the layout process and the total station loses sight of the prism, it recovers quickly. Our working environment is very dynamic and therefore we had to evaluate the ability of the total station to quickly recover from possible line-of-sight interruptions, keeping downtime to a minimum. We are very pleased with the performance of the iCR70 in this regard.”

“We also chose the iCR70 because it can be used both with and without a prism. We can use a prism when we need 1 millimetre-level accuracy and continue working efficiently with a non-reflective target when it is difficult to use a prism," says Arai. In addition, since both local grid and national coordinate systems can be used for marking out coordinates, they can be used according to the scale and purpose of the site. Importantly for Prex’s goal of fast and inexpensive construction, the iCR70 also allows a single person to perform layout work, increasing layout productivity by up to 80%. “Before, we used to measure the distance between precast foundations with a measuring tape and check the height with a level, which required two or three workers to layout. However, with the iCR70, we only need one person to do the layout," Arai continues.

Smooth guidance with construction-tailored software

In combination with the iCON total station, Prex uses Leica iCON build construction software on the Leica iCON CC80 controller tablet to digitise and streamline the layout process. Working with a 3D model of the building created in AutoCAD and saved in DXF format, the first step is to the load the DXF file and the points to be laid out into the field controller running iCON build.

The screen then displays a 3D model of the foundation and other parts of the building, the points to be laid out and the current position. iCON build provides easy-to-follow navigation to the desired point, so anyone can reach points quickly without making mistakes. Additionally, with the CC80’s 7-inch touchscreen, Prex crews can easily see the layout points and navigation even in direct sunlight. With clear visuals and intuitive features, one-person layout is easily and quickly completed, allowing the rest of the installation process to proceed.

Layout points and current position on the 3D model in Leica iCON build. The software provides easy-to-follow navigation in terms of direction and distance to the target point.

Today, thanks to the technology in Leica Geosystems iCON construction solutions, Prex is turning their business goals of sustainability and a better tomorrow for everyone into a reality, validating their corporate philosophy and mission.

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