Microsoft is constructing two data centers in Northern Virginia partially using cross-laminated timber.

The data centers use a combination of wood, steel, and concrete, which Microsoft said is expected to reduce the facilities' embodied carbon footprint by 35 percent compared to conventional steel construction, and 65 percent compared to typical precast concrete.

DCD first reported on Microsoft's timber plans in August.

Cross-laminated timber, or CLT, is a fire-resistant prefabricated wood material commonly used as a building material around the world, but has not been widely used in the data center sector.

EcoDataCenter and Boden Type use CLT for their data centers in Sweden, as do some Icelandic data centers. Vertiv has also launched its own prefabricated wooden data center module.

Unlike EcoDataCenter, which was primarily built with wood, Microsoft's approach will mostly use wood as part of the flooring.

With CLT prefabricated offsite, it can be installed more quickly and safely than corrugated steel used in large commercial buildings, Microsoft structural engineer David Swanson argued. It can increase material costs by five to 10 percent compared to traditional timber, but it can be cost effective due to reduced construction time.

“We’re constantly trying to validate the suitability of these novel materials for use in a data center environment,” Swanson said. “We want to make sure that they’re going to perform, they’re going to be safe, they’re going to be resilient, and provide all the features that we’ve grown accustomed to all these hundreds of years that we’ve been using those other materials.”

Microsoft has pledged to be carbon negative by 2030, and remove the equivalent of all the carbon the company has emitted since its founding in 1975 by 2050.

While the company has reduced direct emissions by 6.3 percent over the past three years, indirect emissions have jumped 30.9 percent, partially due to its heavy data center buildout.

“It’s an all-hands-on-deck task,” Jim Hanna, sustainability lead for Microsoft’s data center engineering team, said of efforts to cut indirect emissions.

As part of that, contractors will be required to use low-carbon materials and equipment in data center construction, with contract language set to be updated.

“A lot of our suppliers are on the same journey as we are,” Richard Hage, head of global strategy for data center engineering at Microsoft, said. "[Everyone is] implementing key initiatives to lower the embodied carbon of their materials and their products.”

Alongside wood, Microsoft has also researched using earth, algae, and hemp in data center construction.

Microsoft and Amazon have invested in CarbonCure, which pumps CO2 into the concrete as it sets, and Compass Datacenters has used CarbonCure concrete in some of its buildings. Microsoft is currently using it in 'select' US data center construction.

However, this process only compensates for about five percent of the emissions from a given batch of concrete, and it is only possible to use it in a small fraction of the concrete being used.

Similarly, Microsoft has invested in Prometheus Materials, which uses microalgae to produce zero-carbon cement. The company said that it will trial a small amount of that cement in these two Virginia data centers.

It is also an investor in Sweden’s Stegra (formerly H2 Green Steel), which is building a green steel plant in northern Sweden that could reduce emissions by 95 percent, and Boston Metal, which has developed a process that generates oxygen instead of carbon dioxide when making steel.