"The Boring Company will be using dirt from tunnel digging to create bricks for low-cost housing," he wrote in a tweet about his nascent tunneling enterprise.

A company spokesman confirmed the plans, saying the bricks will come from the "excavated muck," and that "there will be an insane amount of bricks.” Musk has also suggested he has plans to sell them, and the company said future Boring Co. offices will be constructed from the company’s own bricks. 

How many affordable housing units those bricks will create, though, is a different matter, says Juan Matute, a lecturer at the University of California, Los Angeles, and associate director of UCLA's Institute of Transportation Studies.

Musk’s tweet "assumes that housing costs are driven by construction materials, and particularly, construction materials that can be replaced by bricks," Matutue said. "That's not the case." At least in California, the only state where Boring Co. has started digging a tunnel, land and labor drive prices more than anything else.

Going forward, a spokesman said, the company plans to make bricks out of excavated mud from all Boring Co. tunnels, not just the one currently under construction in Hawthorne, California, on land owned by Musk's Space Exploration Technologies Corp.

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When it comes to actual housing construction, bricks tend to be expensive, in part because assembling brick walls takes more work than other options, such as putting up panels. And because bricks don’t stand up well to earthquakes, a major concern in fault-riddled California, building codes typically require buttresses such as reinforced steel and rebar when bricks are used. 

On its website, Boring Co. says bricks could potentially also replace concrete in a portion of its tunnels' linings, which it says would help the environment as concrete production creates significant greenhouse gas emissions.

Musk seemed well aware of the possible risks in a separate plan for the tunneling byproduct that he tweeted out in March. Boring Co. could soon sell "life-size LEGO-like interlocking bricks made from tunneling rock that you can use to create sculptures and buildings," he wrote. "Rated for California seismic loads, so super strong." 

Another potential hurdle: Chemicals have contaminated much of the land under Los Angeles. Any contaminants showing up in the excavated Boring Co. soil would complicate efforts to make that material into bricks used for housing.

Challenges around the idea may not prevent Musk—who has a track record of delivering on projects that others dismiss—from getting it done, Matute said. 

"That doesn't mean the Boring Company can't buy some land and build a few low-cost houses, with a partner like Habitat for Humanity," Matute said. "And say, 'Look what we did.'"

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