The final size of Tesla’s $5 Billion battery factory is growing. Originally announced to occupy up to 10 million square feet (930,000 square meters), the Gigafactory is now expected to reach 13.6 million square feet (1.3 million square meters), according to a senior Tesla executive talking to Fast Company. The new number is a 36% increase to the two-story structure’s planned size, and is the equivalent of adding the entire square-footage of One World Trade Center to the project.

Once finished, the new size appears to put the Gigafactory in contention for the largest building in the world by volume, a title currently held by the Boeing plant. It is expected, however, to fall ever-so-slightly short of that title given its known 71-foot (21.6-meter) height. The Gigafactory will be the largest building in the world by footprint (Tesla’s Fremont-based car factory currently holds second place), and the fourth largest building in the world by floor space.

Despite the enormous size of the original plan, the additional floor space comes at no surprise. Tesla executives have said on multiple occasions that one factory will not be enough to support growing global battery demand as electric vehicles and grid energy storage products become more affordable. Officially, since April, the Reno, Nevada site has been labeled “Gigafactory 1,” indicating more will be built. Expanding the first Gigafactory until there is little room to grow should, in theory, be less expensive than shifting that extra supply to a second site. Yet German Vice-Chancellor and Economy Minister Sigmar Gabriel recently confirmed being in talks with Tesla CEO Elon Musk about the possibility of building “Gigafactory 2” in Germany.

Though the Gigafactory is still years from completion, in October, production of Tesla’s Powerwall and Powerpack products moved to an automated assembly line at the factory, months ahead of schedule. Battery cell production is expected to begin next year. By 2020, the Gigafactory will reach full capacity and produce more lithium ion batteries annually than were produced worldwide in 2013.

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