Facebook has announced that it will build two new data centre facilities at its existing campus in Prineville, Oregon.

The company expects to invest hundreds of millions of dollars in the new buildings, adding to the already billion-dollar campus. Workers will break ground on the first of two new buildings before the end of 2017 and the facility is expected to begin serving traffic by 2020. The second facility will break ground next year and become operational in 2021.

The original Prineville data centre, opened in 2011, was Facebook’s first privately constructed, custom-built data centre. Since then, the campus has expanded to four separate buildings comprising more than 1.25 million square feet of usable space.

The two new buildings will have a total of 900,000 sq. feet of data centre space, with an additional 70,000 sq. feet of administrative space connecting the two facilities. The site was designed by Facebook to be energy efficient and currently operates with a power usage efficiency (PUE) of 1.06-1.08.

Facebook originally selected Prineville as the site for its first custom-built data centre in part due to the tax remediation offered by the local government. Existing tax deals have saved the company more than $70 million (approx. £52 million) to date, with $17.3 million in tax savings in 2016 alone.

The city of Prineville has confirmed that a property tax exemption deal for the two new facilities has already been signed. The new tax breaks will be offset by a $250,000 annual fee to be paid to local government.

The Facebook data centres in Prineville, along with a similar campus owned and operated by Apple, are credited with boosting the local economy. Along with jobs and housing benefits, Prineville receives approximately $600,000 per year in franchise fees from data centre electricity use.

Facebook’s facility in Prineville was originally criticized for purchasing electricity from a provider that uses fossil fuels. Facebook is said to be working on a renewable energy solution to power the new facilities under the state’s direct access program.