SEA-TAC AIRPORT -- After years of record growth, the Seattle-Tacoma International Airport is moving forward with the first major construction project.

The expansion is aimed at addressing the breakneck speed that's made it the fastest growing large airport in the country two years running. Passenger growth amounted to 13 percent in 2015, and is still running at more than 10 percent, double earlier forecasts of 5 percent for 2016.

The nearly $550 million project called NorthSTAR will expand the current North Satellite by another 180,000 square feet. Much of that is to extend to the west another 240 feet adding another eight gates, bringing the total to 20. The rest will expand the current terminal with more restaurants and stores.

PHOTOS: Sea-Tac NorthSTAR project

The North Satellite is the current center of Alaska Airline's terminal operations at Sea-Tac. Alaska will contribute nearly $37 million to build a new Alaska board room for its best customers and spaces for employees.

The terminal hasn't seen any upgrades since it opened about 40 years ago. The complete renovation of existing spaces will move ceilings much higher, and go with much brighter paint and glass.

Other plans are to add in more seismic protection against earthquakes and more environmentally sustainable features, including the use of rainwater to help flush toilets.