With more than 33 million square feet in the works, the Washington area accounts for a whopping one-third of the total commercial space under construction in the United States.

For developers and planners, mixed-use is very much in: Five of the 10 biggest construction projects blend more than one property type. Half of the developments on the list include an apartment or hotel.

While CityCenterDC has been nabbing headlines since it broke ground in 2012, few would expect that the mixed-use Neabsco Common in Prince William County would eclipse it. The suburban project certainly qualifies for a spot on the list of the region’s most ambitious projects, with two Hilton-branded hotels and two multifamily projects being built right now, for a total of 1.4 million square feet. Retail and offices are also planned. Meanwhile, with its ground-floor Safeway grocery, the Exchange at Wheaton is an example of the new wave of apartment development, where residential units stand above street-level store fronts.

Despite the popularity of multipurpose developments, single-use projects are well represented on the list of biggest construction projects, with the monstrous Marriott Marquis at No. 1. The massive convention center hotel on Massachusetts Avenue NW will add nearly 1,200 rooms of guest accommodations in downtown D.C. when its doors open in 2014.

In Northern Virginia, Vornado Realty Trust has re-imagined the aging Springfield Mall as a live-work-play concept renamed Springfield Town Center. Planned for a higher density mix of office and residential uses, the first phase will focus on the retail component with the redeveloped former mall space to be completed next year.

A couple of office projects round out the list. One in particular, Tysons Tower, ended 2012 on a very positive note. Developers Hines and Macerich found that their gamble on speculative office construction paid off when they signed a keynote tenant, Intelsat, for 188,000 square feet in the high-rise building.

Whether single or mixed, suburban or urban, these grand-in-scale and concept projects are reshaping the landscape and filling out the skyline. And, with such a broad array of big properties in the works, it is clear that the development community is still betting that newer is better in Washington.

Erica Champion is a senior real estate economist with CoStar Group in Washington.