A model of the San Francisco Museum of Modern Art's planned expansion, seen on a recent visit by A.i.A. to the New York offices of the architecture firm Snohetta, resembles a cruise ship docked amid slender high-rises.

But the apparent heft of the structure is deceptive, and its horizontality is intended to embrace the surrounding area rather than obstruct. At street level and on the first floor, the design significantly opens up the museum, blowing through the back wall of the 1995 Mario Botta-designed building to allow more light into the oppressive lobby.  Snohetta principal Craig Dykers explained to A.i.A. how sliced-away sections along the building's roofline will provide views of neighboring buildings, as will additional rooftop terraces.




The 225,000-square-foot expansion, which rises 50 feet above the existing building, will double the museum's exhibition and education space. SFMOMA has so far raised $250 million toward the $480-million project, which includes $100 million for the endowment. The museum will close once construction begins, and will partner with institutions throughout the city to present exhibitions and programming. The expansion is scheduled for completion in 2016.

From the existing entrance on 3rd Street, visitors will ascend to the second floor, where admissions will be located. A promenade will allow the public to pass through the museum's lobby and see works without having to pay for access. A Richard Serra installation, for example, will be visible from a second-floor overpass.




Through the creation of an additional facade and a public promenade on the adjacent Howard Street, the plan connects the museum to Natoma Street, a small lane that currently dead-ends behind it. Director Neal Benezra noted that small shops and restaurants have recently opened on this and similar narrow streets that are tucked in between major thoroughfares. Instead of the encountering the Botta building's hulking back, visitors and pedestrians will be able to pass through and around the museum. Natoma will also connect SFMOMA and the city's planned Transbay Transit Center, under construction two blocks to the east.

The SFMOMA expansion has long been anticipated. Even before the museum struck a partnership deal in 2009 to house the coveted Fisher Collection of over 1,100 works, SFMOMA was outgrowing its Botta building. It constructed a rooftop sculpture garden in 2009 by buying the roof rights to a nearby building and connecting it to the museum. Since 1995, the collection has doubled to 27,000 pieces and annual attendance has more than tripled, to about 700,000.