Hooray for tall buildings! A beautiful, 400-foot tower has been proposed for a corner on the north side of the Folsom and Spear intersection with a stunning, undulating design by Chicago architect Jeanne Gang.

Gang's Aqua Tower, completed in 2010, is already a standout piece of contemporary architecture in the Chicago skyline, rising 82 stories with a rippling series of white balconies across the glass facade. At half that height, the San Francisco tower would nonetheless be a striking addition to the Transbay district, with a twisting series of windows inspired in part by the bay windows of Timothy Pflueger's landmark 450 Sutter Street building, built in 1929.

Gang made a presentation this week along with developer Tishman Speyer to the citizen advisory commission for the Transbay district. Of course, because this is San Francisco, much of the discussion centered around the height of the building, and the rational for seeking an extra 100 feet beyond the 300 feet already zoned for the parcel. The developer will be seeking a height-limit exemption from the Planning Commission and Board of Supervisors.

This tower joins a couple of other notable pieces of tall architecture in the Transbay District, including a 550-foot tower proposed by Dutch architect Rem Koolhaas, and a 400-foot tower designed by Skidmore, Owings & Merrill.

In addition to Gang's design being better suited for a tall building — and perhaps one even taller than 400 feet — she and the developer pointed out that the increased land price from the extra 10 stories of market-rate condos would totally fund the 75 units of affordable housing, which was proposed for a shorter building on the same property. In total, 390 condominiums would be built on the property, split between the 40-story tower and an eight-story shorter building. 139 units, 75 of which will be in the shorter building, will be reserved for lower-income buyers.

As John King reports in the Chronicle, Gang said in her presentation, "What I like about tall buildings (aesthetically) is what you do with the height, the incremental moves along the way. It's not just the extrusion of a single form from bottom to top."

Gang is a graduate of the Harvard University Graduate School of Design, and she's taught architecture at Harvard, Yale, and Princeton. The 2011 book Reveal is about her studio's work, and their process.