An office-to-residential conversion, the second major one to move forward on Market Street, is in the works at 785 Market, a.k.a. the Humboldt Bank Building, and the developer has plans to turn the building into 120 apartments for middle-income residents.

It's not clear how occupied, if at all, the 100,000-square-foot Humboldt Bank Building is. The building, constructed in 1906, has a Men's Wearhouse in its base and sits mid-block, with a 19-story tower — a skyscraper in its day — facing the street, and offices extending back to Stevenson Street.

As the Chronicle reports, Forge Development, which has recently completed a 240-unit residential project in the Tenderloin (TL Residences at 361 Turk/145 Leavenworth), is planning to purchase 785 Market Street and begin construction soon. Some of the 120 apartment units planned will be habitable by 2025, they say, and they've hired the same architect they used for the Tenderloin project, Gensler.

The building has especially sturdy bones — as the Chronicle notes, it was partially destroyed in the 1906 earthquake while it was under construction, and the builder proceeded to build it with the highest structural standards of the day.

Architect and developer Richard Hannum, the CEO of Forge, tells the Chronicle that the Humboldt Bank Building is "the poster child for conversions," and "exactly the right building" for this type of project.

And that is good. Because, as many have noted in the months since Mayor London Breed and others have been touting this notion of converting empty downtown office buildings into homes, a lot of old office towers are terrible candidates for conversions. Big floor plates with little plumbing and few windows don't make for easy flips into apartments or lofts.

Lucky for 785 Market, a whole side of the building that stretches into the block, away from the Market Street frontage, has windows facing an open plaza below (Yerba Buena Lane), and directly next door is a one-story retail structure, currently a Peet's Coffee, and a low-slung section of the Marriott Marquis complex that tops out around six stories.

This makes for multiple stories of residences with likely terrific downtown and Bay views, and not a lot obstructing those windows. And inside the top of the tower could probably make for some pretty rad, loft-type units.

It sounds like the the deal to purchase the property is not yet complete, but Forge sounds bullish about moving forward as soon as it is — and Breed's office is doing its best to get such projects through the approvals process quickly.

Like the TL Residences, Forge intends to keep rents at levels affordable to median-income earners.

The only other residential conversion that's already underway on Market Street is a few blocks up, in the Warfield Building. That project got underway last fall, and at least eight other buildings downtown are also on the docket to go from office to residential.