Today’s stalled developments are unlike the blight long suffered by historic industrial boomtowns as a result of job loss and suburbanization. Our cities are experiencing a different kind of vacancy: stagnant sites of halted jumbo projects conceived during the real estate bubble. A far cry from the small razed-house lot (seen on the order of thousands in Detroit, Liverpool, Leipzig, and the like), today’s shelved sites often resemble lunar craters, spreading over entire city blocks.

The problem is pervasive. In Seattle, it prompted both The Seattle Times and a local real estate blog, Seattle Bubble, to create interactive maps where readers could post stalled developments in their neighborhoods; as of April, readers had identified 76 lots in the Seattle area. On the other coast, WNYC’s popular radio host Brian Lehrer posted an interactive “Halted Development” map online, in conjunction with an interview he conducted in October 2009 with New York State Assemblyman Hakeem Jeffries. Jeffries is spearheading a statewide effort to work with developers to refinance and convert their stalled projects to affordable housing as an alternative to foreclosure or mothballing.

The British real-estate publication Property Week has gone the furthest in terms of advocacy, launching the Site Life campaign to work with the real-estate industry and the public sector “to bring some life back into these sites through temporary uses … until development can start.” Partnering with two major developers, Land Securities Group and Westfield Group, as well as the British Property Federation, the campaign was endorsed by London Mayor Boris Johnson and city councils across the country.

Some of the campaign’s most notable successes are Land Securities’ quirky re-creation of a Jurassic forest in London—replete with 24 life-sized animatronic dinosaurs—which attracted 3,000 ticket-buying visitors in one week, and Westfield’s commitment to convert a 10-acre site in Bradford into a park. (The latter created a PR nightmare for the company just weeks before the April announcement of the park plan, when vandals pasted posters on the site proclaiming “Wastefield.”)

The trend is just now gaining traction in the United States. Lent Space in New York City, designed by Brooklyn-based Interboro, is one of the few examples of a temporary project realized with the cooperation of the site’s owner—in this case, Trinity Real Estate. Interboro principal Georgeen Theodore notes, “This project came out of the generosity of Trinity, but we wonder if there’s a way to provide incentives for developers to deal with this inventory of unused public space, looking perhaps at the model of Privately Owned Public Space (POPS), New York’s 1961 zoning ordinance that gave developers FAR bonuses for providing public amenities.”

The temporary use of privately or city-owned space is still feared, in part because the memory of an earlier generation of interventionists—for example, Liz Christy’s Green Guerrillas, who furtively lobbed “seed bombs” over fences in 1970s New York—remains fresh. When lot owners, including the city, later tried to wrest control of their properties, the communities that labored to improve them and thus add value to their neighborhoods were loathe to give them up.

“The term I use is the ‘People’s Park’ paradox,” says Michael Yarne of the San Francisco Mayor’s Office of Economic and Workforce Development, referring to the Berkeley park that political activists established on university-owned land in 1969, sparking a series of violent confrontations with the police and National Guard. “The risk is, if a private developer successfully creates a memorable space, he also creates a local constituency that loves it, and might be sowing the seeds for future opposition. He becomes the bad guy who wants to tear down a butterfly park.”

To encourage developers to take a chance, San Francisco is drafting what it calls a Green Development Agreement, which gives developers iron-clad protection for their developments, ensuring them the right to go forward with their already-approved projects, no matter how long it takes. In return, the city asks simply for a use that benefits the public. The entitlement process in San Francisco is especially cumbersome, requiring developers to renew on a one- to three-year basis, and projects are always at risk as entitlements are always subject to modification. In theory, the savings from not having to hire lawyers and architects to keep entitlements current could be applied to the cost of commissioning a temporary use.

Seattle, too, is developing legislation to provide flexibility to property owners of stalled constructions, “allowing for interim uses while owners wait for a turn in the market,” according to Bryan Stevens of Seattle’s Department of Planning and Development. “We are exploring the possibility of mobile vendors, retail, and space for public art, as well as standards for landscape and lighting.” The legislation was finalized in the spring and will be passed to the city council for approval this summer. Concurrently, the Seattle Design Commission launched a competition, Holding Patterns, to solicit interim uses.

With projects predicated on narrow windows of opportunity, timing is everything. Here are three good ideas that, fortunately, found the right time.

Lent Space, by Interboro, Canal Street, New York City
Opened in fall 2009, Lent Space is the fortunate offspring of a longstanding relationship between the Lower Manhattan Cultural Council (LMCC) and Trinity Real Estate, a major property owner. Trinity’s initial plan was simply to install sculpture on its recently cleared half-acre site, and it asked the LMCC to advise. The LMCC’s curator, Adam Kleinman, knew of Interboro’s winning scheme for a 2002 Dead Malls competition, so together, they developed the idea of a temporary art park.

Responding to the developer’s requirements to have the site closable at night, the designers installed along one length a decidedly parklike wooden fence comprising 8-foot-wide panels that pivot open, making a lively invitation to passersby to cross the space. The rotating panels have built-in benches on one side and face an open space where Kleinman is programming changing exhibitions of large sculpture.

The fleetingness of the project—projected to remain for three years—also drove the decision to create a tree nursery on site. “There are so few open spaces in the area, so we immediately wanted to have trees. But we didn’t want to plant anything if they were going to be torn out in a few years,” explains principal Daniel D’Oca. Working with the parks department and the New York Restoration Project, the designers devised movable planter boxes that grow trees that will wind up on the surrounding streets when Lent Space is over.

Pollinator Garden, 45 Lansing Street, and Tree Nursery, 399 Fremont Street, by Rebar, San Francisco
Last summer, the San Francisco Chronicle urban design writer John King dispatched a series of articles about the city’s stagnant construction sites, including at least a dozen in the South of Market (SOMA) district alone, challenging the city and developers to “breathe life into these voids.” The newspaper also invited local design teams to produce conceptual schemes for specific vacant lots, inspiring action on the part of at least two property owners: Turnberry Lansing, proprietor of 45 Lansing Street, and Fifield, which owns 399 Fremont Street. Both enlisted Rebar, a participant in the Chronicle’s ideas exercise, to enhance their sites in the short term.

At 45 Lansing, Rebar is creating a pollinator garden, a habitat for pollinating species such as honey bees, butterflies, beetles, and hummingbirds. “Urbanization has made it rough for pollinating animals and insects, so we thought we’d give them a food source,” explains principal Matthew Passmore. The site will be dotted with large circular planters, formed by straw wattles that are easy to install and sit lightly on the land, and packed with native wildflowers. The developer is paying for materials, but volunteers through the Pollinator Partnership are donating the labor.

At 399 Fremont, the designers take a page from Lent Space, installing a tree nursery in partnership with the Friends of the Urban Forest, which supplies street trees for San Francisco. Though still in its design phase (expected to be completed by fall), it will feature planter boxes for hundreds of trees that may be easily transported to another site when the time comes.

Proxy: Lots K and L, by envelope a+d, Octavia Boulevard, San Francisco
Architect Douglas Burnham, of Bay Area–firm Envelope A+D, stepped sideways into the role of developer to create an interim design for two lots in San Francisco. The city recently took control of several vacant lots along Octavia Boulevard and put them up to developer bid. Burnham assembled his own development team to bid on two adjacent lots, for which he had already designed residential buildings that won first place in the 2005 San Francisco Prize competition. His bid won, but then the housing market crashed.

In one of his meetings with the Mayor’s Office of Economic and Workforce Development last year, Burnham was asked to consider a temporary use for his or any of the other Octavia lots. “Our first thought was, ‘That’s intriguing; they’re asking us for free work,’ ” recalls Burnham. “But it got us hypothesizing about potential programs, like an outdoor cinema, pop-up shops, food stands, gardens, urban living rooms with movable furniture, and so on.”

He proposed a mixed-use intervention on two larger lots, around the corner from his own and closer to a commercial area, which the Mayor’s Office readily endorsed and ushered through zoning approval. Within a wrapper mostly of perforated mesh, filled in with tenting and scaffolding, Burnham proposes several discrete places for modified containers, open seating, courtyards, and more. “We want a mix of uses, but we don’t want it to look like a junkyard,” says Burnham, explaining their desire for an intervention that “really occupies the space, a volumetric ghosting of what a real building would be.”

He’s already lined up a pizzeria, a beer garden, and an ice cream stand, and hopes to create a temporary gallery space, “probably made out of panelized components that can be clipped together,” he says. With a three-year lease for one lot and four years for the other, Burnham must pay the city monthly what it was previously earning when the sites were parking lots; vendors are bearing the bulk of the cost of their own build-outs up front, in exchange for a low monthly rent.

“In many ways, the timeline is perfect, because three to four years is about the amount of time it takes for people to get tired of something,” quips Burnham. The project will be rolled out in phases, starting this summer.