Thom Mayne of Morphosis in Los Angeles designed a house that would float if the city floods. James Timberlake of KieranTimberlake Associates in Philadelphia created a house with native vines climbing up the side walls to provide shade and coolness. Steven B. Bingler of Concordia in New Orleans envisioned a house with wide front steps ideal for a traditional crawfish boil.Those are three of the designs by 13 architecture firms commissioned by the actor Brad Pitt to help rebuild New Orleans’s impoverished Lower Ninth Ward, one of the neighborhoods hit hardest by Hurricane Katrina in 2005.The project, called Make It Right, calls for building 150 affordable, environmentally sound houses over the next two years. In a telephone interview from New Orleans, where he plans to present the designs today, Mr. Pitt said the residents of the neighborhood had been homeless long enough. “They’re coming up on their third Christmas,” he said. Mr. Pitt said he had been attached to New Orleans for more than a decade. “I’ve always had a fondness for this place — it’s like no other,” he said. “Seeing the frustration firsthand made me want to return the kindness this city has shown me.”Rather than bemoan the slow pace of redevelopment in the Ninth Ward, Mr. Pitt said he decided to address the problem directly by teaming with William McDonough, the green design expert; Graft, a Los Angeles architecture firm; and Cherokee, an investment firm based in Raleigh, N.C., that specializes in sustainable redevelopment. John Williams of New Orleans is the executive architect for the project. “If you have this blank slate and this great technology out there, what better test than low-income housing?” Mr. Pitt said. “It’s got to work at all levels to really be viable.”When Make It Right was announced at the meeting of the Clinton Global Initiative in September, Mr. Pitt pledged to match $5 million in contributions to the project, as did Steve Bing, the philanthropist. Nine other firms — all of whom donated their services — are involved, including Adjaye Associates; Billes Architecture; BNIM Architects; Constructs; Eskew & Dumez & Ripple; MVRDV; Pugh and Scarpa Architecture; Shigeru Ban Architects; and Trahan Architects. “We wanted to have a mixture of voices,” Mr. Pitt said. Beyond serving a public need, Mr. Pitt — who has a longstanding interest in architecture — was eager to see what the designers came up with. “I was most curious about advancing the discussion further,” he said. “That was certainly one of the benefits of this exercise. There is no other reason to call on these great minds if you’re just going to shackle them.”The green building elements will reduce upkeep costs by at least 75 percent, Mr. Pitt said, and reduce some of the problems that devastated the Lower Ninth Ward during Katrina, when multiple levee breaks forced thousands of people from their homes.The architects were each asked to design a 1,200-square-foot house for about $150,000, with Make It Right to help with the financing. The houses had to be built five to eight feet off the ground, with a front porch and three bedrooms.Mr. Mayne of Morphosis opted for a lightweight concrete foundation anchored by two pylons, like a pier, which would buoy the house if floodwaters rise. “It’s a boat,” Mr. Mayne said. “The population doesn’t want to live on stilts — and it’s expensive,” he added. “These are simple houses for low-income people.”Mr. Bingler of Concordia said his design called for homes “that would respond to the culture of the Lower Ninth Ward.” He said residents had asked him for “a house where the baby can be sleeping in the back, the mama making red beans in the kitchen and the grandpa can be on the front porch entertaining neighbors.”Mr. Pitt is asking foundations, corporations and individuals to contribute to the project by adopting one house, several houses or a portion of a house through the project Web site, makeitrightnola.org. “You can adopt a tankless water heater or a solar panel or a tree or a low-flush toilet,” Mr. Pitt said. “You can give it to someone for Christmas,” he said — instead of another sweater.Responding to critics who question the wisdom of rebuilding at all in an area likely to get hit again, Mr. Pitt said: “My first answer to that is, talk to the people who’ve lived there and have raised their kids there. People are needing to get back in their homes.”