Robert LiMandri is stepping in as acting Buildings Department Commissioner after Patricia Lancaster handed in her resignation Tuesday.

The resignation was accepted by Mayor Michael Bloomberg, who Monday criticized the DOB's performance.

"I don't think anybody should be fully satisfied with the Department of Buildings' performance," he said yesterday. "Whether they've done everything they can is something I'm looking at."

However, since word of her resignation, the mayor has done nothing but lavish praise on Lancaster, speaking of how she rooted out corruption, and worked very hard to increase the number of inspectors.

"Patricia leaves a strong foundation of reform and improvement for her successors to build on," said Bloomberg in a statement. "And I thank her for her dedication to making New York City a far better place to live, work, and visit.”

Lancaster served as the agency's head for six years. She said that she is choosing to return to the private sector.

In a statement Tuesday, Lancaster said she was proud of her time in the position, including her work to update the 40-year-old building code.

"I am proud of the groundbreaking work the department has done during my tenure" she said.

Lancaster's resignation comes on the heels of a number of fatal construction accidents, including the recent crane collapse in Turtle Bay -- which killed seven. Several construction accidents have also occurred at the new Trump building in SoHo.

"And now with the resignation we have this opportunity to bring people of different expertise to a table and come up with rules and procedures, more inspections, better protocols, to ensure people's safety," said Manhattan Borough President Scott Stringer.

In the case of the Turtle Bay crane collapse, Lancaster testified the high-rise was approved in error, and Democratic Manhattan Assemblyman Jonathan Bing said after repeated requests, his office never provided construction plans.

"We may have been able to bring to the Building Department's attention some problems in terms of the plan and what was approved for this particular zoning," said Bing.

Thirteen people have died in construction accidents so far this year, one more than last year.

The mayor says that Lancaster's replacement has not yet been selected.