The fix for leaky roofs at the Minneapolis Convention Center comes down to one word: plastic.

Convention Center officials, hoping to stop asphalt and water oozing from the center's iconic domes into the exhibit halls, are preparing to replace the copper with polyvinyl chloride (PVC). The leaks got some unfortunate attention this month when asphalt resembling "black goo" dropped onto a car at the Twin Cities Auto Show, one of 450 events at the facility each year.

Though not quite high enough to be part of Minneapolis' skyline, the Convention Center's four domes loom over the southern gateway to downtown.

Convention Center executive director Jeff Johnson said that after renovations, the three 23-year-old domes will probably look exactly the same. The fourth was built in 2001 and isn't being replaced.

"We've tried to stay true to what the architect put forward," Johnson said.

The plan is not fancy, but it's the cheaper alternative. A consultant estimated last week that replacing the domes with copper would cost about $15 million, and using another kind of metal would cost $8 million. The PVC option? Only $5 million.

"I think this is the most efficient, best use of this money to get a roof that is watertight and lasts for many, many years," Johnson said.

The consultants that recommended the PVC, Roof Spec Inc. of St. Paul, have also had a hand in renovations at the Basilica of St. Mary and the Cathedral of St. Paul, both of which have copper domes.

The existing Convention Center copper domes shed water but are not waterproof. That job is handled by the underlying asphalt, which is wearing out.

Johnson said the city-owned Convention Center spends several hundred thousand dollars a year making short-term repairs to the roofs, but "we've started to get more leaks than we want."

The new PVC roofs should keep rain and snow out of the Convention Center for at least 20 years.

Johnson expects to put the project out for bids later this week and start construction in June. If everything falls into place, the work could be complete by the end of the 2012 construction season.

Council Member Betsy Hodges, who leads the council's budget committee, said she hasn't polled her colleagues on the matter. It will come before her committee in the next several weeks.

"In the ideal world you use the resources you've got as best you can," Hodges said. "And I think we're looking at doing that here."

Council President Barb Johnson said it's not just the cost that makes PVC appealing.

"It's going to last longer than if we replace the copper with copper," Johnson said. "So as long as the look is maintained, I think people are pretty comfortable with that."

Eric Roper • 612-673-1732 Twitter: @StribRoper