The parking garage to be built south of the renovated Lawrence Public Library is shown in this architect’s rendering. The garage will hold 250 cars. Its design incorporates a space to hang banners.

Plans for extra taxes to pay for an extra level on a proposed downtown parking garage are going to take some extra study at Lawrence City Hall.

City commissioners at their Tuesday meeting kept alive the idea of spending $1 million to add 72 parking spaces to a garage planned as part of the $19 million library expansion project. But all five commissioners said they had concerns about how a special assessment would be added to the property tax bills of downtown property owners.

“I don’t see a lot of hard resistance to the idea that we need more parking downtown,” said Mayor Bob Schumm. “But I agree that in terms of how we assess the costs for this, there are some cases that aren’t as equitable as the whole.”

Commissioners expressed concerns after hearing from a crowd of about eight speakers largely opposed to the idea of adding a special assessment to downtown property tax bills to pay for the $1 million project. The assessment would be based on the square footage of the lot, which caused owners of several large pieces of property — including a representative of The World Company, which is the parent company for the Lawrence Journal-World and LJWorld.com — to question the plan.

Other property owners also questioned whether the general public should be asked to pay for more of the costs because the additional parking spaces likely will be used heavily by users of the Lawrence Public Library, the Douglas County Senior Center and the Lawrence Outdoor Aquatic Center, which are all public facilities located adjacent to the proposed garage.

“I think this really is more of a public parking thing,” said George Paley, who owns multiple buildings downtown.

Some residents argued the city should build only what was approved by voters in 2010 as part of the library project. But city officials have said adding an extra level of parking to the garage will never be cheaper than it will be during the upcoming expansion of the library.

“I feel like our job is not just to plan for the next couple of years but to really plan further out,” said City Commissioner Aron Cromwell. “We’re going to need those spots in the future. You can argue that we need them today, but we’re really going to need them in 15 years.”

Commissioners asked staff members to adjust the proposed special assessment financing plan to address several issues, including:

• A way to exempt from the assessment residential properties in downtown that provide their own parking

• A process to exempt from assessment the parking lots of commercial properties that provide significant off-street parking

• A policy that would allow churches and other tax-exempt organizations to not have to pay the special assessments

• A process that would make it easier for downtown property owners to file a protest petition to stop the special taxing district from proceeding

City Manager David Corliss said he would bring a new financing plan back to the commission in the next two to three weeks for consideration.