Mayor Chris Coleman said Monday that reusing part of the vacant Gillette/Diamond Products factory for parking below St. Paul’s future Lowertown ballpark won’t work, for both cost and design reasons.

In a letter to Lowertown residents and businesses expressing concern about the downtown neighborhood’s parking issues, Coleman said that numerous studies and letters from consultants and engineers make it clear that the building’s preservation is “untenable” if the $54 million project is to move forward.

“Planning for a ballpark with capacity for thousands of fans with such a limited space makes our ability to maintain any part of the Diamond Products structure nearly impossible, certainly too costly, and compromises basic ballpark ‘best practice’ design fundamentals,” the mayor wrote.

He added that studies show that there is “ample existing parking” for Lowertown residents and ballpark visitors, and that he is working with a downtown parking lot owner to find replacement spots for Market House condo owners, who are losing their parking to the ballpark site.

A group of Lowertown residents and business owners is rallying around a plan to fit the ballpark into part of the factory to create 500 to 600 parking spaces on two levels below the field.

Council Member Dave Thune, who has urged Coleman to consider that plan, said Monday that the mayor gave “a fair response” but that possible reuse of the factory shouldn’t be dismissed.

“There’s a million ways to design anything, and to claim there’s only one possible design for the ballpark is kind of disingenuous. Anything can be looked at again,” he said.

Thune added that “the parking problem is going to cost somebody. I just don’t want it to be the people who live downtown.”

A fact sheet accompanying Coleman’s letter estimates that it would cost the project an additional $7.2 million to $16.2 million to incorporate part of the factory in the ballpark design, depending on whether it was adapted for light industry or commercial uses.

Coleman also says in his letter that reusing the building for underground parking would cost more than $12 million and that estimated parking revenues would fall short of paying for it. Thune said he’s awaiting an analysis on that point from parking operators.