AMHERST — A downtown mixed-use building under construction, to house Amherst College students starting next fall under an agreement between the college and the developer, is continuing to raise questions from residents and members of the Planning Board about whether it is in compliance with town zoning rules.

“If it looks like a dormitory, functions like a dormitory and is managed as a dormitory by Amherst College, then it is nothing but a dormitory. What else could it be?” reads a letter submitted to the Planning Board by downtown resident Ken Rosenthal in advance of its meeting on Nov. 6.

The 45-55 South Pleasant St. mixed-use building, approved by the board in April, is being developed by Amherst developer Barry Roberts in two phases, with the historic 45 South Pleasant St. building known as the Hastings Building featuring the street level retail spot for the Amherst College Store, and the upper two levels to be converted into apartments. Those apartments will then be connected to the 55 South Pleasant building, a new five-story construction with apartments on the upper four levels.

But it wasn’t until this fall that planners learned Roberts would be entering an agreement with the college to house 63 students in the 22 apartments, possibly for several years, as a way to free up space in both Cohan Dormitory, located off Spring Street, and Valentine Hall, the campus dining commons building on College Street expected to be mothballed in the coming years.

Planning Board member Karin Winter told her colleagues that legal clarity is needed on whether a college dormitory is allowed in the downtown commercial zoning district, as well as if there is a way town officials could convince college officials to use some portion of the building to house families of young professors and visiting faculty.

Winter said the board shouldn’t be guessing if the arrangement is legal under town bylaws, pointing out that student-exclusive housing is only allowed in the fraternity/sorority and educational zoning districts. “We can’t just let this slip without a legal decision, or at least the advice of it,” Winter said.

She suggested that allowing this could put the town at risk of having the University of Massachusetts undertake a similar project to bring a dormitory to downtown.

“We have a problem,” Winter said. “How are we going to protect ourselves, if we take away this protection that you can’t have a dormitory in an area that isn’t zoned for it? They can easily put a little commercial space in there and then have that.”

But Senior Planner Nate Malloy said the building commissioner has already ruled the building does meet the definition of a mixed-use property, as each apartment has its own bathroom and kitchen. Malloy said zoning doesn’t typically get into determining the occupancy, observing that if a company rents all units from the building owner and then leases to individuals, that is acceptable.

“It is hard to get into kind of regulating the end user,” Malloy said. And prohibiting students and defining the type of occupants would be unusual.

Planning Board Chairman Doug Marshall said the building is providing affordable housing through a $1.1 million cash payment to the town’s affordable housing trust, as well as property taxes and commercial space.

“My opinion is 45-55 was a project that went through the process exactly the way it should,” Marshall said. He said the hearings were legally advertised, and while he had hoped for a some variety in tenants, he knew it was possible this wouldn’t happen since the floor plans didn’t show apartments with master bedrooms and adjacent rooms for children.

“I feel like it doesn’t make sense to try to reopen that project and revisit that specific instance,” Marshall said.

Marshall said the project could be seen as a loophole, or more generous avenue, for housing.

“One thing I’ve wondered, is it a bad thing that suddenly the institution that those students actually attend now has some skin in the game in terms of where they are living?” Marshall said.

While the Planning Board in October voted narrowly not to reopen the public hearing for the 45-55 South Pleasant St. development, member Jesse Mager said one thing giving him pause is whether knowing there would be a single tenant could have changed the outcome. “Had that project come in with that presentation, I don’t think we would have approved it,” Mager said.

But member Fred Hartwell said having the store makes it a mixed-use project and that there is not a single tenant, even though Amherst College has an agreement with Roberts.

“It is a whole bunch of tenancies organized through, in this case, Amherst College,” Hartwell said.

He also noted that the board has been insistent that the town’s rental registration requirements continue to apply to the building.

Malloy said it might be a good time to examine all residential use classifications, including fraternity, sorority and social dormitory, all of which are related to Amherst and Hampshire colleges and UMass.

Malloy said his understanding is the project wasn’t developed to be student housing, but rather as a creative way to have a new mixed-use building downtown. “The intention of the application is really hard to get at,” Malloy said.

“From what I’ve heard is it was a private project that then was actually attractive to Amherst College,” Malloy said.