The West Tisbury zoning board of appeals on Wednesday unanimously agreed to allow well-known restaurateurs Mary and Jackson Kenworth to expand the footprint of the former Deon’s restaurant on State Road, approving plans for a new 2,170-square-foot year-round restaurant.

The board earlier this month cited a town bylaw which restricts commercial use in a residential zone to 2,000 square feet and expressed concern about the viability of the plan submitted by the Kenworths, who own and operate the popular Slice of Life Café in Oak Bluffs.

At issue was whether the board could legally allow a special permit; there was also a dispute over how the square footage of the building should be calculated.

The restaurant is a preexisting nonconforming structure dating back to the 1950s, before the advent of state building codes or town zoning bylaws. If the size of the restaurant is calculated using the basement area, it brings the total footprint to 2,153 square feet.

But because the basement has only bulkhead access and no windows, it violates the state building code, raising questions about whether the space could be used to calculate the size of the new restaurant. The board sought the advice of special legal counsel earlier this month.

In an opinion dated July 15, attorney Adam Costa said it was up to the board to decide how to calculate the maximum square footage. But he also wrote: “ . . . any increase in square footage beyond that currently existing, or if larger, permitted in the bylaw, requires a variance.”

Board members on Wednesday again debated whether they could calculate the square footage at 2,000 or 2,153 square feet. Chairman Eric Whitman said he understood why the Kenworths needed the extra space, but he questioned the logic of using an illegal space to calculate the size of the new structure.

“I don’t doubt that it’s been used for years as a basement, but nobody would argue that’s a legal space . . . this comes down to a building code issue,” he said.

The Kenworths over the past few weeks have been working with Island architect Chuck Sullivan to craft a new building plan under 2,000 square feet. On Wednesday they presented two plans, one with a building just under 2,000 square feet and one just over 2,150 square feet.

Mr. Sullivan said the larger plan was better both for the Kenworths and the neighborhood. The extra square footage will allow for a closed vestibule to be built in the front that would serve as a waiting area, which would keep noise inside the building and make the building more energy efficient. The larger plan also allows for better circulation and better access around the restaurant.

“It’s only 150 feet, but it makes a world of difference,” Mr. Sullivan said. “It would allow [Mr. and Mrs. Kenworth] to build the best restaurant for everyone.”

Board members were not entirely convinced until Eric Wodlinger, an attorney who represents the Kenworths and has also represented the Martha’s Vineyard Commission for years, argued the board is not bound to follow the state building code and may instead defer to the town zoning bylaws which allow for a larger building.

“In my opinion you are allowed to draw a distinction between the state building code and your own bylaw . . . essentially this is an opportunity for you to abide by your own law to provide a much better project,” Mr. Wodlinger said.

Mr. Whitman said Mr. Wodlinger made a convincing argument. But he had lingering doubts about the plan to expand the number of seats in the restaurant from 44 to 60.

“I am very much in favor of having a year-round restaurant in West Tisbury. I am just trying to find a way to make this work for the neighborhood. Is there a way to make this project work without so many seats?” he said.

Mr. Wodlinger said that over the years the restaurant has been permitted for more seats then what is currently being proposed. A hand-written sign, apparently prepared by representatives for the project, stated that Fat Tony’s had between 50 and 62 interior seats and 36 exterior seats.

The Wayside Restaurant had between 50 and 67 interior seats and 36 exterior seats, the sign indicated; the Roadhouse had 95 seats and the Red Cat had 66 seats. The most recent three restaurants in the location, the Ice House, Bittersweet and Deon’s all had close to 60 seats, the sign said.

Mr. Wodlinger suggested the seating issue was better addressed by the board of health, which administers the state sanitary code. “I think it’s a bit of a red herring for this board to go after the number of seats,” he said.

Several members of the public, some of whom were initially opposed to the plan, said the larger plan was clearly better for the neighborhood and urged the board to approve it.

“I think they have reworked this plan beautifully,” said State Road resident Mark Weiner, who was also a co-owner of the former Icehouse restaurant. “They are aware this is residential neighborhood and have taken steps to prevent some of the problems of the past. I welcome them to come to West Tisbury.”

Others pointed to the Kenworths’ reputation running both Slice of Life and previously the Sweet Life Café in Oak Bluffs.

“There is nobody better on this Island at running a restaurant. They are elegant restaurateurs and great people,” said Indian Hill Road resident Peter Farrelly. “There is no question this plan will be an improvement. It used to be you would pull in and you wouldn’t know where to drive or park . . . a lot of time I would end up in someone’s back yard,” he added.

“So that was you!” called out someone in the audience, drawing laughter.

Nearly all the public testimony was in favor of the larger plan.

Mr. Whitman noted that almost a dozen restaurants have come and gone at the site over a period of 50 years. He said he was excited about the prospect of a year-round restaurant staying in that location for a long time.

“The difference here is we have people who want to buy the property; people who have a vested interest in the property and what goes on there. For a long time we had people leasing the space who were trying to make the most amount of money during a very short season . . . I think [the Kenworths] will take better care of it,” he said.

The board initially voted to allow 2,146 square feet, but later amended it to 2,171 square feet to allow for an employee bathroom in the basement. The final vote was 5-0 in favor.

Following the vote, Mrs. Kenworth said she was happy the two sides could agree. “It really would have been no victory for us to get a plan approved that nobody liked . . . we are excited about coming to West Tisbury,” she said.