On a recent afternoon in Hayes Valley, Bridger Harlington and Rachael DeVaux ordered food at Souvla before sitting on the Greek restaurant’s new parklet, feet from its front door.

Weather permitting, the parklet functions as an extension of Souvla’s dining room, lively in its own way and littered with metal trays of garlic fries and lamb sandwiches.

Harlington and DeVaux were visiting from Seattle, and Souvla was their first stop. The pair both agreed that the parklet is a smart business move, adding space for outdoor dining.

“I love it,” DeVaux said, right before Harlington added: “It’s something I always look for at a restaurant.”

Souvla spent four years and $90,000 to have the parklet constructed only feet from its door in Hayes Valley. Introduced in January, the parklet sprawls across four parking spots on Hayes Street and is capable of casting a shadow across the front doors of Souvla and its neighbor, Patxi’s Chicago Pizza.

Since the start of the program in San Francisco in 2010, more than 75 parklets have proliferated across the city, with similar initiatives now headed to Oakland, Berkeley, Miami, Los Angeles, Philadelphia, San Jose and even San Leandro. Yet questions are growing about the use of public space for the benefit of private businesses such as restaurants and cafes that can afford to build one to essentially expand their seating areas.

In the days after it opened, the new Hayes Street parklet garnered a brief protest from a nearby Hayes Street business, True Sake.

“A parklet for personal profit literally 30 feet from an actual park — perfect!” read a sign in True Sake’s window, referring to Octavia Boulevard’s social center, the 20-year-old Patricia’s Green public park, which is just steps from the new parklet. Below the board were sake bottles that bore the words “#SoSanFrancisco.” The sign has since been removed, and True Sake’s owners have declined further comment.

San Francisco requires parklets to make clear that they are public spaces and part of the city’s program. The design is also supposed to stand alone from the business, at least aesthetically. An example of this can be found at Ritual Coffee Roasters on Valencia Street, where the structure is made to look as though a wooden ship has washed up along the curb.

“There is signage on each parklet indicating that it’s part of the city program. By all accounts, it’s rather clear that they are for public use,” said San Francisco Planning Department spokeswoman Gina Simi. “There are no current plans to launch communications efforts to remind the public of that fact.”

Berkeley’s new parklet ordinance also requires the spaces have signage saying they are for public use. Still, it’s hard to determine how public it is. At a glance, the Cheese Board Collective’s parklet is a fenced-off space along Shattuck Avenue, often filled with folks who have made a purchase at the pizza spot. It functions as an extension of the dining room.

It’s hard to walk through any bustling San Francisco neighborhood without stumbling across a parklet. While GroundplaySF.org, a multiagency program of the city of San Francisco, has tracked more than 75 such spaces, there’s no official count of the parklets that have been funded by and opened next to food or drink businesses. But all it takes is a stroll down Valencia Street in San Francisco’s Mission District to uncover the trend.

In the blocks of Valencia Street between 18th and 24th Streets, parklets have opened at the Crepe House, Zaytoon Mediterranean, Ritual Coffee Roasters, the former Blue Fig Cafe (which is becoming a Señor Sisig outpost), Smitten Ice Cream and Dandelion Chocolate. A little farther down Valencia, just beyond 15th Street, is Four Barrel Coffee’s parklet. Hip in its thin, wooden design, the space is most often occupied by folks sipping coffee from Four Barrel.

As time passes and parklets become more synonymous with dining, the differentiation between the area being an extension of a restaurant and a true public space has to become more pronounced, experts say.

“Parklets have the potential to change the dynamics in a neighborhood,” said Robin Abad Ocubillo, an urban planner with the city’s Planning Department who previously oversaw the parklets program. Yet as as the parklet boom has grown, Abad Ocubillo said city officials were taking notice of who exactly was funding parklets in the city.

He admitted that from 2015 to 2018, there was a need for balance as food businesses came to open parklets in waves. He said efforts were made to increase diversity among sponsors.

“We wanted to have more non-restaurant and cafe sponsors. It was intentional,” Abad Ocubillo said, adding that the goal required working with nonprofits and youth organizations in the city.

Like every other parklet, Souvla’s project went through an extensive vetting process. It began around 2014 and seemingly encountered an endless stream of green lights from the community. Souvla CEO Charles Bililies said his team obtained more than 1,000 signatures of approval on a petition for the parklet project. Public notices were placed in the neighborhood by the city but never seemed to draw much attention. A public hearing was held at City Hall on the matter, and it didn’t seem to slow the progress.

“In our case, there was lively public debate, which is very much the purpose of these hearings. Ultimately, city officials ruled for the project to move forward,” Bililies said via email.

Despite True Sake’s sign, Planning Department and Public Works officials say they have not received complaints about the Hayes Street parklet.

There are standards to be met when it comes to implementation. San Francisco requires all parklets be built at least one parking space away from corners. The speed limit on the parklet street has to be 25 mph or less, and the parklets can’t “interfere with utility access, disabled parking, bus zones, or curbside drainage.” Even the furniture is encouraged by the city to be a mix of permanent and temporary seating that blends well with its surrounding area.

The costs to apply for, build and maintain parklets in San Francico can cost anywhere from a few thousand dollars to tens of thousands. It’s a hefty price tag for small food businesses like Venga Empanadas in the Mission, which opened its parklet in 2017.

Unlike Souvla, which took four years to open its parklet, Venga Empanadas co-owner Paula Capovilla said it took a little less than two years to create the bright orange seating area. The total cost? About $20,000.

“I’d say business has gone up about 20 percent since we got it,” Capovilla said, adding that the investment, which includes annual maintenance costs of around $500, was worth it. “Our customers just love it. It’s a public space, so it’s open to everyone, but it’s hard to imagine not having it.”

Justin Phillips is a San Francisco Chronicle staff writer. Email: jphillips@sfchronicle.com

Twitter: @JustMrPhillips