Developers are eyeing this warehouse for artists in changing South Philly. The family who owns it isn’t ready to sell.

The painted brick warehouse that sprawls across the 1200 block of Carpenter Street is the kind of building that real estate investors dream about.

A nearly 17,500-square-foot lot. Plopped in the center of a fast-growing neighborhood. New, massive developments are sprouting up nearby. And large industrial buildings in the area provide endless real estate opportunities — space for new homes, retail, offices, and more.

But there’s just one thing stopping that dream: The owners aren’t looking to sell. Potential investors have walked in off the street, with bigger and bigger cash offers. No matter the price, however, the owners of 1241 Carpenter St. have the same answer: No.

“It’s understanding that word ‘enough,’ ” said Steve Krupnick, 69, the longtime owner of the building, which is located in Hawthorne, the small Philadelphia neighborhood that borders Bella Vista. “I don’t have aspirations to be a billionaire. I’m doing nicely, and I like helping people out.”

For the last two decades, the people that Krupnick likes to help have been an ever-growing cohort of Philadelphia artists who have flocked to his warehouse seeking space to carry out their work. The building was never supposed to be what it is today — four floors, brimming with artist studios. It became a creative haven by sheer accident: When Krupnick and his wife purchased the run-down building in 1997, previously owned by his father-in-law, he envisioned space for his own inventions business. Maybe a condo development. But when a colleague’s wife needed space for her art, everything changed.

“She asked, ‘Could I put an art studio up there?’ ” Krupnick said. “And I said, ‘Sure, what do you need?’ She said, 'Two walls, a door, a light switch?’ ”

Easy enough.

Since then, that makeshift studio has swelled into space for nearly 50 artists, who have carved out varying-sized headquarters. Some studios are small and humid, crowded with canvases, sculptures, and shelves. Others are airy, bright rooms that still display relics of the Main Belting Co., which occupied the building a century ago. Either way, all are similar in one way: Word of mouth got the artists into the building — and the affordable rents have allowed them to stay.

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Called 1241 Carpenter Studios, Krupnick’s building rents work spaces to artists for between $300 and $2,000 monthly, though most are available for between $400 and $700. Prices hardly change. There are times when tenants may be asked to contribute more for capital expenditures, such as the repair of a broken water heater, or a surprisingly high property tax bill. Otherwise, Krupnick said, rents stay stable.

"Generally speaking ... we don’t dramatically raise rents,” said David Krupnick, Steve’s 35-year-old son, who returned to Philadelphia to manage the building four years ago when his mother, Susie, became sick. “If you give someone a space to work, they want to know that they have enough [money for rent]. Not that it’s $300 this year, plus next year could be $375. It’s not, ‘Oh, hey, they built the Sprouts Farmers Market nearby, so now it’s $700.’ ”

“People want to know that they can be some place and that they can build a home there for their work,” said David, a former Morgan Stanley employee, who, upon returning to Philadelphia, worked out of 1241 Carpenter. There, he grew Webb Medical, a medical device business, and worked on other endeavors.

The reliability and fairness that 1241 Carpenter Studios portrays has attracted a wide-ranging group, many of whom came to the building years ago and have stuck around. The building doesn’t advertise space and vacancies are typically filled by referral. One artist, Patty Smith, a printmaker, book artist, and newcomer to the building, joked that it’s the “best-kept secret in Philadelphia.”

Still, 1241 Carpenter Studios has attracted artists such as Rasheen Waites, a 33-year-old self-taught designer from Hunting Park, who has built his business, Suede Square, from the basement. Waites, who moved his studio into the building six years ago, pays around $300 monthly — a price, he said, that has allowed him to focus, simply, on his art. The result: A boutique design company that specializes in evening wear. His small, clean studio brims with well-dressed mannequins and racks of couture clothes.

Then, there is the staff at Surface Print Source, launched by 33-year-old Melanie Palladinetti in her Philadelphia living room in 2012. She discovered 1241 Carpenter when visiting a friend. “I was like, ‘This building is amazing, I love the vibe and the community. How can I get in on a space like this?’ ” she said. Today, her company occupies a large, well-lit space on the third floor, where a lean staff of six creates fashion prints for brands, including Nike, Kohl’s, and Victoria’s Secret. Palladinetti’s rent is about $1,100 a month.

To be sure, 1241 Carpenter Studios is not Philadelphia’s only artist community — and the city has seen numerous new spaces pop up in recent years, even as others have folded. The Bok building, for example, once a public school, now exists with multiple uses, including artist studios, a wedding venue, and a bar. Jasper Studios, a renovated carpet mill in Kensington, offers studio space as well. So does Cherry Street Pier, the converted maritime warehouse located along the Delaware River.

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Such openings, however, have not been able to mask the frustration that the artist community has experienced with the closing of prominent spots, including the Philadelphia Sculpture Gym or the Snyderman-Works Gallery.

Still, local artists say, 1241 Carpenter remains one of Philadelphia’s long-lasting artist enclaves, and one of the best. The diverse group — a collection of painters, blacksmiths, book restorers, screen printers, and more — allows collaboration. If an artist needs photos for a project, they might hire Taylor Mosley, who works in the basement with Kyron Ryals in a photo studio called ‘The Gallery.' It isn’t uncommon for tenants to buy each other’s art. And they each take turns showcasing their pieces in the building’s exhibition room, Artspace 1241, which can be used for free monthlong rotations.

Part of the success, the artists say, is the result of the Krupnicks. It would have been easy for them to sell the property, now assessed at $1.25 million, as Steve Krupnick aged into retirement, winding down a successful career of inventing products, including the Flippy Flyer.

It would have been easy for them to sell when Steve’s wife, Susie, died after a long battle with breast cancer.

And it would have been easy for them to sell when investor interest peaked after developer Bart Blatstein purchased the massive lot at South Broad Street and Washington Avenue, just a block away.

Yet every time, the Krupnicks chose differently.

“I’m very happy, and we don’t need to do that to [our tenants],” Steve said.

David thinks similarly, too. “You have to understand: My mom’s face is on the front of this building in a mural,” he said. “There is a tremendous amount of money that it would require to let someone take that off the building.”