EVEN THE MOST casual horror-movie viewers know that basements are where protagonists go to, as TikTok teens would say, “get unalived.” For interior designers, however, the most unnerving part of these spaces isn’t who (or what) might be hiding in wait, it’s often what’s lying in plain sight: their décor.

Too many homeowners treat basements “as a second-class space where old furniture and random junk goes to die,” complained Anelle Gandelman, founder of New York’s A-List Interiors. “A basement is not the place for appeasing...

EVEN THE MOST casual horror-movie viewers know that basements are where protagonists go to, as TikTok teens would say, “get unalived.” For interior designers, however, the most unnerving part of these spaces isn’t who (or what) might be hiding in wait, it’s often what’s lying in plain sight: their décor.

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Too many homeowners treat basements “as a second-class space where old furniture and random junk goes to die,” complained Anelle Gandelman, founder of New York’s A-List Interiors. “A basement is not the place for appeasing your husband with his ugly leather recliner,” echoed West Palm Beach, Fla., designer McCall Dulkys.

Here, architects and designers share five other frequently encountered below-ground blunders and suggest less-frightful alternatives.

ODD-SHAPED OPPORTUNITY In an Oyster Bay, N.Y., basement, interior designer William Cullum made a wonky space welcoming.

Photo: Don Freeman

1. The ‘All Things’ Space

New York designer Elizabeth Gill lives in fear of families who ask her to turn their cellars into an all-in-one combination gym, playroom, family room, man cave and mother-in-law suite. “Then, I get the stare and a ‘Can you make all that work?’” she said.

Instead: Prioritize. “Determine the most important use of the space and make that the focus,” said Ms. Gill. Any extra living area can be a bonus in a crowded home, she said, “but you ultimately will end up using a space that is functional and complete—not one cluttered with lots of things that detract from the original design.”

2. Fateful Ceiling

A common feature in basements, dropped ceilings suspend large tiles in a metal grid, thereby leaving room to conceal inset lighting, ducts and other mechanicals. But they shave height off a room, contributing to the dreaded cavelike feeling and threatening to behead your taller friends. Other misguided attempts to hide ductwork also bug design pros. Washington, D.C., designer Melissa Sanabria’s peeve is soffits whose bottoms have been painted to match the ceilings and sides to match the walls, creating a two-toned effect.

Instead: According to New York designer Robin Wilson, 8-inch-deep high-hat lights, which need dropped ceilings, are a fixture of the past. Use new, shallow-profile overhead LED lights. Conceal ductwork and pipes in a dropped bulkhead that appears designed and purposeful around the perimeter of a ceiling, advised Bethesda, Md., designer Tamara Gorodetzky. Where a soffit is unavoidable, “paint walls, ceiling and every side of the soffit the same color so everything disappears,” Ms. Sanabria said.

3. Pall-Casting

Leave the flickering fluorescents to “The Exorcist.” Basements are dark spaces, “and improper lighting creates uneven, shadowy areas,” said New York designer Rozit Arditi.

Instead: Even if you’re going for a moody man cave, “you need good lighting that can be fully illuminated and also dimmed for cozy ambience,” said Charlotte, N.C., designer Layton Campbell. Incorporate a mix of light sources such as floor lamps, table lamps and sconces so you needn’t depend on one overhead fixture, advised Ms. Arditi. Linear, ceiling-tracked LED lights can help lead the way from one space into the next, said Mary Maydan, an architect in Palo Alto, Calif., who installs them with a 90-degree bend as they flow from a hallway into an adjacent family room. “This creates continuity and makes the corridor act as an invitation into the next space.”

4. Neglected Nooks

Irregular areas of foundations are often covered over or turned into closets. “But especially in basements that are largely open, these odd and unusual shapes offer special moments for decoration,” said William Cullum, senior designer at Jayne Design Studio, in New York City.

Instead: Knocking down walls and rejiggering spaces is expensive, so get creative with what you have and use it as an opportunity to try something you’d never risk on the first floor, Mr. Cullum said. For one Oyster Bay, N.Y., basement (shown above), Mr. Cullum made a banquette that conforms to a polygonal footprint, established by the breakfast room above, and installed curtains on an existing steel beam, creating a special reading nook with a cozy, tented feel. “It’s a small retreat within an expansive space,” he said.

5. Wannabe Wood

Dark, dank 1970s-style paneling comes across as hopelessly dated and usually represents a “total departure from the rest of the house” said architect Margie Lavender, principal at New York City’s Ike Kligerman Barkley. Old-fashioned paneling is not moisture-resistant and can be a place where mold grows, added Ms. Wilson.

Instead: Ms. Wilson uses thin brick cladding or dry wall back with cement instead of paper—typically used in bathroom renovations—to prevent mold growth. Stick with light colors to maximize limited light, advised Ms. Lavender, and consider an accent wall of high-gloss tile, in cream or robin’s egg blue, to add texture and reflect light.

Notes From Underground

Strange basement décor

The first rule of avoiding a creepy basement? Get rid of those one-eyed antique dolls.

Illustration: Chris Lyons

“I got totally freaked out when I walked into a basement that housed an antique doll collection. Cue the scary horror music.” —Layton Campbell, designer, Charlotte, N.C.

“A full barbecue grill with a chimney at one end and a wood-burning fireplace on the opposite side. I can understand a man cave, but to have two fire-generating things in a basement could mean that your house burns down.” —Robin Wilson, designer, New York

“I was asked to help a client display his collection of medieval torture tools.” —Tracy Morris, designer, McLean, Va.

“Every wall was covered with PEZ candy dispensers. It was quite the collection.” —Sterling McDavid, designer, New York, N.Y.

“A toilet in the basement without any sort of enclosure.” —Luke Olson, senior associate, GTM Architects, Bethesda, Md.

“A potential client had a hot tub in the basement. It was odd and immediately felt like some weird castle dungeon with the smell of chlorine and mold.” —Miriam Verga, designer, Mimi & Hill Interiors, Westfield, N.J.