Residents at a pricey Brooklyn condo building claim the developer is refusing to fix their drafty, leaking units — forcing them to wear hats and coats indoors while battling black mold, a lawsuit charges.

The six-floor, six-unit building at 48 Box St. looks like a shining gem on an otherwise gritty Greenpoint block, boasting apartments that feature marble countertops, stainless-steel appliances, gorgeous wood flooring and in-unit laundry.

But residents — who plunked down $600,000 to $1 million for their units in 2013 — say in the Brooklyn Supreme Court suit that the building is a damp, mold-filled disaster that is freezing cold in the winter because of shoddily installed windows and a lack of insulation.

“It’s hard to feel comfortable in your own home after three years when, in the wintertime, you have to wear a winter coat and scarf and go to bed in fleeces and layer up the blankets because the building is just leaking air and the cold air is seeping in,” griped one owner, who declined to give her name.

Another owner said her three-bedroom apartment dips to as low as 30 degrees on the coldest days, and she has three children living with her.

“It’s kind of ridiculous to have to bundle up your kids before we go to sleep,” said the mom, who also didn’t want to be identified.

Residents in the building blame the leaks on lack of waterproofing.

They say the mold has spread beyond their units, including the ceiling of a shared gym in the basement.

The owners say they have lodged complaints with developers HM Ventures Group LLC and ASH NYC but that little has been done to fix the problems after three years.

The building’s board of managers is currently fighting in Brooklyn Supreme Court with the developers and architect Jung Wor Chin after suing for breach of contract, fraud and professional malpractice in May.

In court papers, the developers say they purchased the “substantially completed” building in 2011 and filed suit against Chin and others.

“If those conditions exist, which we do not believe they do, we’re not the cause of those conditions,” said Ryan Miller, a lawyer for HM Ventures and ASH.

A lawyer for Chin didn’t return a message seeking comment.