The nation's homebuilders are taking a step back from their tax cut euphoria and starting the year on a slightly less sanguine note.

Builder sentiment fell 2 points to 72 in January, according to a monthly survey from the National Association of Home Builders called the housing market index. The downward move comes after the measurement hit an 18-year high in December, following the passage of the Republican tax cut plan.

Any reading above 50 is considered positive sentiment. The index stood at 67 in January 2017.

"Builders are confident that changes to the tax code will promote the small business sector and boost broader economic growth," said NAHB Chairman Randy Noel, a homebuilder from LaPlace, Louisiana. "Our members are excited about the year ahead, even as they continue to face building material price increases and shortages of labor and lots."

Builders rank those costs at the top of their list of problems faced in 2017, and the vast majority of them expect both to get worse in 2018, according to another NAHB survey.