A key concern is the possibility that Congress, which appears to be moving toward overhauling the tax code this year, will alter or eliminate the mortgage interest deduction.
The NAHB has said that tampering with homeowners' ability to deduct their mortgage interest payments from their taxable income could dampen demand for housing.
Builders also see tighter mortgage-lending standards and problems with the home appraisal process as impediments to a full housing recovery.
Some of that uncertainty appears to have crept into the latest confidence survey.
The index tracking builders' outlook for sales over the next six months slipped 1 point to 49, the lowest level since August, when it was 43.
However, a measure of current sales conditions was unchanged at 51, though still at the highest level since April 2006. And a gauge of traffic by prospective buyers increased 1 point to 37, also the highest reading since April 2006.
Though new homes represent only a fraction of the housing market, they have an out-size impact on the economy. Each home built creates an average of three jobs for a year and generates about $90,000 in tax revenue, according to NAHB statistics.