U.S. homebuilders are feeling less optimistic about their sales prospects, reflecting concerns that rebuilding efforts following hurricanes Harvey and Irma will drive up costs for construction labor and materials.

The National Association of Home Builders/Wells Fargo builder sentiment index released Monday slipped to 64 this month. That's down three points from a downwardly revised reading of 67 in August.

Readings above 50 indicate more builders view sales conditions as good rather than poor. The index has been above 60 since September last year.

The latest index fell short of analyst predictions, which called for a reading of 67, according to FactSet.

Readings gauging builders' view of sales now and over the next six months declined from last month. A measure of traffic by prospective buyers also fell.