Homebuilder sentiment unexpectedly fell for a third straight month in August to its lowest level in nearly 1-1/2 years, according to a survey on Monday that pointed to a weak housing market.

The National Association of Home Builders/Wells Fargo Housing Market Index slipped one point to 13, defying market expectations for a rise to 15.

A reading above 50 indicates that more builders view sales conditions as good than poor. The index has not been above 50 since April 2006.

The NAHB survey showed the current sales conditions gauge for single-family home sales slipped one point to 14 in August, the lowest level since June 2009. The sales expectations measure for the next six months fell three points to 18, the lowest level since March 2009.

The traffic of prospective buyers index was unchanged at 10.