Homebuilder confidence in the US dropped to a 17-month low in August, according to the National Association of Home Builders index. The index fell to 13, its worst reading since March 2009. Analysts had expected the index to rise to 15 from 14 in July. A reading above 50 indicates that builders view conditions as good rather than poor. The index has not climbed above 50 since April 2006. The NAHB data is the latest in a series of weaker readings for the US housing market.