2010. Retrieved 1 July 2010. Cite web URL http://dictionary.reference.com/browse/duplex+house Title Duplex House Year of publication 2010 Website Dictionary.com Publisher Ask.com URL access date 1 July 2010 ↑ Merriam Webster Online: definition of fourplex ↑ ↑ Most Expensive Homes In The U.S. 2006.