Problematic drywall may not be a byproduct of solely Chinese manufacturing. In fact, some defective product may also come from American manufacturers, a new study indicates. The Consumer Product Safety Commission, in conjunction with Environmental Health & Engineering, recently released a report in which it tested 11 homes reportedly built with domestic drywall. According to the companies' findings, five homes showed results consistent with homes that contain problem drywall. Nine of the 11 properties showed electrical corrosion including blackened copper wire and air conditioning evaporator coils. The five homes with problematic drywall exhibited "corroborating evidence," such as sulfur build up, hydrogen sulfide emissions and copper sulfide development, synonymous with problem drywall. "The focus of this report was to evaluate homes reported to be constructed with domestically produced drywall," the CPSC report said. "EH&E concludes that five of the homes in this study have drywall that is consistent with problem drywall. The CPSC compared the homes in its most recent study to homes it previously surveyed. All homes were reported to have domestically produced drywall by the owners. Neither the CPSC nor EH&H independently confirmed the drywall was made in the United States. As of Jan. 7, there were 3,770 incidents reported of defective drywall, according to the CPSC. Florida has the most with 2,137 cases, followed by Louisiana with 704 cases and Alabama with 215. China is often the source of this questionable drywall. There are specific federal guidelines for dealing with problematic drywall on the remediation side. The Department of Housing and Urban Development released guidance with the CPSC in March. The National Association of Home Builders too released remediation directions to its members. Write to Christine Ricciardi. Follow her on Twitter @HWnewbieCR.