A federal probe of tainted Chinese drywall has broadened because a small number of homeowners are reporting that American-made drywall is causing some of the same problems: a sickening, sulfurous stench and corroded pipes and wiring.

“We are not limited in the scope of our investigation to just Chinese drywall,” said Scott Wolfson, spokesman for the Consumer Products Safety Commission, which is conducting the largest investigation in its history after thousands of homeowners complained and filed lawsuits.

The vast majority of complaints still center on China-made gypsum board imported during the recent U.S. housing boom, when domestic building materials were in short supply. And the commission’s investigation is focused mainly on the imported drywall, Wolfson said.

Sporadic reports are surfacing from owners of homes built with American drywall, and the symptoms they report are similar to those reported with the Chinese drywall: a rotten-egg odor that makes occupants sick, corrosion of copper pipes, and ruined TVs and air conditioners.

“We’ve got a huge problem here, and we just need help,” said George Brincku, 48, who bought his southwest Florida house in 2004 and almost immediately began noticing the odd smell, the corrosion of wires and headaches.

When he saw reports about Chinese drywall, he assumed that was the problem with his house — until he called the contractor who installed it.

“I have all 100 percent American-made drywall,” Brincku said.

He sent samples to the Massachusetts Institute of Technology, which found that the wallboard from Brincku’s home contained 50 percent gypsum and 50 percent cellulose, an organic compound. Drywall should contain mostly gypsum.

Researchers do not know for certain what causes the chemical reactions, but an MIT scientist said the mixture of gypsum and cellulose in Brincku’s wallboard, combined with the humid atmosphere in Florida, was releasing sulfurous gases, causing corrosion of copper, brass and silver.

“The only solution is removal of the drywall,” Thomas Eagar, an MIT professor of materials engineering, wrote in his report. He did not return a call from The Associated Press.

Most of the drywall in Brincku’s home was made by Charlotte, N.C.-based National Gypsum, which said its own testing found the material from the house contained just 4 percent cellulose.

“We absolutely don’t know how you could make wallboard with 50 percent cellulose. It just simply would not hold together,” spokeswoman Nancy Spurlock said. “We have been producing wallboard for 85 years in the United States, and we have never had a problem” similar to the Chinese drywall complaints.

Although Brincku has not sued, several other lawsuits have now been filed against American drywall manufacturers, including National Gypsum and Atlanta-based Georgia-Pacific Corp.

Georgia-Pacific declined to comment on the litigation, but spokesman James Malone said the company had heard no such complaints until now.

Attorney Brian Warwick, who is suing Georgia-Pacific in federal court on behalf of two Florida homeowners, said his clients also heard the reports about Chinese drywall and assumed their homes were built with the imported materials.

He believes reports of tainted U.S. building materials will increase as homeowners realize the problem is not just with some Chinese wallboard.

“All the media keeps focusing on is China, China, China,” he said. “So how many people are just dismissing their claims because they see they don’t have Chinese drywall, and think they don’t have tainted drywall?”

Reports of tainted Chinese drywall began to surface last year, and homeowners who bought houses with the imported materials have filed hundreds of lawsuits against builders, suppliers and manufacturers.

In a report issued Monday, the Consumer Products Safety Commission said its studies found a “strong association” between the Chinese drywall and corrosion. The agency also said it found a possible link between health problems and high levels of hydrogen sulfide gas emitted from the wallboard, coupled with formaldehyde, which is commonly found in new houses.

The commission also recently made public a separate 44-home investigation into homeowner complaints, listed on its Web site as a probe into “imported drywall.” In fact, 10 of those homes had American drywall.

Still, complaints about U.S. drywall are greatly outnumbered by those regarding Chinese imports.

Of roughly 2,100 complaints received by the commission, about 25 involve homeowners who reported issues with American wallboard, Wolfson said. That is not enough data to make a determination.

A University of Florida study conducted for CBS News tested new samples of U.S. drywall, new samples of the Chinese material and Chinese wallboard from problem homes.

The scientists found that most of the new U.S. samples released sulfur fumes, but at a lower level than the Chinese product taken from homes. However, the study also found that some American product had higher emissions than some of the new Chinese material.

Spurlock, of National Gypsum, said the company was “quite puzzled” with the University of Florida study.

Some experts have suggested that some homes may have been built with a combination of Chinese and American drywall, but since not all of the wallboard imported from China was labeled, it’s impossible to tell what’s what. The only solution in that case would be for homeowners to tear the house down to the studs and test everything.

Another theory is that bad Chinese wallboard could be contaminating other materials in the house. The federal government is also looking into that.

Meanwhile, Brincku has moved out of his house and is now renting because the odor persists, and the electrical outlets are failing.

“You turn a switch on, and it all buzzes,” said Brincku, who struggles to make monthly rent and mortgage payments. “I don’t have any money left.”