U.S. Sen. Mark Warner sent a letter Tuesday admonishing a federal agency for delays and missed deadlines in its investigation of the impact of Chinese-made drywall.

The Consumer Product Safety Commission, which Warner in May urged to move more quickly to determine if the drywall poses a health risk to homeowners, was set to finish indoor air sampling of homes and complete a preliminary risk assessment by mid-September.

The commission now expects to finish the indoor air sampling next month.

"My constituents have had their lives turned upside down by Chinese drywall," Warner wrote in the letter to Inez Tenenbaum, the commission's chairwoman. "Most have moved out of their homes and several are facing the prospect of having to foreclose on their homes. They need the schedule of these test results in a concise, easy-to-read manner so they will understand what lies ahead."

The wallboard has been the focus of complaints in several states, including Virginia. Homeowners say it emits a corrosive gas that damages household electrical systems and causes respiratory illness.

At least 150,000 sheets of Chinese-made drywall were imported by a local construction supplier. That's enough to build more than 300 homes. The drywall since has been found in housing developments in Norfolk, Virginia Beach, Newport News, Chesapeake, Williamsburg and northeastern North Carolina.

Several lawsuits involving the drywall have been initiated locally, including one by five home-owners filed in U.S. District Court in Norfolk.

"We realize how serious this issue has been and continues to be for many families in Virginia," said Scott Wolfson, a commission spokesman, in an interview responding to Warner's letter. "We are doing additional in-depth investigations. It's not a general slowdown. It's that our investigation keeps getting bigger."