Chinese Drywall: Sulfur Smell, Blackened Copper, and a Narrow Build Window

For a few years in the 2000s, especially roughly 2001 to 2009, some drywall imported from China off-gassed sulfur compounds. The gas corrodes copper. Air-conditioner evaporator coils blacken and fail, wiring darkens, and the house can smell like rotten eggs or struck matches. It was concentrated in houses built or renovated during the building boom in hot, humid states, Florida and the Gulf Coast above all, because that is where the imported board went when domestic board was short. It is not "any house with drywall from China," and it is not a 1970 ranch.

The window is narrow. The test is specific. The internet is not.

What it is

Drywall whose core produces corrosive gas in humid air. The CPSC and state health departments published identification guidance: production marks on the back of the board, the corrosion pattern, and the smell. Not every imported board from that decade is the bad board. Not every blackened coil is this drywall. A coil fails for ordinary reasons, including a simply old air conditioner. The pattern that fits this defect is corrosion in multiple places, copper and silver, plus the smell, plus the vintage and the region, confirmed by looking at the back of a sheet or by a lab that knows the protocol.

How to spot it in the listing

Region, build or gut-renovation year inside that window, and a history of repeated air-conditioner coil replacements. Remarks will not say "Chinese drywall" unless the house was remediated and the seller is using the clearance letter as a selling point. Ask for that letter if the year and place fit. Prior listings sometimes mention "new AC coil" more than once. Listing language will say the house is updated. The mechanical history says something else.

If the house is in Minnesota and was built in 1992, stop. This is not your defect. Spend the contingency on the roof.

How to spot it at the showing

Smell when you walk in, before candles. Look at exposed copper: the air-conditioner coil if a panel is off, copper pipes under sinks, the ground wire in outlets if you are allowed to look, mirror backing that is blackened at the edges. A single tarnished fixture is nothing. Black copper in several systems is the pattern. Do not rip a hole in the drywall at a showing. If the screen fits, an inspector or a specialist pulls one outlet or looks in the attic at the back of a sheet, where the plant name is printed.

The real risk

Repeat failure of copper components, a house that is hard to sell, and a remediation that means removing the drywall, the affected wiring and coils, and a lot of finishes. People lived through the litigation. Some houses were fixed under settlements. Some were painted and sold. A remediation without a clearance protocol is a story.

Insurance and lending

Carriers learned this claim the hard way and many excluded it or settled and moved on. Getting a normal policy today is often possible and still worth confirming in the affected regions if the house is the right age and has not been cleared. A documented remediation with photos and a contractor's affidavit is what underwriters ask for. Lenders follow the insurer and the appraiser. An obvious odor and corroded systems can become a repair condition. A cleared house with paperwork finances like any other house of its age. Do not hide the paperwork. It is an asset.

Typical cost ranges

Typical ranges, not quotes.

• Screening inspection when the year and region fit: often $300 to $800, more if samples go to a lab.
• Coil replacement alone, if you are only treating the symptom: often $1,500 to $4,000, and it will fail again if the board stays.
• Full remediation of an affected house, drywall removal through to clearance: commonly $20,000 to $100,000 or more depending on size and how much electrical and HVAC has to be replaced. This is the number that made the litigation. Get a scope that lists the square footage of board, the wiring, and the air handler, not a single scary figure with no lines.

Pass, negotiate, or investigate

Investigate only when the region and the construction year overlap the problem window, or the corrosion pattern is already in front of you. Do not test every house in the country for a defect with a short biography. Negotiate from a positive identification and a real remediation scope, or from a documented prior remediation you are willing to trust. Pass when the board is confirmed, the seller has no clearance, and the credit is a new coil and a coat of paint. Paint does not stop the gas. The inspection checklist can carry one line, "drywall origin if 2001–2009 Gulf Coast," and stay silent everywhere else.