Problem Drywall From the 2000s

Why this matters

Between roughly 2001 and 2008, a quantity of imported drywall, most of it from China, went into American houses, heavily in the Gulf states and Florida during the post-hurricane rebuilding and in Virginia, among others. Some of it emitted reduced sulfur gases. The gas does nothing dramatic to the people in the house that anyone can see. It blackens copper, and it eats air conditioner evaporator coils until they leak.

That is why the person most likely to notice first is not an inspector or an electrician. It is the HVAC tech who is replacing a coil in a house that already had two replaced, and who has been treating each one as bad luck. A coil-failure pattern is a symptom of the house, not of the coils, and a tech who reads it that way saves the customer from paying for a fourth one.

What the gas does, and what you see

The emissions include hydrogen sulfide and other reduced sulfur compounds. Copper reacts with them to form copper sulfide, which is black and flaky, not the green or brown of ordinary copper oxidation.

• Evaporator coils: the copper tubes and return bends go dull black, sometimes sooty. Leaks appear and recur, often at the bends and in the tube sheet area. Replacement coils fail too, sometimes faster than the original did.
• Electrical: the bare copper equipment grounding conductors in device boxes and at equipment turn black, and the exposed copper at receptacle and switch terminals darkens. Insulated conductors stay bright under the insulation, so the black is at the exposed ends.
• Other copper and silver: blackened copper water pipe where it is exposed in a wall cavity, tarnished silver jewelry and flatware in drawers, faster than the owners expect.
• Odor: a sulfur or rotten-egg smell some occupants notice, often described as stronger with heat and humidity. Many homes with the problem had no obvious odor, so the absence of a smell does not clear a house.
• Appliances and electronics: repeated failures of electronics and appliance controls are reported in affected homes, though those fail for many reasons and are weak evidence alone.

Do not confuse it with formicary corrosion. Formicary (ant's-nest) corrosion also destroys evaporator coils, from organic acids such as formic and acetic acid off household products and building materials. It leaves pinhole leaks in tubes that otherwise look nearly normal. Black copper sulfide coating on every exposed copper surface in the house, wiring included, points to sulfur gas. A pinhole in a clean-looking tube with bright ground wires points to formicary corrosion. Each one has a different fix.

The federal identification guidance

The Consumer Product Safety Commission and HUD issued identification and remediation guidance in 2010, after a federal interagency investigation. It is guidance, not a regulation, but it is what inspectors, insurers and courts used to decide whether a house had it.

The identification approach has two stages:

• A threshold. New drywall installed, in new construction or a renovation, between 2001 and 2008, AND blackening of copper electrical wiring and/or air conditioner evaporator coils. A house that does not meet the threshold is not identified, whatever else is going on.
• Corroborating evidence. Items such as laboratory findings of elevated sulfur in drywall samples, markings on the drywall identifying a source associated with the problem, copper corrosion produced in a test chamber by drywall samples, and similar test results. The number of corroborating items required depends on the installation date in the guidance.

Read the current version of the CPSC guidance for the exact list and counts before quoting it to anyone; it was revised after it first issued. The remediation guidance that accompanied it called for removing the problem drywall and replacing the electrical distribution components (receptacles, switches and circuit breakers, though not necessarily the wiring), smoke and carbon monoxide alarms, gas service piping and fire sprinkler components, because the corrosion attacks the parts whose failure matters most.

None of that is HVAC work, and very little of it is any single trade's work. The tech's job is to see the threshold evidence and route it.

What you are allowed to look at, and how

Look only at copper you can already see or that your normal service exposes.

• The coil is in your scope already. Note the color of the tubes and bends, not just where it leaked.
• The equipment ground at the air handler or condenser disconnect is also in your scope, but it is inside an enclosure with line voltage in it. De-energize at the breaker, lock and tag it, and prove the conductors dead with a meter checked on a known live source before and after, per NFPA 70E Article 120 (120.5 in the 2021 edition, renumbered in 2024), with work practices at 29 CFR 1910.333(b)(2). Then look.
• The thermostat wire ends at the air handler's control board and at the thermostat base are low-voltage copper you already handle. Stripped ends that have gone black under the terminal screws are the same evidence as a black ground, in a place you can see with the system simply switched off at the thermostat and the air handler's power off before you touch the board.
• The outdoor unit is your control sample. The condenser coil and the copper at its service valves sit in outdoor air. If the indoor coil and indoor copper are black and the outdoor copper is ordinary brown oxidation, the source is inside the house. If both are equally dark, look harder at the outdoor environment (coastal salt air, a nearby industrial source) before you suspect the walls.
• Receptacle and switch boxes belong to an electrician. Do not pull devices to look. Ask the customer whether an electrician has ever mentioned black wiring, and recommend one look.

Worked example: the third coil

The case is from the peak years, which is when this pattern was first being read in the field. A house built in 2007 in a coastal Southern county. Its service record, assembled from the shop's history plus the owner's earlier invoices, read like this:

  SERVICE HISTORY - air handler, same location
  2007  system installed with house
  2009  evaporator coil leak, coil replaced (1)
  2010  evaporator coil leak, coil replaced (2)
  2011  evaporator coil leak - this visit
  notes, 2011 visit:
   - coil tubes and bends dull black, flaking
   - disconnect ground (proved dead) black
   - homeowner: silver tarnishes in weeks
   - no odor noticed by owner or tech

The intervals are the first clue. The original coil lasted 2 years, from 2007 to 2009. The first replacement lasted about 1 year, 2009 to 2010, and the second about 1 year, 2010 to 2011. A coil that fails at that pace, three times in about four years, is not a bad batch of coils; three different coils failed the same way in the same air, each faster than the one before it or as fast.

Now run it against the threshold. Drywall installed between 2001 and 2008: yes, 2007 new construction. Blackening of copper wiring and/or evaporator coils: both, on the coil and on the ground at the disconnect, seen with the circuit locked out and proved dead. The house meets the threshold for further evaluation. It does not yet meet the guidance's identification standard, because nobody has produced corroborating evidence, and the tech cannot produce it.

The call. The tech does not install a fourth coil as a routine repair. He tells the owner what he saw and what it may mean, writes it as "copper on evaporator coil and on equipment ground appears blackened, consistent with sulfide corrosion; house built 2007; third coil failure since 2009; recommend evaluation for problem drywall under CPSC/HUD identification guidance", and recommends an inspector who works to that guidance. If the owner needs cooling now, a replacement coil goes in with the owner told, in writing, that it is expected to fail the same way until the source is dealt with, and the shop's warranty terms say so.

What changes the answer:

• Clean ground conductors and a single pinhole leak point to formicary corrosion. That is a coil-material and indoor-chemistry question, not a drywall one.
• A house built in 1995 with a 2006 kitchen remodel can still meet the threshold, because the guidance counts drywall installed in a renovation. Ask what was remodeled and when.
• A house that was remediated should have documentation; ask for it before you assume either way.
• Time. Emissions are reported to decline as the board ages, so a never-remediated house today may show the record (black grounds, a coil history) more clearly than active symptoms. The threshold reads evidence of past exposure too.

The conversation

The owner has a real problem and a frightening word for it. Say what you saw, what it is consistent with and who confirms it. "I've replaced three coils here and the copper looks the same each time. That pattern can come from a type of drywall used in some houses built around then. I can't tell you it is that. An inspector who works to the federal guidance can, and it's worth knowing before you pay for another coil." See related: Telling a Customer About an Old Material Without Scaring or Understating.

Do not speculate about health effects, litigation or what the builder owes. Those are for the owner's doctor, inspector and attorney.

How to verify you got this right

• You read the coil history as a series, with dates, rather than one failure.
• You separated sulfide blackening from formicary pinholing on visible evidence, not on the leak alone.
• Any look inside a disconnect was done locked out and proved dead.
• Your record says "consistent with" and names the guidance, and does not say the house has problem drywall.

References

• See related: Recognize, Record, Route - the Rule for Legacy Materials; Dating a House by What You Find in It; How to Photograph and Record a Suspect Material
• U.S. Consumer Product Safety Commission and HUD, identification and remediation guidance for homes with problem drywall (2010, as revised)
• NFPA 70E Article 120 (120.5 in the 2021 edition, renumbered in 2024) (verifying absence of voltage); OSHA, 29 CFR 1910.333(b)(2)