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Some imported gypsum wallboard products have proved problematic recently, with issues of off-gassing.

Several incidents of gypsum wallboard making homeowners ill and damaging mechanical systems have been reported in British Columbia's Lower Mainland. The dozen or so instances are linked to far numerous cases in the United States where Chinese drywall is believed to be the culprit.

The building material, thought to have been imported to North America between 2001 and 2007 from China, has been linked with sulphur-like or rotten-egg odours that have resulted in allergy-like symptoms and nose bleeds amongst some homeowners.

The issue is believed to be related to presence of iron disulphide (FeS₂ pyrite), which can produce hydrogen sulphide (H₂S), carbonyl sulphide, sulphur dioxide (SO₂), and carbon disulphide (CS₂). These compounds can also corrode air-conditioning coils and other copper-bearing materials, causing them to need frequent replacement. Blackened, scorched wiring behind switch plates and wall plugs have also been repeatedly found.

The problems may be linked to improper storage of the drywall during shipment, according to Glenn Wood, PhD, CIH, ROH. A senior health and safety consultant in the Mississauga, Ont., office of consulting firm, Golder Associates Ltd., Wood told Construction Canada Online large quantities of Chinese drywall were reputedly kept on sea barges for months, while awaiting permission for importation to the United States. The material could then have developed higher-than-typical density and a higher propensity to off-gas sulphur compounds.

As drywall is usually made of gypsum (i.e. hydrated calcium sulphate), sulphur is one of the main components present in the sample. All drywall has sulphur in its elemental composition; therefore the odour is not explained by an analysis of the total sulphur content alone.

The extent of the indoor air quality (IAQ) issues related to this is still unclear. In the United States, the Environmental Protection Agency (EPA) is investigating the problem's severity. While exposure to sulphur compounds may cause irritation and breathing disorders, the level at which sulphur can be smelled (referred to as the 'odour threshold') is very low. In other words, an unfortunate or disagreeable stench does not mean one is being exposed to adverse, health-threatening amounts.

The situation reinforces the need for quality control and assurance when it comes to imported materials, said Wood.

"From a construction standpoint, materials ideally need to be tested," he continued. "However, such testing is onerous to do and in this case, the problem didn't manifest itself right away. It took a little while for this to develop."

"It's unfortunate China has another black mark—they're not the only ones who produce occasional lemons. Still, this should serve as a reminder you need to be careful of outside sources and that you need to be careful in verifying and keeping track of a product's source," Wood said.