You can set a calendar by the phone inquiries we receive at the Gypsum Association.

Spring brings numerous questions about flooded basements and the impact of the flood water on gypsum board, and early winter brings an influx of inquiries about semi-frozen joint treatment.

But we know that it is truly the summer season when the calls about the potential for exploding garages begin to roll in. And they come in every year, paraphrased as follows:

“I live in [Palm Springs/ Las Vegas/ Phoenix]. It is [109 F/43 C] today. I moved to the desert this past winter and I just parked my [Lexus/ Rolls/ Mercedes] in my attached garage today. I went on the Internet and reviewed your information about the heat exposure temperature of gypsum board, and I am very concerned that the heat of the car combined with the air temperature is going to cause the drywall in my garage to explode. What should I do?”

The polite response

At times like this, one is tempted to look for the smart guy answer and to advise the caller to sell the defective car; however, in representing the industry we generally opt for the polite response. And in this instance, that response is: “Do nothing.” Here’s why.

The language that the caller is referring to comes directly from GA-216, Application and Finishing of Gypsum Panel Products. Specifically, Section 1.4 states: “Gypsum panel products shall not be used where they will be exposed to sustained temperatures of more than 125 F (52 C) for extended periods of time.”

At first glance, that seems to be a fairly low temperature threshold since 125 F (52 C) is not an extreme temperature, and you can think of simple examples in everyday life where that threshold might be exceeded. But if you parse the language in Section 1.4 a bit, you quickly see that the restriction works quite well.

Gypsum contains about 21 percent chemically combined water, and in its natural dihydrate form (CaSO4


However, there are situations where the panel might be momentarily exposed to a temperature somewhat in excess of 125 F (52 C) for a short duration of time; and maybe that did happen in our garage example. In that instance, the language in Section 1.4 provides a significant level of flexibility for such an application when it includes the phrases “sustained temperature of more than 125 F (52 C)” and “for extended periods of time.”

Essentially, the language is making two points: First, a minor temperature spike of brief or short duration is not going to create a performance issue for the panels. Because the temperature of the installation area temporarily jumps above 125 F (52 C) does not mean that the entire neighborhood has been placed in jeopardy. Gypsum panels have a long history of successful use in such circumstances. A minor, short-duration temperature blip is not going to change that.

However, and this is the second point, the same language is also telling us not to install the panels in an area where the temperature will consistently be above 125 F (52 C) for a period of time that is other than a short duration. Such an application has the potential to create performance issues for the panels. Since gypsum can go through a chemical change when exposed to heat, deliberately exposing it to heat in circumstances where its performance may be placed in jeopardy is asking for trouble. In turn, this also means that a panel should not be installed in a situation where it will be exposed to an extreme temperature, say a temperature of 700 F, for even a short period of time.

In this specific instance, a car that is parked in the garage on a 109 F day likely is not radiating much heat and, if it is an attached garage, the garage is probably being cooled somewhat by the dwelling’s cooling system. So in reality, the actual temperature in the garage, even if the car was just shut off, is, in all probability, far below the 125 F (52 C) threshold.

Even if the temperature did spike slightly above the mandated threshold, it likely did so for a brief period of time. And, while it can get quite hot in the desert, opening the garage door to park the car is not going to create an exposure problem.

The installation criteria for gypsum panels have been proven out over many decades, and the 125 F (52 C) temperature exposure threshold has been shown to be a legitimate benchmark for an acceptable application. They should be complied with to ensure an acceptable application; however, they should be used with the latitude that the application language intentionally provides.