Gypsum board is classified into multiple types under a single specification, and its fire resistance comes from a specific, well-studied chemical mechanism. This page covers that classification and what fire-exposure research shows about how that mechanism actually works.
What is it?
Gypsum is classified under ASTM C1396 across multiple board types: wallboard, predecorated board, backing board, water-resistant backing board, exterior soffit board, sheathing board, veneer base, lath, and ceiling board.
Why should I use it?
- A single specification classifies it across many building-board types — see “What is it?” above.
- Its fire-resistance mechanism has been directly measured and modeled, not just assumed — see Limitations for what that mechanism depends on.
How it’s used
In Construction & Building Materials, Gypsum is used across the board types classified under ASTM C1396.
Limitations — when it isn’t the right choice
- Fire-resistance duration depends on the specific board’s thickness and density — it isn’t a fixed property of “gypsum” in general. A 2007 peer-reviewed study exposed a 12 mm thick gypsum board (810 kg/m³ density) to the ISO 834 standard fire and measured a temperature plateau at around 100°C on the unexposed face. This plateau comes from an endothermic dehydration reaction between 150°C and 200°C that consumes heat as it releases chemically bound water — the main heat barrier mechanism, one that standard heat-conduction models fail to reproduce unless dehydration is explicitly accounted for. This was documented for one specific board thickness and density; it should not be assumed that every commercial gypsum board provides the same fire-resistance duration without checking its own rating.
