What Type X actually is
Five eighths inch gypsum board with glass fibres distributed through the core. Under fire exposure, the gypsum releases chemically bound water which absorbs heat, and the glass fibres hold the weakened core together while that happens.
That combination buys time. It does not, on its own, constitute a rating.
Where the rating actually lives
In the tested assembly. A listing specifies every variable that was present during the test, and all of them contributed to the result.
- Board type and thickness
- Number of layers and how joints are staggered
- Stud material, gauge, and spacing
- Fastener type and spacing
- Joint treatment
- Whether insulation is required
- How penetrations are firestopped
Why penetrations fail assemblies
Fire and smoke follow the easiest path, and an unsealed pipe or conduit penetration is exactly that. It gives them a route straight through a wall otherwise rated for an hour.
Unsealed penetrations are the single most common reason rated assemblies fail inspection, and they are entirely preventable with an approved firestop system installed as the manufacturer specifies.
Where rated walls are usually required
Between an attached garage and the living space, corridors in commercial and multifamily buildings, stair and elevator shaft enclosures, demising walls between dwelling units, and around mechanical rooms.
Your local code and, on commercial projects, your drawings determine the specifics.
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