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What Type X and Type C drywall are, how fire-rated assemblies work, and where San Antonio buildings typically need rated walls and ceilings.
By SCCI Drywall. Published 2026-10-22.
Fire-rated drywall shows up in nearly every commercial building and in specific parts of most homes. But "fire-rated" is one of the most misunderstood terms in construction. Here's a plain-language look at what it means, how Type X and Type C differ, and why installation details matter.
Gypsum naturally contains chemically bound water. When drywall is exposed to fire, that water is slowly released as steam, which keeps the back side of the panel cooler for a period of time. Regular drywall already does this. Fire-rated board improves it by keeping the panel intact longer once the gypsum starts breaking down.
Type X is the most common fire-rated board. It's typically 5/8 inch thick, with glass fibers mixed into the core so the panel holds together under heat instead of cracking apart and falling away. In tested wall and ceiling designs, Type X is the standard choice for one-hour fire-resistance ratings, and it's used in multiple layers to reach higher ratings.
You'll find Type X in corridors, tenant separation walls, stair enclosures, mechanical rooms and, in homes, on the walls and ceilings between an attached garage and living space.
Type C is an enhanced fire-rated board. Its core contains more glass fiber than Type X, along with additives such as vermiculite that expand under heat to help offset shrinkage of the gypsum. That extra stability makes it a common choice in ceiling assemblies, shaft walls and designs aiming for longer ratings. Some tested assemblies specify Type C by name, and substituting Type X in those designs isn't allowed.
This is the most important point: a panel by itself doesn't have an hourly rating. The rating comes from a complete assembly that was built and tested in a lab, then published as a listed design. Each design specifies:
If the installed wall doesn't match the listed design, the rating can't be relied on. That's why rated work needs a crew that reads the design and follows it, not one that "builds it the way we always do."
Every pipe, conduit, duct and electrical box that passes through a rated wall creates a potential path for fire and smoke. Those openings have to be sealed with tested firestop systems. Joints between panels are taped and finished, and the head of the wall, where it meets the deck above, often needs a rated joint system as well.
Texas doesn't use one statewide building code for every project. Cities like San Antonio adopt editions of the International Building Code and International Residential Code, sometimes with local amendments. Common places where rated construction is required include:
The project's architect and the local building official decide which walls are rated. The drywall contractor's job is to build those walls exactly to the approved design.
SCCI Drywall installs fire-rated wall and ceiling assemblies for commercial and residential projects across San Antonio and South Texas. Have drawings ready? Call (210) 875-0280 or request a quote.
No. Only board labeled Type X, Type C or another rated type qualifies, and even then the rating comes from the complete tested assembly.
Type C has more glass fiber and additives such as vermiculite in its core, which helps it stay stable longer under heat. Some tested designs require Type C specifically.
In many cases, yes. The garage-to-house separation is the most common example, along with certain ceilings and walls depending on the home's layout and local code.
SCCI Drywall serves San Antonio and all of South Texas with drywall installation, drywall repair, remodeling, metal stud framing, light gauge framing and acoustical grid ceiling systems for residential and commercial projects.
Phone: (210) 875-0280
Email: sccidrywall@gmail.com
Hours: Monday through Friday, 7:00 AM to 6:00 PM