Drywall Types and Specifications

Drywall panels are classified by core composition, facing material, dimensional tolerances, and fire- or moisture-resistance ratings — each classification carrying distinct installation requirements, code applicability, and inspection implications. The U.S. construction industry is governed by standards from ASTM International, the American Gypsum Association (AGA), and adopted building codes including the International Building Code (IBC). Selecting the correct panel type affects structural performance, fire egress ratings, and compliance with both federal and local authority having jurisdiction (AHJ) requirements. The drywall listings on this platform are organized in part by the types of panel systems and specialty installations contractors service.

Definition and scope

Drywall — also referred to as gypsum board, wallboard, or plasterboard — consists of a gypsum plaster core pressed between two layers of paper facing. ASTM International publishes the primary classification standard for gypsum board products: ASTM C1396/C1396M, which defines dimensional, physical, and performance requirements across product categories. The standard covers panels ranging from the nominal ½-inch residential type to specialty assemblies used in fire-rated construction.

Scope within the U.S. construction sector spans residential, commercial, and industrial applications. Panel types differ by:

The drywall-directory-purpose-and-scope page describes how the National Drywall Authority classifies contractor specializations in relation to these product categories.

How it works

Product Classification by Type

Gypsum board products are differentiated through a structured hierarchy defined in ASTM C1396 and supplemented by UL (Underwriters Laboratories) fire-resistance directories:

  1. Regular (Type R) — Standard gypsum core; primary use in interior partitions and ceilings where no special fire or moisture performance is required. Nominal thickness: ½ inch or ⅝ inch.

  2. Type X — Contains glass fibers and other additives within the core to slow the spread of fire. Achieves fire-resistance ratings when installed in UL-listed assemblies. Minimum core thickness for Type X classification is ⅝ inch per ASTM C1396. Required by the IBC in specific occupancy types, including Type I and Type II construction.

  3. Type C — An enhanced version of Type X with a greater proportion of glass fibers and a shrinkage-compensating vermiculite additive. Provides extended fire performance and is used in assemblies requiring ratings of 2 hours or more.

  4. Moisture-Resistant (MR / "Green Board") — Paper-faced board with moisture-resistant core treatment. Appropriate for areas with elevated humidity but not for direct water contact. ASTM C1396 limits use in wet areas.

  5. Glass-Mat Gypsum (ASTM C1178 / C1177) — Replaces paper facing with fiberglass mat, providing superior mold and moisture resistance. Used as a tile backer in wet areas and as exterior sheathing.

  6. Flexible Drywall — Thin-profile (¼ inch) panels designed for curved surfaces; installed in two layers for compliance with standard assembly specifications.

  7. Abuse-Resistant / Impact-Resistant — Reinforced core and/or facing for high-traffic commercial environments; classified under ASTM C1629, which defines Surface Abrasion, Indentation, and Soft-Body Impact resistance levels (I, II, III).

Fire Rating Mechanism

Fire-resistance ratings are not a property of the panel alone — they attach to the entire assembly as tested under ASTM E119 or UL fire tests. The UL Fire Resistance Directory documents tested assemblies. AHJs require specification of the full assembly number, not merely the panel type, when permitting fire-rated walls or floor-ceiling systems.

Common scenarios

Residential new construction — Standard ½-inch Type R on interior walls; ⅝-inch Type X on garage-to-house separations, per IBC Section 406 and the International Residential Code (IRC) Section R302. Garage separation walls require a minimum 1-hour fire-rated assembly in attached garage configurations.

Commercial tenant improvement — Type X or Type C in rated corridor and stair shaft assemblies; ASTM C1629 abuse-resistant panels in schools, hospitals, and correctional facilities. The IBC occupancy classification drives panel selection before the permit application stage.

Wet areas (bathrooms, kitchens) — Glass-mat gypsum board (ASTM C1178) or cement board is required behind ceramic tile in shower enclosures. MR ("green board") does not meet IRC R702.4.2 requirements for use directly behind tile in wet shower areas — a distinction frequently cited in building inspection failures.

Exterior sheathing — Glass-mat exterior gypsum sheathing (ASTM C1177) functions as a weather-resistant substrate behind cladding systems; it is not a water-resistive barrier unless the product carries a WRB designation.

Sound attenuation applications — Damped gypsum panels (e.g., products meeting STC criteria) are specified for party walls in multi-family construction. Sound Transmission Class (STC) ratings are assembly-dependent, tested under ASTM E90.

Decision boundaries

Panel selection crosses from contractor discretion into code-mandated territory at three primary thresholds:

  1. Occupancy and construction type — IBC Table 601 and Section 703 define where fire-resistance-rated assemblies are required. These requirements are not performance-optional; they are triggered by building height, occupancy group, and construction classification.

  2. Wet area demarcation — IRC R702 and IBC Section 1210 define specific substrate requirements by location. The transition from "wet" to "damp" to "dry" zones determines whether glass-mat, MR board, or standard gypsum is code-permissible.

  3. Assembly integrity vs. component substitution — Substituting a Type C panel for a Type X panel within a listed UL assembly is not automatically permitted unless the alternative assembly is independently listed. AHJs may require engineering documentation for substitutions.

Permitting implications: fire-rated assemblies require inspection before concealment. Most AHJs conduct framing and drywall inspections as distinct phases. The how-to-use-this-drywall-resource page describes how contractors with fire-rated assembly experience are categorized within this directory.

Thickness tolerances, fastener schedules, and joint treatment specifications are governed by the Gypsum Association's GA-216 (Application and Finishing of Gypsum Panel Products), which AHJs reference alongside ASTM standards during inspection.

References

Explore This Site

Regulations & Safety Regulatory References Tools & Calculators Board Footage Calculator