SilentFX Gypsum Board Specs: Dimensions, STC Ratings & Weight

Core Technology and Acoustic Mechanics

CertainTeed SilentFX gypsum board is engineered specifically for noise control in commercial and high-end residential construction. Unlike standard drywall that relies solely on mass to block sound, SilentFX utilizes constrained-layer damping (CLD) technology. The board features a viscoelastic polymer core sandwiched between two layers of high-density gypsum. When sound waves strike the wall assembly, the polymer layer shears microscopically, converting acoustic energy into negligible amounts of heat. This mechanical dissipation drastically reduces sound transmission, particularly in the low-to-mid frequency ranges (125 Hz to 500 Hz) where standard mass-loaded assemblies typically fail.

According to the Whole Building Design Guide (WBDG), achieving target Sound Transmission Class (STC) ratings in modern open-plan architecture requires addressing flanking paths and utilizing damping materials rather than simply adding layers of standard gypsum. SilentFX addresses this by providing the acoustic equivalent of two layers of standard 5/8-inch drywall in a single, lighter panel.

Physical Dimensions and Manufacturing Tolerances

SilentFX is manufactured to meet ASTM C1396 specifications for gypsum board, but its internal polymer layer requires strict adherence to dimensional tolerances during installation to prevent edge-stressing. The panels are available in standard imperial dimensions, with a consistent tapered edge profile designed for Level 4 and Level 5 finishing.

Acoustic Performance: STC Assembly Data

The standalone STC rating of a gypsum board is a misleading metric; acoustic performance is dictated by the complete wall or ceiling assembly. SilentFX is designed to maximize damping when paired with decoupled framing and mineral wool insulation. Below are tested STC ratings for common commercial assemblies using 5/8-inch SilentFX.

For specifications requiring an Outside-Inside Transmission Class (OITC) rating to mitigate low-frequency exterior noise (such as traffic or aircraft), SilentFX assemblies typically yield an OITC rating 5 to 8 points lower than the STC rating, which is standard for CLD-based drywall systems.

SilentFX vs. SilentFX QuickCut: Cutting Specifications

A critical specification often overlooked in procurement is the cutting methodology. The original SilentFX formulation features a highly elastic polymer core that resists standard score-and-snap techniques. Attempting to snap the board without cutting through the polymer results in jagged edges and compromised acoustic seals.

• Original SilentFX: Must be cut using a fine-tooth drywall saw, a router with a dust-extraction bit, or by deeply scoring the face paper and gypsum, snapping the core, and then slicing the remaining polymer backing with a heavy-duty hook-blade utility knife.
• SilentFX QuickCut: Formulated with a modified polymer matrix that allows for standard score-and-snap installation. This reduces labor time by approximately 30% on complex layouts involving electrical boxes and HVAC cutouts.

Electrical Box Cutout Tolerances

When cutting for electrical boxes, maintain a maximum 1/8-inch gap between the gypsum edge and the box flange. Gaps larger than 1/4-inch will create acoustic flanking paths, effectively reducing the assembly's STC rating by up to 5 points, regardless of the board's damping properties.

Framing and Fastener Specifications

To maintain the integrity of the viscoelastic core and ensure the board lays flat without screw-pops, fastener specifications must be strictly followed. The Gypsum Association's GA-600 Fire Resistance and Sound Control Design Manual mandates specific screw penetration depths for acoustic panels.

Fastener Requirements

• Screw Type: Type S (fine-thread) for steel studs under 20-gauge; Type W (coarse-thread) for wood framing.
• Screw Length: Minimum 1-1/4 inch for 1/2-inch board; minimum 1-5/8 inch for 5/8-inch board.
• Wall Spacing: Maximum 16 inches on center (o.c.) in the field; 8 inches o.c. at perimeter edges.
• Ceiling Spacing: Maximum 12 inches o.c. in the field; 8 inches o.c. at perimeter edges.
• Penetration Depth: Screw heads must dimple the face paper without breaking the paper surface. Over-driving the screw tears the paper facing, eliminating the holding power and creating a localized acoustic leak.

Perimeter Sealing and Finishing Codes

The acoustic performance of SilentFX is entirely dependent on airtight perimeter sealing. Sound behaves like water; it will exploit the smallest structural gaps.

Code Compliance Note: All perimeters, including top tracks, bottom tracks, and abutting walls, must be sealed with a non-hardening acoustic sealant meeting ASTM C919 standards. Do not use standard acrylic latex painter's caulk, as it hardens and cracks under structural deflection, breaking the acoustic envelope.

For finishing, SilentFX requires standard joint compounds. However, because acoustic walls are often installed in environments with critical lighting (e.g., home theaters, recording studios, executive boardrooms), a Level 5 finish is highly recommended. Apply a skim coat of joint compound over the entire surface to eliminate joint banding and ensure the acoustic sealant at the floor track is concealed behind the baseboard, not the drywall.