Stc Wall Calculator

Estimate the Sound Transmission Class (STC) rating of your wall assembly by selecting the components below. A higher STC rating means better soundproofing.

Estimated STC Rating: 0

Select your wall components and click calculate.

function calculateSTC() { var baseSTC = 20; // Base STC for studs alone, before adding any mass from drywall. var studTypeValue = parseFloat(document.getElementById("studType").value); var studSpacingValue = parseFloat(document.getElementById("studSpacing").value); var insulationValue = parseFloat(document.getElementById("insulation").value); var decouplingValue = parseFloat(document.getElementById("decoupling").value); var dampingValue = parseFloat(document.getElementById("damping").value); var sideA_layer1 = parseFloat(document.getElementById("sideA_layer1").value); var sideA_layer2 = parseFloat(document.getElementById("sideA_layer2").value); var sideB_layer1 = parseFloat(document.getElementById("sideB_layer1").value); var sideB_layer2 = parseFloat(document.getElementById("sideB_layer2").value); if (isNaN(studTypeValue) || isNaN(studSpacingValue) || isNaN(insulationValue) || isNaN(decouplingValue) || isNaN(dampingValue) || isNaN(sideA_layer1) || isNaN(sideA_layer2) || isNaN(sideB_layer1) || isNaN(sideB_layer2)) { document.getElementById("stcResult").innerHTML = "Error"; document.getElementById("stcDescription").innerHTML = "Invalid input. Please ensure all options are selected."; return; } var totalMassValue = sideA_layer1 + sideA_layer2 + sideB_layer1 + sideB_layer2; var totalSTC = baseSTC + studTypeValue + studSpacingValue + totalMassValue; var note = ""; // Damping compound is only effective when sandwiched between two layers of mass. if (dampingValue > 0 && (sideA_layer2 > 0 || sideB_layer2 > 0)) { totalSTC += dampingValue; } else if (dampingValue > 0) { note = " (Note: Damping compound is ineffective without a second layer of drywall on at least one side)"; } // Decoupling is a dominant factor. It makes mass and absorption more effective. var decouplingMultiplier = 1.0; if (decouplingValue > 0) { decouplingMultiplier = 1.2; // Boosts insulation effectiveness by 20% // Synergy bonus for steel studs + decoupling if (studTypeValue > 0) { totalSTC += 3; } } totalSTC += (insulationValue * decouplingMultiplier); totalSTC += decouplingValue; var finalSTC = Math.round(totalSTC); document.getElementById("stcResult").innerHTML = finalSTC; var description = ""; if (finalSTC < 30) { description = "Poor performance. Normal speech can be easily understood."; } else if (finalSTC < 40) { description = "Below Average. Loud speech is audible and fairly understandable."; } else if (finalSTC < 50) { description = "Good. Loud speech is audible but not intelligible. A common target for apartments."; } else if (finalSTC < 60) { description = "Excellent. Loud speech is heard only faintly, if at all. Ideal for home theaters."; } else { description = "Superior. Provides a very high degree of sound isolation suitable for professional recording studios."; } document.getElementById("stcDescription").innerHTML = description + note; }

What is STC (Sound Transmission Class)?

Sound Transmission Class (STC) is a single-number rating used in the United States to quantify how well a building partition, such as a wall, floor, or ceiling, attenuates airborne sound. In simpler terms, it measures how much sound a wall or other structure can block. The higher the STC rating, the more effective the partition is at reducing sound transmission, leading to quieter spaces.

How to Interpret STC Ratings

Understanding what STC values mean in the real world is crucial for planning any soundproofing project. Here is a general guide:

• STC 25-30: Poor performance. Most normal speech can be heard and understood clearly through the wall.
• STC 35-40: Below average. Loud speech is audible and can be understood. This is typical of basic, uninsulated interior walls.
• STC 45-50: Good performance. Loud speech is audible but generally not intelligible. STC 50 is often the required standard in new multi-family construction (apartments, condos).
• STC 55-60: Excellent performance. Loud music or shouting is heard only faintly or not at all. This level is ideal for home theaters, bedrooms, and offices where privacy is important.
• STC 60+: Superior performance. Provides a very high degree of sound isolation, typically required for professional applications like recording studios, cinemas, and sensitive facilities.

Key Principles of Soundproofing a Wall

Achieving a high STC rating involves applying four key principles of sound control. Our calculator models how these principles contribute to the final rating:

1. Mass: The simplest way to block sound is with heavy, dense materials. The more mass a wall has, the more sound energy is required to make it vibrate. This is why using thicker drywall (5/8″ vs 1/2″) or adding multiple layers of drywall increases the STC rating.
2. Absorption: Filling the empty air cavity within a wall with sound-absorptive material, like fiberglass or mineral wool insulation, significantly improves performance. This material absorbs sound waves that enter the cavity, reducing resonance and preventing the sound from amplifying within the wall structure. Mineral wool is denser than fiberglass and is generally a better sound absorber.
3. Decoupling: This is one of the most effective soundproofing techniques. Decoupling involves mechanically separating the two sides of a wall so that vibrations from one side cannot travel directly to the other. This is achieved with methods like using resilient channels, sound isolation clips, or building a double-stud wall.
4. Damping: Damping involves converting sound energy into a small amount of heat. This is typically done by adding a viscoelastic compound (like Green Glue) between two rigid layers, such as two sheets of drywall. As sound waves try to vibrate the wall, the damping compound shears and dissipates the energy.

Example Wall Assembly Calculation

Let's see how to build a high-performance wall for a home theater, where isolating loud movie sounds is critical.

Goal: Achieve an STC rating of 55 or higher.

Assembly Selections in Calculator:

• Stud Type: 2×4 Wood Studs
• Stud Spacing: 16 inches
• Insulation: R-13 Mineral Wool (Rockwool)
• Decoupling: Sound Isolation Clips (One Side)
• Damping: Viscoelastic Compound
• Side A: Layer 1: 5/8″ Type-X, Layer 2: 5/8″ Type-X
• Side B: Layer 1: 5/8″ Type-X

This combination utilizes mass (three total layers of heavy drywall), absorption (mineral wool), decoupling (isolation clips), and damping (viscoelastic compound). The calculator would estimate an STC rating in the high 50s or low 60s, confirming it's an excellent design for a home theater.

Disclaimer

This calculator provides an estimate for educational and planning purposes only. The final STC rating of a real-world installation depends heavily on the quality of workmanship and the mitigation of "flanking paths" (sound traveling over, under, or around the wall). For certified performance, laboratory testing according to ASTM E90 standards is required.