Wall Soundproofing Calculator

STC Ratings and What They Mean for Your Wall

An STC rating of 33 is the number that separates "I can hear every word next door" from "I know someone is talking but cannot make out the words." That single number — the Sound Transmission Class — measures how many decibels of airborne sound a wall assembly blocks. The **Wall Soundproofing Calculator** estimates materials and costs for upgrading your wall to a higher STC rating, whether you are dealing with a noisy neighbour, a home theatre that rattles the bedroom, or a nursery that needs quiet.

A standard interior wall (single layer of 1/2-inch drywall on each side, empty stud cavity) rates STC 33. Normal speech is clearly audible through it. Adding mineral wool insulation to the cavity bumps it to STC 37–39. Mount the new drywall on resilient channel instead of directly to the studs and you reach STC 44–46 — loud speech is audible but not intelligible. Layer mass-loaded vinyl behind double drywall on resilient channel and you push past STC 55, where most household noise is effectively blocked.

Each layer in a soundproofing assembly does something different. Insulation absorbs sound energy inside the cavity, converting vibration to heat. Resilient channel decouples the drywall from the framing, breaking the mechanical path that transmits vibration. MLV adds mass without adding thickness — a 1-lb-per-square-foot sheet is only 1/8 inch thick. Double drywall adds more mass and creates a damping sandwich when combined with acoustical caulk between the layers. No single layer does the job alone. Effective soundproofing works because the layers address different parts of the sound transmission problem.

Party walls in multi-family buildings typically require a fire-resistance rating (1 or 2 hours per IBC). Adding soundproofing layers may affect the assembly's fire rating. Verify with your local building department before modifying shared walls. Some assemblies (such as resilient channel with Type X drywall) can satisfy both fire and acoustic requirements simultaneously, but this must be confirmed against the specific UL or GA fire-rated assembly listing for your wall type. Removing existing drywall from a fire-rated wall and replacing it with a non-rated assembly can violate building code and create liability.

If the wall you are soundproofing requires new framing — either because you are adding a decoupled stud wall or because the existing framing needs replacement — the [wall framing calculator](/calculators/structural/wall-framing-calculator) sizes the stud layout and material quantities for the new wall section.

Insulation Types: Fiberglass vs. Mineral Wool

Both fiberglass and mineral wool fill the stud cavity and absorb sound, but they are not equally effective. Choosing the right insulation is the single decision that costs the least to get right and the most to get wrong — you only get one chance to fill the cavity before it is sealed behind drywall.

**Mineral wool (Roxul / Rockwool Safe'n'Sound)** is denser than fiberglass — typically 2.5 to 4 lbs per cubic foot versus 0.5 to 1.0 lbs for fiberglass. That density absorbs more low-frequency sound, which is exactly the bass-heavy noise that travels through walls most effectively. Mineral wool is semi-rigid, so it friction-fits between studs without sagging or slumping over time. It is also non-combustible and resists moisture. At $1.10 per square foot (March 2026 US average), mineral wool costs about 57% more than fiberglass — but the acoustic performance difference is worth every cent in a dedicated soundproofing project.

**Fiberglass batts** are the cheaper option at $0.70 per square foot. Standard R-13 fiberglass batts fit a 2×4 stud cavity and provide moderate sound absorption. Fiberglass is lighter, easier to cut, and widely available. For a basic soundproofing job where the goal is reducing general noise rather than achieving a specific STC target, fiberglass is adequate. The limitation shows up in low-frequency performance: fiberglass batts lack the mass to absorb bass, so television sound, music, and footfall noise pass through more readily than through mineral wool.

For most soundproofing projects, mineral wool is the better investment. The $0.40 per square foot premium over fiberglass adds only $48 to a 120-sq-ft wall — a small fraction of the total project cost — and delivers measurably better results across the frequency range that matters most in residential settings.

The material costs in this calculator cover the soundproofing assembly itself. If the project involves finishing the new drywall layers with tape and compound, the [drywall joint compound calculator](/calculators/materials/drywall-joint-compound-calculator) estimates compound, tape, and corner bead quantities based on sheet count and finish level.

Material Requirements by Method

The four soundproofing methods in this calculator represent increasing levels of noise reduction. Each method adds layers to the wall assembly, and each layer contributes a measurable STC improvement. The table below shows what each method includes and the approximate STC range you can expect.

| Method | Layers Included | Approx. STC | Best For | |---|---|---|---| | Basic | Cavity insulation only | 37–39 | General noise reduction on a budget | | Standard | Insulation + resilient channel + single drywall | 44–46 | Shared bedroom walls, home offices | | Premium | Insulation + MLV + double drywall | 48–52 | Apartment party walls, nurseries | | Maximum | Insulation + resilient channel + MLV + double drywall | 55–60 | Home theatres, music rooms, studios |

All STC ratings assume mineral wool insulation in a standard 2×4 stud cavity with 5/8-inch drywall. Fiberglass insulation reduces each rating by 2–3 points. Existing STC depends on the starting wall condition — an open stud cavity starts at STC 20, while a single-drywall wall starts at STC 33. Prices as of March 2026, based on US national averages from RS Means Interior Construction Cost Data.

The jump from basic to standard is the most cost-effective upgrade. Resilient channel costs $1.50 per linear foot and a single layer of drywall runs $14 per 4×8 sheet — together they add 7–9 STC points. The jump from premium to maximum adds resilient channel to the MLV-and-double-drywall assembly, gaining another 3–5 STC points for $1.50 per linear foot of channel. Diminishing returns set in above STC 55: each additional point costs more and delivers less perceptible difference.

Sealing the Gaps: Where Most DIY Soundproofing Fails

Sound behaves like water — it finds the smallest gap and pours through it. A wall with STC 55 materials but a 1/4-inch gap at the bottom plate performs like STC 35 at best. Sealing is the step most DIYers skip or under-do, and it is the single most common reason soundproofing projects disappoint.

**Where do sound leaks happen?** Every perimeter edge of the drywall — top, bottom, and sides — must be sealed with acoustic sealant (not regular caulk). Electrical outlets and switch boxes are the worst offenders: a standard single-gang box creates a hole through the wall that leaks sound directly into the next room. Light fixtures, HVAC registers, and plumbing penetrations are equally problematic. The gap between the bottom of the drywall and the floor is another common leak point that regular baseboard trim does not seal.

**What is acoustic sealant and why not regular caulk?** Acoustic sealant (also called acoustical caulk) remains permanently flexible. It never fully cures, which means it maintains its seal even as the building settles and framing moves seasonally. Regular silicone or latex caulk cures hard, then cracks as the wall moves — and every crack is a sound leak. One tube of acoustic sealant covers roughly 32 linear feet from a standard caulk gun. At $8 per tube (March 2026 US average), it is the cheapest material in the entire assembly and the one you should never skip.

**How do I handle electrical outlets?** Move outlets on opposite sides of the wall so they are not back-to-back — stagger them by at least one stud bay. Seal around every electrical box with acoustic sealant. For maximum performance, install acoustic putty pads (pre-formed putty sheets) over the back and sides of each box. These pads add mass and seal the box without interfering with wiring.

**Does door and window sealing matter?** Absolutely. A hollow-core interior door with a 1/8-inch gap at the bottom has an STC of about 15. No amount of wall treatment compensates for a door that leaks sound. If the room has an interior door, upgrading to a solid-core door and adding perimeter weatherstripping is as important as treating the walls.

Installation Sequence for a Soundproofed Wall

The order of operations in a soundproofing project matters more than the materials themselves. Installing layers in the wrong sequence creates gaps that compromise the entire assembly. If your project involves thermal insulation in addition to acoustic treatment, the [insulation requirement calculator](/calculators/materials/insulation-requirement-calculator) helps determine R-value targets for your climate zone.

1. **Remove existing drywall (if applicable).** Strip the drywall from the side of the wall you are treating. Pull all nails and screws from the studs. Inspect the cavity for plumbing, wiring, and HVAC runs — these will need to be worked around. Dispose of old drywall before proceeding; the dust interferes with adhesion of sealant.

2. **Install insulation in the stud cavities.** Press mineral wool or fiberglass batts into each stud bay. Mineral wool friction-fits without fasteners. Cut insulation to fit snugly around pipes and wires — no gaps, no compression. A compressed batt loses both thermal and acoustic performance.

3. **Apply MLV to the stud face (premium and maximum methods).** Staple or screw MLV sheets directly to the stud faces, overlapping seams by 2 inches. Seal every seam with MLV seam tape. The MLV layer must be continuous — any gap in the membrane is a sound leak. Cut carefully around electrical boxes and seal the edges with acoustic sealant.

4. **Install resilient channel (standard and maximum methods).** Screw resilient channel horizontally to the studs, spaced 16 inches on centre, starting 6 inches from the floor. Channels must not touch the floor, ceiling, or side walls — leave a 1/4-inch gap at all perimeters. This gap is what creates the decoupled air space. If a channel screw punches through into the stud behind the channel flange, it short-circuits the decoupling — use the correct screw length (1 inch for channel to stud, no longer).

5. **Hang drywall and seal all edges.** Screw drywall to the resilient channels (not to the studs — a single screw into a stud defeats the decoupling). Run a bead of acoustic sealant at the top plate, bottom plate, and where the drywall meets side walls. For double drywall, apply acoustic sealant or Green Glue compound between the two layers, then screw the second layer through the first into the channels.

6. **Seal all penetrations.** Caulk around every electrical box, pipe, and duct penetration with acoustic sealant. Install putty pads behind outlet boxes. Seal the gap at the floor with sealant before installing baseboard. Check for daylight around every edge and penetration — if light passes through, sound will too.

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