STC Rating Chart: What Each Level Blocks and What You Need

If a coworker takes a call in the next room and you can follow every word, the wall between you probably rates in the low 30s.

An STC rating (Sound Transmission Class) is a single number for how well a wall blocks airborne sound. Higher numbers block more, and at STC 50, loud sounds turn very faint.

At STARC Systems, we build reusable temporary walls for renovations in occupied hospitals and airports, where construction noise and dust carry to patients and travelers. Every STC rating we quote comes from our published specs.

STC Rating Chart and Scale

An STC rating chart pairs each number with what you hear through the wall and a real-world match.

A one- or two-point difference is inaudible to most people. A 5-point change is clearly noticeable, and a 10-point jump sounds about half as loud. Different charts place these cutoffs a few points apart, so read each row as a guide.

Background noise shifts it further. A busy room hides more of the sound next door, so the same wall feels quieter in a crowded office than in an empty one.

Two related scores share spec sheets with STC. OITC rates exterior noise from traffic and aircraft, with more weight on low frequencies. NRC, one of several acoustic ratings, scores how much sound a surface absorbs.

STC Ratings for Walls

Half-inch drywall on both sides of wood studs rates 33 to 35. Heavier or separated framing climbs from there.

CMU gets its rating from mass. Grouting fills the cores that would otherwise resonate, so grouted block rates higher than hollow.

Temporary drywall reaches the stud-wall numbers above, then comes down at the end of each phase.

Double-stud construction takes a demising wall, the permanent partition between tenants, to 60 or more.

STC Testing in the Lab and the Field

A lab builds the wall into the opening between two reverberation rooms and measures the sound level on each side. ASTM E90 sets that procedure. ASTM E413 fits the loss in sixteen bands from 125 to 4,000 Hz to a single number.

Field results typically land 3 to 10 points below the lab number, because sound flanks the wall through the ceiling plenum and the structure beside it.

The 125 to 4,000 Hz range leaves one blind spot. Speech sits inside it, while bass sits below, so STC says little about how well a wall holds bass back. Schedule the loudest work for off-peak hours.

Ask for the full E90 report when you spec a wall. It lists the loss in every frequency band, so you can see exactly where the wall loses performance.

How to Raise an STC Rating

National Gypsum names six levers that raise a wall’s STC and puts numbers on four of them:

• Mass climbs when ⅝″ board replaces ½″ or crews add layers, though returns shrink with each layer.

• Cavity absorption added 8 points in one example, and fiberglass or mineral wool gains the most. Spray foam adds little.

• Cavity depth grew with 6″ steel studs, which made room for more insulation and added 4 points.

• Stiffness drops with metal studs, which flex more than wood, and with 24″ spacing over 16″.

• Decoupling with resilient channel added 5 points, and a chase wall with two rows of studs added 14.

• Damping from a viscoelastic-core board in place of one regular layer added 11 points.

Joints and penetrations that stay unsealed pull a wall below its rated STC. ASTM C919 covers the acoustical sealants that close those flanking paths.

Reaching STC 50 takes insulation plus one more lever. A 4″ steel-stud wall with batt insulation and one ⅝″ drywall layer per face rates 47, and three builds clear 50.

Choose the second layer when floor area is tight, since it adds only ⅝″ of thickness, and choose 6″ studs when the plan has room.

Resilient channel fails when a long screw reaches the stud, so check fasteners before the board goes up.

Recommended STC Ratings by Space

Recommended STC ratings run from 35 for exam-room-to-corridor walls to 60 for mechanical rooms and MRI suites. Each group below follows the standard that sets it.

Hospitals and Clinics

FGI sets healthcare targets as composite STC, which counts the door. Unsealed doors leak sound, so exam-room-to-corridor walls sit at 35.

Classrooms and Schools

ANSI/ASA S12.60 sets the minimum for walls around a core learning space.

Offices

UFC 3-450-01 sets partition targets by room type and leaves open offices to sound masking when privacy counts.

Hotels and Tenant Walls

IBC Section 1206 sets STC 50, or 45 if field tested, for walls between dwelling units and sleeping units and from public or service areas. Hotel guest rooms and apartments follow it.

Office tenant demising walls follow the lease and project spec, and law and medical suites often need more speech privacy.

Choosing a STARC Wall for Your STC Target

Pick the wall by your sound target and fire requirement:

• FireblockWall™ carries STC 40, the highest published STARC rating, and a one-hour fire rating. Choose it when code calls for a one-hour fire-rated assembly.

• RealWall™ is the flagship for long-term, high-visibility work where appearance and quiet both count. Its foam core and sealed joints cut renovation noise by up to 50% (STC 21). It carries ASTM E84 Class A as a non-fire-rated wall.

• StackBarrier™ carries STC 20 and stretches up to 40 feet for atriums and data halls.

• LiteBarrier™ uses a single-layer fiberglass panel and suits frequently relocated work such as phased buildouts, where speed outranks maximum sound blocking.

Even the top rating of 40 sits below the 45 where privacy begins, so STARC walls cut jobsite noise for the neighbors and leave permanent privacy to permanent walls.

Hospitals weigh sound management alongside infection control, and STARC’s ICRA barriers combine both.

Two occupied jobs show the walls at work. At Fresenius Medical Care, J. Calnan & Associates used RealWall’s foam-composite panels in an occupied office through a three-phase headquarters expansion. The walls kept the space quiet and clean every phase, and employees never realized it was a construction area.

At Sarasota-Bradenton International Airport, Modular Wall Solutions installed STARC walls for an escalator renovation that needed strict noise and dust control. Managing Member Bill Bocchino said passengers walked past the double doors, oblivious that crews were cutting through structural slab behind them.

Office partitions such as folding screens and cubicle-style panels leave an opening above them, and sound takes it. Full-height walls that reach the deck or ceiling grid close it.

Not sure which wall hits your STC target? The Wall Wizard matches a system to your project in minutes, or you can request a quote and we’ll spec it for you.

Frequently Asked Questions

What is an STC rating?

An STC rating is a single number for how well a wall or door blocks airborne sound. Labs test the wall under ASTM E90 and rate the result under ASTM E413 across 125 to 4,000 Hz.

What does "rated STC" mean?

Rated STC means a wall carries a lab-tested STC number on its published test report. IBC 1206 requires a rating of STC 50 for walls between hotel guest rooms.

Is a higher or lower STC better?

A higher STC is better, because a higher number means the wall blocks more airborne sound. Staggered-stud walls reach 55 to 60, and double-stud walls reach 60 to 65.

Is an STC rating of 35 good?

An STC rating of 35 is low for privacy, because loud speech stays understandable at that level. Privacy begins near 45, and a plain drywall stud wall rates 33 to 35.

What is a good STC rating?

A good STC rating is 45 to 50 for most privacy needs. Standard private offices target 45, and conference rooms target 50.

What do STC 32 and STC 40 mean?

STC 32 lets normal and loud speech through understood, and STC 40 reduces loud speech to a murmur.

What is the STC rating of ½-inch drywall?

The STC rating of ½-inch drywall on both sides of wood studs is 33 to 35. Double layers with insulation reach 40 to 42.

What is the STC rating of an 8-inch CMU wall?

The STC rating of an 8-inch CMU wall is 48 to 52 when hollow and 51 to 54 when grouted. Grouting fills the cores, so grouted block rates higher.

How does STC differ from NIC?

STC rates a wall alone in a lab, while NIC rates the sound that reaches a room in a finished building. For the same wall, NIC typically runs 3 to 10 points below STC.