Technology

STC 35 vs 40 vs 45 Doors: How to Select an Acoustic Rating

28 September 2026

STC 35 vs 40 vs 45 Doors: How to Select an Acoustic Rating

Choose an acoustic doorset by room target, tested assembly and site interfaces—not by a leaf rating alone.

An STC number describes laboratory sound-transmission performance across a frequency range. A higher number generally indicates more airborne-sound reduction, but STC 35, 40 and 45 are not interchangeable product labels. The result belongs to the tested assembly and depends on the leaf, frame, seals, threshold, hardware, glazing and installation.

Use WONLY's acoustic and STC-rated entrance door specification page to turn the selected target into a doorset, evidence and site-acceptance checklist.

What the Three Ratings Mean in Practice

  • STC 35 may suit spaces needing moderate speech and activity reduction
  • STC 40 is a stronger target where clearer separation between occupied rooms is required
  • STC 45 demands tighter control of the complete opening and adjoining construction

These are planning distinctions, not guarantees of perceived silence. Low-frequency noise, background level, room size and flanking paths can change what occupants hear.

Start with the Room Requirement

Define the source room, receiving room and acceptable background condition. A hotel room beside a corridor, a meeting room, a plant room and a residential entrance have different noise spectra and privacy expectations. The acoustic consultant should coordinate the door target with the wall, floor, ceiling and ventilation strategy.

Verify the Tested Assembly

Ask for a laboratory report showing the tested leaf and frame construction, dimensions, seals, threshold, hardware and any glazing. Confirm whether the proposed opening remains inside that scope. A test for a solid, smaller specimen may not support a larger glazed door or different frame without additional assessment.

Control the Perimeter

  • Use continuous, compatible head and jamb seals
  • Specify an effective threshold seal or automatic drop seal
  • Coordinate the floor finish so the bottom gap stays within the tested condition
  • Avoid hardware preparation that interrupts seals or creates leakage paths
  • Check paired-door meeting stiles and flush bolts as part of the assembly

Treat Glazing and Hardware as Acoustic Components

Vision panels, viewers, locks, access-control cables, transfer grilles and closers can reduce performance if they differ from the tested design. Record every penetration and reinforcement in the approved drawing. If ventilation is needed, solve it through an acoustically designed path rather than an untested opening in the leaf.

Prevent Flanking Transmission

A high-rated door cannot compensate for a weak wall, unsealed frame perimeter, ceiling void or service penetration. Seal the frame-to-wall junction with the specified materials and inspect hidden gaps before finishes conceal them. Coordinate adjacent walls to meet the overall room target.

Inspect Installation and Commissioning

  • Verify frame alignment, anchors and perimeter sealing
  • Measure clearances at the head, jambs, meeting stiles and threshold
  • Confirm uniform seal compression while keeping the door operable
  • Test closing and latching after final floor finishes are installed
  • Use site acoustic testing when the specification or risk requires it

Choose the Rating Without Over-Specifying

Moving from STC 35 to 45 can affect leaf mass, thickness, hardware, closing force, frame construction and cost. Select the lowest rating that satisfies the verified room criterion with an appropriate design margin. Over-specification can create accessibility, coordination and budget problems without fixing flanking noise.

FAQ

Is an STC rating for the door leaf or the whole doorset? Project evidence should relate to the complete tested assembly. A leaf-only statement does not establish installed opening performance.

Will an STC 45 door make a room silent? No. STC addresses airborne transmission through a tested assembly and does not eliminate all frequencies, structure-borne noise or flanking paths.