Reference

Sound and Fire-Rated Assemblies

The published sound and fire ratings of the wall and ceiling builds the calculators count, each with where the number comes from.

Last updated

Sound: STC of common walls

Assembly Board each side Insulation Lab STC Source
Single 2 × 4 studs 1 layer / 1 layer none 33–35 GA-600 single-stud listings; published lab summaries
Single 2 × 4 studs 1 / 1 batts 34–39 GA-600 listings; published lab summaries
Single studs, two layers one side 1 / 2 batts 41–44 Published lab summaries
Single studs, resilient channel one side 1 / 2 on channel batts 48–52 Published lab summaries; depends on installation
Staggered 2 × 4 studs on a 2 × 6 plate 1 / 1 batts 46–49 Published lab summaries
Staggered studs, 5/8 in type X 2 / 2 batts 50–54 GA-600 file WP 3910 (2-hour)
Double row of 2 × 4 studs, 1 in apart 2 / 2 batts 55–59 GA-600 file WP 3810 (2-hour)

STC (sound transmission class) is measured in a laboratory. Built walls usually test 3 to 5 points lower (ASTC), because sound goes round the wall through floors, ducts, outlets and gaps. Damping compound between two layers adds several points in its makers’ tests; the gain belongs to the specific tested build, not to any wall.

STC What you hear through the wall (a common rule-of-thumb scale)
30–35 Normal speech understood
40–45 Loud speech heard but hard to understand
50–55 Loud speech barely heard; music bass still comes through
60+ Most household sound blocked

The building code (IBC 1206) requires STC 50 (45 if field tested) between dwelling units in multifamily buildings; it sets nothing for walls within one home.

Fire: rated assemblies

Assembly Board Rating Source
2 × 6 studs at 16 in one layer 5/8 in type X each side, screws at 7 in 1 hour GA-600 file WP 3660
As above with 5-1/2 in mineral fibre one layer 5/8 in type X each side, screws at 12 in 1 hour GA-600 file WP 3661
Wood-stud partition two layers 5/8 in type X each side 2 hours GA-600 two-hour listings such as WP 4135
Staggered studs two layers 5/8 in type X each side 2 hours GA-600 file WP 3910
Double wood-stud wall two layers 5/8 in type X each side 2 hours GA-600 file WP 3810
Floor-ceiling one or two layers 5/8 in type X or type C below, often on resilient channel 1 or 2 hours GA-600 floor-ceiling (FC) listings

A rating belongs to the whole tested assembly: the board, its layers, the fasteners and their spacing, the joint treatment, and often the stud size and insulation. Change a part and the listing no longer applies. Find the listing in GA-600 or a manufacturer’s test report and follow it exactly; the building department decides what it accepts.

Garage separation (one- and two-family homes)

Separation Minimum board on the garage side
Garage from the house and its attic 1/2 in gypsum board
Garage from habitable rooms above 5/8 in type X
Structure supporting that floor-ceiling 1/2 in gypsum board
Garage within 3 ft of the house on the same lot 1/2 in on the interior side of the exterior walls

These are prescriptive requirements of the International Residential Code, Table R302.6, not rated assemblies. Local amendments vary.

Sources

Gypsum Association GA-600, Fire Resistance and Sound Control Design Manual (files WP 3660, WP 3661, WP 3810, WP 3910 and the two-hour partition and floor-ceiling listings); published laboratory test summaries for the STC ranges of untested combinations, labelled as such; International Building Code section 1206; International Residential Code Table R302.6.

Calculators that use this table

The guides to soundproofing a wall, soundproofing a ceiling, fire-rated assemblies and garage fire separation explain the figures.