Catalog Of STC And IIC Ratings For Wall And Floor/Ceiling .

Catalog of STC and IIC Ratings forWall and Floor/Ceiling AssembliesRussell B. DuPreeOffice of Noise Control, California Department of Health ServicesBerkeley, California 94704IntroductionThis catalog of sound-rated wall andfloor/ceiling assemblies was compiled fromlaboratory test reports submitted to the California Office of Noise Control by variousmanufacturers, trade associations andgovernment agencies. It contains STC(Sound Transmission Class) or IIC (ImpactInsulation Class) ratings for approximately500 different construction assemblies. Eachassembly has been assigned a unique reference number through an index system. Testsummaries were reviewed by the submittingorganizations and are produced here withtheir permission.The catalog is intended to aid California Building Officials in determining compliance with the state's noise insulation standard for multifamily housing (Section 1092of Title 25 of the California AdministrativeCode). It may be used to evaluate a givenconstruction assembly or to compare assemblies of different types. Although the catalog contains data on many commonly usedwall and floor/ceiling designs, other laboratory tests may be considered in evaluatingan assembly for compliance with the standard. Architects, builders and other designprofessionals may also find the catalog useful in selecting assemblies which providegood noise insulation.How to use the catalogThe catalog is divided into sections andsubsections which indicate major differencesin acoustic performance and constructiontype. Section headings are listed in theindex along with the level and number ofthe sections. A hierarchy of section levels isproduced by a series of numbers, each followed by a period. For example, secondlevel section headings are indicated by twonumbers followed by periods; third levelsection headings by three numbers followedby periods, and so forth. Similar techniquesfor section hierarchy are used in most basicbuilding codes.The purpose of the indexing system isto enable the user to quickly find a group ofconstruction assemblies having similarsound transmission characteristics. Mostsection headings were selected to group theassemblies according to the followingacoustically important properties:massstructural continuitydepth of air cavitycavity absorptionThere are five section heading levels in theindex. Each section level is indented fromthe preceding level and printed in a smallertype size. The number in parenthesis afterfifth level section headings is the number oftests in that section. Many fifth level section headings show no tests at all, nevertheless they are listed in the index in order tomaintain continuity and to allow for additions to the. catalog at a future date. Agiven party wall or floor/ceiling assemblymay be located in the 'catalog by selectingthe appropriate headings from the index,starting with the first level and continuingthrough the fifth level.The following example illustrates howto locate a given wall type in the index:Assume that the architect's drawings show aparty wall similar to the one below. It ismade up of 2x4 studs spaced 16"o.c. andstaggered 8"o.c. on 2x6 plates. The wallfaces are 1/2" gypsum board and the cavityis filled with a 3 1/2" thick porous insulatingmateria1.In the index there is a group of wallassemblies similar to the one describedabove. To find that group, first look at all

section headings which contain only onenumber. There are two of them" 1.Wall assemblies “ and 2. Floor assemblies “. This example is obviously a wallassembly, so all sections which begin withthe number 2. can be disregarded.The next step is to look for theappropriate second level section heading.From the index, the choices are:-““1.1.1.2.1.3.1.4.“Studless wallsWood stud wallsMetal stud wallsMasonry wallsThe correct choice here would be1.2.Wood stud walls “.1.2. “,Under the section headingthe choices for third level section headingsare:““1.2.1. Single wood studs,no decoupling connectors1.2.2. Single wood studs,with decoupling connectors1.2.3. Staggered wood studs on single plates1.2.4. Double wood studs on separate PlatesHere the correct choice is 1.2.3. Staggered wood studs on single plates “.“Now the choices for fourth level section headings are:1.2.3.1. One leaf each face1.2.3.2. Two leaves each face1.2.3.3. Three leaves each face1.2.3.4. More than three leaves each face1.2.3.5. Unbalanced(dissimilar number of leaves each face)1.2.3.6. Plaster facedAnd the correct choice here isOne leaf each face “.“1.2.3.1.For the fifth and final section headinglevel, choose among the 1.2.3.1.5.1.2.3.1.6.1.2.3.1.7.Leaf thicknessLeaf thicknessLeaf thicknessLeaf thicknessLeaf thicknessLeaf thicknessLeaf thickness 1/4"1/4"3/8"1/2"5/8"314" 1"Since the face leaves of this example are1/2" thick, the correct choice is 1.2.3.1.4.Leaf thickness 1/2".“Now the search for a comparable testreport has been narrowed to a few assemblies which are listed in section 1.2.3.1.4.To find this section in the catalog, simplylook at the right hand column under "Section Number" and follow the sequence ofnumbers until you come to 1.2.3.1.4. (onpage 50). You will notice that there areeleven tests listed and that the fourth test inthe group (1.2.3.1.4.4) matches the description in the example.Each assembly in the catalog is drawnto a scale of one inch one foot andpresented beside a summary description ofthe assembly components. Other information given on each assembly includes thename of the laboratory which tested theassembly, the test number designated by thelaboratory, the year, the number of frequencies tested (either 11 or 16) and the nameof the organization which supplied the datafor this catalog. The STC and IIC ratingsare shown in bold face type in anothercolumn. The column with the three dots isfor information which may be added at afuture date. Occasionally information wasnot available and is so indicated by theletters "NA".Laboratory and field testsThe single number ratings STC andIIC are determined in a special laboratorysetting. This setting is designed so that allsound from the source room is transmittedto the receiving room only through the testassembly. The sound pressure levels in thesource and receiving rooms are averagedover time and space in 16 different frequency bands, Then the measured levels,or differences in levels, are evaluated byrules which yield a single number ratingcalled the Sound Transmission Class or theImpact Insulation Class. This rating can becompared with the results of other laboratory tests which use the same rating procedure. It is important to understand thatthe laboratory procedure is designed tomeasure only the sound transmitted by thetest assembly.In the field, however, tests are usuallymade to determine the amount of soundtransmitted from one room to anotherregardless of the sound path. In a properlyconstructed building, most of the sound

energy will be transmitted by the separatingassembly itself, but there are many opportunities for "flanking paths" or "sound leaks"to occur. Some of the common airbornesound transmission flanking paths in buildings are:plenums and suspended ceilingsunbaffled ductswindow to window (outdoors)common heating unitstransoms and air grillesunblocked joist spacesuncaulked wall perimetersducts, piping and fixturesmasonry jointsSince a great deal of acoustic energy istransmitted through small air gaps or rigidconnectors, party walls and floor/ceilingsmust be carefully designed and built. It isnot enough that the architect select a goodsound insulating assembly; he must alsospecify properly all connections, seals, penetrations and adjacent framing of the assembly.Significance of laboratory testsLaboratory tests are made under carefully controlled conditions. There will, however, be differences in test results amonglaboratories for assemblies which are ofsimilar design and materials. Even a laboratory Performing a series of tests on oneassembly will not get Precisely the sameresults for each test. There are many reasons for this. Some of them relate to thephysical configuration of the laboratories andthe techniques for measuring sound pressurelevel. Others relate to subtle differences inmaterials and details of construction. It isnot uncommon to find differences of one ortwo STC points for similarly designedassemblies due to the differences betweenlaboratories and test specimens. Occasionally, however, there will be large differences(5 or 6 points) in laboratory STC ratings foressentially similar assemblies. This is usually because there is a pronounced dip in thetest curve and the STC rating is heavilyinfluenced by a measurement in one frequency band.The standard requires a minimumlaboratory STC rating of 50 for party wallsand floor/ceilings. All too often thisbecomes something of a "magic number". Itis not quite reasonable to reject onecompany's test showing an STC of 49 andapprove another's of a similar design whichshows an STC of 50. Nevertheless, STC 50is the minimum rating by state law. Whendiscrepancies appear among laboratory STCratings for essentially similar assemblies, andwhen the discrepancies are above and belowSTC 50, field testing may be required toassure that the building complies with thestandard.Field tests are useful in determiningthe amount of noise isolation between dwelling units in a particular project but theyshould not be used for certifying the generalapproval of a wall or floor/ceiling design.The Building Official should rely on laboratory tests during the plan review phaseunless the project sponsor agrees to a fieldtest of the completed building. The fundsfor field testing must then be in escrowbefore the building permit is issued.Flanking paths and sound leaks do notinfluence laboratory tests, therefore thesetests will not necessarily indicate the amountof noise isolation actually achieved in acompleted building. Yet it is the isolationthat the occupant is concerned with, not theinsulation rating (STC) of the assembly.Field tests are, therefore, quite important inassuring that the minimum amount ofacoustic privacy is achieved. Field tests maynot be needed on every project, but theBuilding Official should require a field testwhenever he notes that the structure hasbeen compromised by flanking paths,

Wall and Floor/Ceiling Assemblies Russell B. DuPree Office of Noise Control, California Department of Health Services Berkeley, California 94704 Introduction building codes. This catalog of sound-rated wall and The purpose of the indexing system is floor/ceiling assemblies was co