STC Ratings Explained – A Powerful Guide to Quieter Spaces

what are STC Ratings

Have you ever been kept awake by noisy neighbors or struggled to concentrate in a loud office environment?

Sound Transmission Class ratings, or STC ratings, play a crucial role in creating comfortable living and working spaces by reducing noise levels and improving acoustic comfort.

In this blog post, you will learn about the importance of STC, the factors that influence them, and how to improve soundproofing in various environments.

Short Summary

  • STC ratings measure the sound reduction capabilities of building materials, with ratings ranging from 0-100.
  • High STC ratings help reduce noise transmission and create a focused environment in residential, commercial and educational spaces.
  • Low-frequency noise requires alternative solutions such as acoustic panels for improved insulation.

Check out my guide to inexpensive soundproofing by which you can improve the STC of your room without breaking the bank.

The Importance of STC

STC ratings are essential for maintaining a peaceful atmosphere in various environments, such as residential spaces, commercial buildings, and educational institutions. It can help you find out how much sound isolation is being provided.

The ability to block unwanted noise and provide acoustic comfort is crucial for the well-being of occupants and the efficiency of daily activities.

Residential Spaces

In residential spaces, a good STC rating ensures that your home remains a sanctuary from the noisy world outside.

Imagine trying to relax in your living room while being bombarded with traffic noise, or attempting to sleep while your neighbor’s television blares through the wall.

An effective sound barrier can make all the difference in creating a tranquil living space, which is why the International Building Code mandates an STC rating of 50 for multifamily construction.

Commercial Buildings

In commercial buildings, STC ratings are vital for creating a productive work environment. Excessive noise can distract employees, hinder concentration, and decrease overall efficiency.

By utilizing materials and construction techniques with high STC, businesses can reduce noise transmission between offices, conference rooms, and other shared spaces, promoting a more focused and productive atmosphere.

Educational Institutions

Educational institutions also benefit from high STC ratings. A quiet and peaceful atmosphere is essential for successful learning, as it enables students to concentrate and absorb information more effectively.

By employing materials with higher STC in classrooms, libraries, and lecture halls, educational institutions can create an environment that fosters optimal learning conditions.

Fundamentals of Sound Transmission Class (STC)

sound transmission class rating

The Sound Transmission Class rating system is the most common sound reduction measurement and offers a standardized method for measuring the sound reduction capabilities of building partitions.

Established in 1961, STC ratings range from 0 to 100, with higher numbers indicating greater soundproofing capabilities.

However, it is essential to note that ratings have limitations and should not be solely relied upon when specifying a soundproofing system.

Definition of STC

STC is an acronym for Sound Transmission Class, a numerical measure used to indicate the effectiveness of a partition in attenuating airborne sound.

It is expressed on a scale of 0 to 100, with higher numbers indicating greater soundproofing capabilities.

The commonly accepted STC rating for an effective sound barrier is typically between 45 and 55.

Measuring Sound Reduction

To determine the STC value, Transmission Loss (TL) values are measured at sixteen frequencies in accordance with ASTM E413, Classification for Rating Sound Insulation.

The STC rating is then calculated as a weighted average of the transmission loss values, normalized according to the area of the common partition and the absorption in the receiving room.

The higher the STC value, the better the rating and the better the performance.

Limitations of STC

STC has several limitations, particularly when it comes to addressing low-frequency noise.

The STC rating system only considers frequencies as low as 125 Hz, which may not accurately represent the material’s effectiveness in reducing low-frequency noise such as bass sounds or loud conversations.

Additionally, STC ratings are based on laboratory tests, which may not accurately reflect real-world conditions.

Therefore, it is crucial to consider additional factors such as material properties, construction techniques, and room acoustics when specifying a soundproofing system.

STC Rating Chart

The STC rating chart provides a visual representation of the sound transmission class ratings for different materials, illustrating the amount of sound transmission being reduced and the frequencies of sound being affected.

By consulting an STC rating chart (see it below), you can make informed choices about the soundproofing materials you need to create a comfortable environment in residential, commercial, or educational spaces.

STC RatingSound Transmission Characteristics
25Very poor – Normal speech easily understood
30Poor – Normal speech easily heard and understood
35Fair – Loud speech can be understood
40Good – Loud speech heard but not understood
45Very Good – Loud speech barely audible
50Excellent – Faintly hear very loud sounds
60Superior – Faintly hear shouting or hammering
70+Outstanding – Virtually no sound transmission
STC rating chart. Source: Wikipedia

Keep in mind that other factors, such as material properties, construction techniques, and room acoustics, should also be considered when selecting soundproofing materials.

STC Ratings of Materials

STC ratings vary depending on the material used in the construction of walls, windows, doors, and floors. Understanding the STC ratings of different materials is important to make informed decisions when planning a soundproof construction project.

By selecting materials with higher STC ratings, you can improve the soundproofing capabilities of your space and create a more comfortable environment for occupants. Here are the STC ratings of materials that will be discussed in this section:

Material/ApplicationSTC Rating
Regular Single-pane Window27
Double-glazed Window29
Soundproof Window48-54+
Common Wall Assembly (Common)50
Wall Assembly with soundboards55-60
Solid Wood Door30-35
Standard Steel Door25-35
Acoustic Door40-70+
Basic Wood Structure Floor/Ceiling40-43
Six-inch Concrete Sub-Floor52-55
STC ratings of materials

Check out my list of top 10 Soundproofing Materials.

STC Ratings for Windows and Glass

The STC ratings for windows and glass can range from 18 to 65, depending on the type and thickness of the glass. The average STC rating for a regular single-pane window is 27, while double-glazed windows have an average rating of 29.

However, soundproof windows can have an STC rating of 48-54 or higher, providing significantly better sound isolation.

Understanding the STC ratings for windows and glass is crucial when planning a soundproof construction project, as the right choice can make a significant difference in the overall acoustic performance of the space.

STC Ratings for Wall Assemblies

Wall assemblies can achieve various STC ratings depending on the materials and construction methods used. The most commonly requested rating is STC 50, which provides a good balance between sound isolation and construction cost.

Some wall assemblies can achieve even higher STC ratings, such as a wall with an inner layer of 12mm soundboard on both sides and an outer layer of 16mm soundboard on both sides. Type X gypsum wallboard, which can have an estimated STC rating between 55-60.

Understanding the STC ratings for wall assemblies is essential for designing a space with the desired level of soundproofing.

STC Ratings for Doors

Doors can have varying STC ratings depending on their construction and materials. Solid wood doors typically have an STC rating between 30 and 35, while standard steel doors often have an STC rating in the 25-35 range.

Acoustic doors, designed for soundproofing purposes, usually have the highest STC ratings, ranging from 40 to 70+.

When selecting a door for a soundproof construction project, it is crucial to consider its STC rating to ensure that it provides the desired level of sound isolation.

STC Ratings for Floors

Floor STC ratings measure the soundproofing capabilities between two rooms, with higher ratings indicating good sound isolation.

A basic wood structure floor/ceiling typically has an STC rating of 40-43, while a six-inch concrete sub-floor has a rating of 52-55.

Understanding the STC ratings for floors is essential when designing a space that requires soundproofing, such as an apartment building or a commercial space with multiple floors.

Factors Influencing STC Ratings

Various factors influence the STC ratings of building materials and assemblies, including material properties, construction techniques, and room acoustics.

Understanding these factors can help you make informed decisions when selecting materials and designing a space that offers the desired level of soundproofing.

Material Properties

Material properties play a significant role in determining the STC ratings of building materials. Density, thickness, and volume fraction are critical factors that can impact a material’s ability to block sound transmission.

Materials with higher mass and density, like a concrete block wall, generally have higher STC ratings than materials with lower mass and density, like wood.

Additionally, a material’s ability to vibrate or resonate at the same frequency as the source of the noise, called a coincidence dip, can result in weakness at a specific frequency, affecting the overall STC rating.

Construction Techniques

Construction techniques can also have a significant influence on the STC rating of a material. Factors such as cavity absorption, cavity depth, decoupling, damping, spacing of the studs, and gauge of the studs can all affect the sound insulation of a material.

Specifically, cavity absorption and cavity depth can boost the sound isolation, while decoupling, damping, spacing of the studs, and gauge of the studs can reduce it.

Paying close attention to construction techniques and details can ensure that your building project meets the desired STC rating and provides the necessary level of soundproofing.

Room Acoustics

Room acoustics, including the amount of insulation and installation process, can significantly influence the STC rating of a material. The amount of insulation can increase the sound isolation abilities of a material, while the installation process can reduce it.

Ensuring proper insulation and installation can help achieve the desired STC rating and create a comfortable environment for occupants.

Improving Soundproofing with Higher STC Ratings

Adding mass and insulation can improve soundproofing with higher STC ratings

To improve soundproofing with higher STC ratings, it is essential to consider various factors, such as adding mass and insulation, creating air gaps, and utilizing resilient materials.

These strategies can help you enhance the soundproofing capabilities of your space and create a comfortable living or working environment.

Adding Mass and Insulation

One of the most straightforward methods of increasing sound transmission class significantly is to add mass to the walls or floor/ceiling assembly.

Adding mass and insulation to the partition can enhance STC by increasing the overall thickness and sound absorption capabilities of the material.

This can be achieved by using thicker walls or adding insulation materials within wall cavities.

Creating Air Gaps

Creating air gaps in the construction of walls or floor/ceiling assemblies can also improve STC.

The air gap acts as a barrier that impedes sound transmission through walls, thus providing for more effective sound insulation. This can be achieved by using resilient channels or constructing a double wall with an air space between the two walls.

Resilient channels are metal strips that are attached to the studs of a wall and act as a decoupling element. This decoupling element helps to reduce sound transmission through sound.

Utilizing Resilient Materials

resilient channel increases STC

Resilient materials can be employed in construction to reduce noise transmission and absorb shock, thereby improving the durability and longevity of a structure.

Examples of resilient materials include rubber, foam, and other flexible materials that can absorb sound and vibration.

Incorporating resilient materials into your construction project can enhance the STC rating and provide a more comfortable and quiet environment for occupants.

Real-World Application of STC

In real-world applications, STC ratings are used to evaluate the efficacy of building materials in blocking low frequency and high frequency sounds.

This involves laboratory and field testing, adherence to building codes and standards, and careful product selection and installation.

Considering these factors in conjunction with STC can help ensure the desired soundproofing and performance is achieved.

Laboratory vs. Field Testing

STC is determined through laboratory and field testing. Laboratory testing is conducted in a controlled environment, while field testing is performed in the actual setting where the material will be used.

It is important to note that the measured field STC rating is often approximately five points lower than the laboratory rating due to real-world conditions.

Therefore, when constructing critical partitions, it is advisable to include a safety margin that considers the anticipated in-field acoustical performance.

Building Codes and Standards

Building codes and standards set regulations that specify the minimum STC rating for building materials. For instance, the International Building Code mandates an STC rating of 50 for multi-family construction.

Adhering to these regulations ensures that buildings are constructed with materials that provide suitable soundproofing, creating comfortable environments for occupants.

Product Selection and Installation

Proper product selection and installation are critical for achieving the desired STC rating and soundproofing performance. When selecting materials for your construction project, consider factors such as material properties, construction techniques, and room acoustics.

Additionally, ensure that the installation process is carried out correctly to achieve the maximum soundproofing potential of the chosen materials.

Addressing Low-Frequency Noise with STC

Low-frequency noise can be difficult to address with STC due to its limitations in measuring frequencies as low as 125 Hz.

To effectively reduce low-frequency sound vibration, alternative solutions such as soundproofing foam or acoustic panels may be necessary.

Limitations in Low-Frequency Noise Reduction

STC is limited when it comes to reducing low-frequency noise, such as bass sounds or loud conversations.

This is because the rating system only considers frequencies down to 125 Hz, which may not provide an accurate representation of a material’s effectiveness in reducing low-frequency noise.

Therefore, it is crucial to consider additional factors and alternative solutions when addressing low-frequency noise issues.

Alternative Solutions for Low-Frequency Noise

To effectively address low-frequency noise, alternative solutions such as soundproofing foam or acoustic panels should be considered.

These materials can absorb and block sound waves at lower frequencies, providing more effective sound energy insulation for bass sounds and loud conversations.

By incorporating these alternative solutions into your construction project, you can create a more comfortable environment that effectively reduces low-frequency noise.

Summary

In conclusion, understanding and applying STC is essential for creating comfortable living, working, and learning environments by reducing sound pressure levels and improving acoustic comfort.

By considering factors such as material properties, construction techniques, and room acoustics, you can make informed decisions when selecting materials and designing spaces that offer the desired level of soundproofing.

Although STC has limitations, especially when addressing low-frequency noise, alternative solutions such as acoustic panels can help create a more comfortable environment for occupants. Embrace the power of STC and take control of your acoustic environment today.

Frequently Asked Questions

What is a good STC rating?

A good STC rating is one that rates over 50, indicating how much sound transmission is being reduced. A higher rating indicates even greater effectiveness at blocking out unwanted noise. Ideally, an STC rating of 55 or higher is recommended for maximum sound control.

What is the STC rating of 5/8 drywall?

The Sound Transmission Class (STC) rating of 5/8” drywall mounted with standard 2″x4″ studs is 33 and a staggered wood stud wall is 48, providing excellent noise control.

What does STC 60 mean?

STC 60 is a rating on the Sound Transmission Class (STC) scale, which measures the degree of sound control in a building. It is considered excellent sound insulation and indicates that loud speech is practically inaudible and music can be heard only faintly.

What is STC 50 rating?

STC 50 is an excellent rating for sound transmission loss between rooms, as it means that conversation would be difficult to hear from one room to another and would not be distracting or disruptive. This rating is important for any home or office space, as it ensures that conversations and other noises are kept to a minimum and that everyone can work or relax in peace.

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