STC and SECUROCK® Roof Boards: Do You Hear What I Hear?

Concerns about building occupants’ comfort continues to grow from both an owner and regulator standpoint. One major concern is how to manage sound in our living and work spaces.

In the past, a building’s sound issues were tackled from the interior looking at walls and ceilings. Now, there is a continued focus on the exterior of a building with a desire to create systems that can better handle outdoor environments (air traffic, highway traffic, etc.) and sensitive buildings (hospitals, schools, etc.) in a more effective way. In this post, we will provide an overview of Sound Transmission Class (STC), how it is measured and tested, several ways to increase STC, and finally how SECUROCK® Roof Boards help create better environments for STC.

STC is the most common sound isolation standard used today and is for airborne noise (unwanted sound). Typically measured in dB (decibels), the higher the STC number the better that system is for blocking airborne noise. One thing to remember, dB’s are a logarithmic unit and displayed on a logarithmic scale, therefore, going from 40dB to 50dB isn’t a 125% increase in perceived sound it actually means the perceived sound is twice as loud. The measurement is over a frequency range of 125-4000 Hz (Hertz) and uses transmission loss to calculate what the STC is. So, STC isn’t necessarily what a system (wall, ceiling, roof, etc.) will stop, but more closely related to a ranking of how well a system can prevent sound transmission. Since STC ignores low frequencies, it also has major limitations in real world applications for areas that are indicated above (for example air traffic has a lot of low frequency noise that is missed by STC). Despite its limitations, STC is an easy number to use and allows agencies and companies to gather data on systems in order to help solve some of a building’s concern around sound.

Testing for STC is typically done by third party laboratories that have trained acousticians.  There are several standards for measuring STC, but the most popular ones are ASTM E90-09 (Standard Test Method for Laboratory Measurement of Airborne Sound Transmission Loss of Building Partitions and Elements) and E413-10 (Classification for Rating Sound Insulation). These ASTM standards create a method for testing airborne sound transmission loss in partitions and obtaining a single number rating called STC.  There is a lot that goes into the actual testing of the partitions, but the general idea is as follows:

• A partition is constructed between two rooms in a laboratory setting.
• While noise is played on one side of the wall, the sound levels over the frequency range of 125-4000 Hz are measured on both sides of that partition.
• The transmission loss of the system is calculated from the difference between the sound levels in the two rooms.
• STC is calculated for that partition based on the transmission loss data collected.

Now that we know what STC is and how it is measured, there are some things to think about in real world applications that might be able to help improve airborne sound transmission. There are several ways to increase the STC rating of a roof/ceiling assembly including adding mass, adding air space, adding absorptive material and decoupling. First, adding mass to a roof/ceiling assembly can have a big effect on blocking sound and this is typically done by adding layers of material such as SECUROCK® Gypsum-Fiber Roof Board.  Second, adding air space within the partition increases the STC. The increasing air space between ceiling tile and a roof deck increases the STC more than having ceiling tile directly under the roof deck.  Third, using an absorptive material like specialized ceiling tile or increase insulation will help increase STC. Finally, decoupling is a mechanical solution that separates layers of the roof/ceiling assembly making it difficult for sound to pass. This typically means using sound clips which USG also manufactures and sells. There are many tricks to increase the STC rating of a roof/ceiling assembly, but remember that everything from the top of the roof membrane to the bottom of the ceiling tile must be considered in order to get the best system.

Lastly, we want to share how SECUROCK® Roof Boards are helping out with this complex issue of building exteriors. We recently did testing at Riverbank Acoustical Laboratories in Geneva, IL to understand some of the effects that STC has with roofing. We took typical roof assemblies and then trialed different configurations. Here are some things we discovered:

• Adding roof boards increased the system STC incrementally
• Glass-Mat and Gypsum-Fiber provided similar results for STC
• The type of insulation does have an effect on STC
• Mechanically attachment and fully adhered systems provided similar results for STC testing

Below is a typical roof assembly that we tested and achieved a STC rating of 41. This assembly had an EPDM membrane, 5/8” SECUROCK® Gypsum-Fiber cover board, two layers of 2” insulation, 5/8” SECUROCK® Gypsum-Fiber thermal barrier, and a 22 gauge steel deck.  We evaluated various construction details of a roof assembly to evaluate their effects on STC rating.

We want everyone to understand that although a roof board adds to the STC rating, the main job of a roof board is to help protect everything below it as well as extend the life of that roof. While a roof board will contribute to the STC of a roof/ceiling assembly, a better reason to choose it is to maintain that STC rating throughout the roof’s useful life.

Please contact your SECUROCK® Roofing Solutions Team for more information and advice regarding your next installation.

Demo the Difference: SECUROCK vs. the Competition

We put SECUROCK head-to-head up against the competition in a 4-part “Demo the Difference” video series. In these side-by-side tests, we compared:

1.  Adhesive Absorption
2.  Cutting
3.  Itchiness
4.  ⅜” SECUROCK Gypsum-Fiber vs. Competitive ½” Glass Mat Roof Board

Watch below to see how our roof boards stack up to the competition!

Adhesive Absorption
First up in our series is a side-by-side adhesive test. This video demonstrates how SECUROCK Gypsum-Fiber will save you both time and money over competitive glass mat products. SECUROCK Gypsum-Fiber has a smooth surface with no glass fibers that will make it easier to roll and push the adhesive quickly across the panel, but ultimately uses less adhesive which will significantly decrease the installation cost. Glass mat products soak up adhesive and ultimately use more than is necessary to properly adhere to. Plus, if you use a glass mat product in adhered systems, you are relying on the bond of that mat to the core, which is why we recommend using products that don’t have a facer for adhered systems. Overall, a better quality system, lower installation cost, and easier to use.

Cutting

In this side-by-side cutting test, you’ll see how SECUROCK Gypsum-Fiber is easier to cut and will leave you with less debris over the competition.  Because it has no facer and is a homogeneous product, all you have to do is score it on one side and snap.

Itchiness

Next up in the “Demo the Difference” series, this video will show you how SECUROCK Roof Boards create less itch when handling.  Because SECUROCK Gypsum-Fiber and SECUROCK Cement Roof Board have no fiberglass in them, it is easy to see why people handling these products don’t have to worry about itchiness.  However, even our SECUROCK Glass-Mat has the same effect because of the high quality mat that we use. This high quality mat means there will be less fibers shedding while it is being moved around. Plus, the higher quality mat gives you a better mat-to-core bond, making it less likely to delaminate when cutting or on the roof than other competitive glass mat roof boards.

⅜” SECUROCK Gypsum Fiber vs. ½” Competitive Glass Mat Roof Board

Last but not least in our series, this video compares ⅜” SECUROCK Gypsum-Fiber Roof Board to a competitive ½” glass mat roof board in regards to weight per panel, compressive strength, flute span, perm rating and moisture rating. Employing advanced technology in delivering an exceptionally strong, sustainable roof board, SECUROCK Gypsum-Fiber roof boards exceed the competition and promises excellent performance in a variety of applications.  So, if you are using ½” glass mat products, chances are that you can use a ⅜” SECUROCK Gypsum-Fiber Roof Board instead and get better performance with a cost savings.

As a leader in the building materials industry for over 100 years, USG is proud to deliver a portfolio of high-quality and high-performing products that give roofing professionals a better choice in the roof board category. All of this adds up to a roof board portfolio that goes above and beyond to meet the needs of any application.

See more videos from SECUROCK Roofing including how-to’s and testimonials at http://www.youtube.com/usgcorporation. To learn more about SECUROCK Roof Boards, please visit http://www.usg.com/securock.

Wind Uplift Explained

Whether for life safety, insurance, or code compliance, wind uplift is a major concern for anyone who manufactures, designs or installs roofing products. In this post, we will provide an overview  of the design process, the two major testing agencies, and how Securock Roof Boards can help you protect against wind uplift in your next project.

When wind hits a building, pressure is exerted against the building as the air pushes against the sides and moves up and around the building.  Wind uplift is a force (pounds per square foot) that occurs when the pressure below a roof is greater than above it. This can happen from many different ways but is usually because pressure above the roof system decreases by high air flow (wind) or pressure increases inside a building from air pressure buildup. When wind uplift is greater than the system was designed for, the roof could potentially lift off the building.

There are many design considerations, but most codes (such as IBC 2012) and design professionals are using the 2010 edition of ASCE 7, or ASCE 7-10 to design a roof system (ASCE is the American Society of Civil Engineers). The old version of ASCE was ASCE 7-05, and with the new version of ASCE 7-10, some things remain the same with the new version, such as factors for design including building location, height and ground surface. However, with the new code, there have also been items that have changed such as the use of new wind speed maps based on risk categories and an expanded seismic area. In addition, there are tools such as www.roofwinddesigner.com that can help with the design.

Once a design professional understands the wind loads on the building, it is time to pick a roof system. For a rated system, most entities (such as IBC 2012) will look to Factory Mutual (FM) or Underwriter’s Laboratories (UL)  for guidance. Because there are differences in how the systems are tested, designers should always compare products using the same test agency numbers.

FM is the default testing standard for wind uplift. Roof assemblies that have been tested can be found on FM’s website. You should know that the testing is based on assemblies, not components. The two main FM  testing standards are FM 4450 and FM 4470.

1. FM 4450 tests Class 1 insulated metal decks.
2. FM 4470 tests all other Class 1 roof covers.

With FM Tests, the roof system is pressurized from below the deck to 30 psf, and held for one minute.  The pressure is increased by 15 psf increments every minute until failure.

UL has two standards for testing wind loads: UL 580 and UL 1897.  You may notice there is no safety factor in the UL numbers. The test is in pounds per square foot.  This is not a design number, but a test number.

1. UL 580 is a dynamic pressure test.  In addition to pressure from below, UL 580 draws a vacuum on top of the membrane. Pressure levels are varied throughout the duration of the test.
2. UL 1897 is a static pressure test in which an apparatus that creates a steady negative pressure is placed on the top side of the membrane.  Pressure is held for one minute and raised by 15 psf increments, until failure.

Wind uplift is a force that occurs when the pressure below a roof is greater than above it, and if the wind uplift is greater than the design of a roof system, it can blow the roof off the building. Design professionals will typically use ASCE 7-10 to find the proper wind load of a building.  Once that design parameter is found, the default testing agencies are FM (4450, 4470) and UL (580, 1897). Properly tested products that meet the design criteria, such as Securock High Performance Roof Boards, will help ensure that a safe building is constructed.
Now, we would like to give you some understanding of where Securock Roof Boards can potentially rate for FM testing.

Finally, using the very common FM 1-90 rating with a typical assembly (TPO adhered to a cover board that is mechanically fastened onto a metal deck), it is easy to see how costs can add up depending on the roof board that you select.  Below is a table of different roof boards for this assembly.  We assumed $.20 / fastener (screw and plate), average roof was 100’ x 200’ (625 4’x8’ roof boards), and it took an average of 2 minutes to screw in a fastener with a labor rate of $20/hour.

As you can see, using Securock Gypsum-Fiber on a 20,000 square foot job can save you as much as $4,333 just in fasteners and labor.  So, not only will you get a great product that will be easier to install, enhance the safety of your client’s building, and is made from 95% recycled material, you will also save money on installation.

Introducing USG’s “Building A Better System With Roof Boards” CEU

Learn how to create an overall better system with roof boards and receive 1 AIA HSW CEH credit in USG’s new Roofing CEU on the Hanley Wood University! Architects, designers and other participants will learn the importance of roof boards and how to create a better roofing system with the use of the most highly-rated types of roof board.

Although the installation cost of a roof is generally less than 4% of the overall cost of the structure, an estimated 60-70% of all construction litigation is roofing. To help reduce the amount of failed roofs on commercial buildings, and to cut down on subsequent litigation, this course is focused on learning about and creating an overall better roofing system.

This course will provide an introduction to roof boards and what they do in various applications, along with information on some of the forces that can negatively impact roofs such as fire, wind, impact, mold, moisture and foot traffic. Participants will learn how the impact of these forces can be measured and reduced. Learning objectives for this course also include listing the different types of roof boards and their attributes, as well as discussing the importance of specifying roof boards in a roof system.

Along with a wide range of other courses, this course can be found on Hanley Wood’s University here: Building a Better System with Roof Boards. All courses at HanleyWoodUniversity.com are free and can be accessed at your convenience 24 hours a day, seven days a week, 365 days a year.

We are pleased to provide this important educational service to the industry and welcome your thoughts and comments on the course here.

Sustainable Roofing System Featured on One of the Nation’s Greenest Park-based Buildings

For sustainability in architecture and construction, the roof is sometimes overlooked, but sustainable roofing materials are increasingly being viewed as a viable solution. USG Securock® gypsum-fiber roof board, made from 95 percent recycled content, has become a preferred material for sustainable roofing systems and has been awarded a Green Cross certification from Scientific Certification Systems.

One of the more recent sustainable projects using USG SECUROCK gypsum-fiber roof board is the Golden Gate National Parks’ Crissy Field Center. The Crissy Field Center is an award-winning environmental education facility, operated in partnership by the Golden Gate National Parks Conservancy, the National Park Service, and the Presidio Trust. The high performance modular facility, currently on track for the US Green Building Council LEED® Gold Certification, serves not only as a hub of sustainability programming in the Golden Gate National Recreation Area, but also as a convening spot and resource for local community organizations, visiting diplomats, politicians, and educational leaders on both national and international fronts.

The project’s 10,000 square-foot sustainable roof system features an assembly of environmentally friendly building materials including USG SECUROCK gypsum-fiber roof board. Since the Crissy Field Center is in immediate proximity of saltwater (San Francisco Bay), one of the harshest environments for building products, it was important that the roofing materials be moisture resistant. USG SECUROCK’s gypsum-fiber roof board has been treated for uniform moisture resistance throughout the panel. In addition, in testing it scores a 10, the highest score for mold resistance, on ASTM D3273.

After the Crissy Field Center moves back to its original location, the interim building will be re-used and possibly relocated and reused. In the meantime, the Center is open and has integrated its current building’s green technologies and sustainable design into its programming, including sustainable development workshops and site tours.

Learn more about the Crissy Field project (PDF) and the Crissy Field Center in San Francisco.

We would love to know about any other sustainable building projects or products you’ve heard about. Please share your thoughts below.