New school designed to meet strict acoustic standards.
When children file into classrooms at newly completed Des Moines Elementary School in Washington state, one thing will be missing: the deafening roar of jet engines landing at nearby Seattle-Tacoma International Airport (SeaTac).
The school replaces a building originally constructed in 1925. To give the elementary school a solid Washington feel, local talent was brought in to design and build the project. Hutteball + Oremus Architecture, Kirkland, WA, designed the new school, with Ingrida Sanders acting as designer and project manager. Absher Construction, Puyallup, WA, was general contractor.
Because the new school lies directly in the flight path of SeaTac, noise mitigation, as it related to the wall and roof assembly, moved to the top of the list of concerns. Products and design needed to be chosen and integrated in such a way that ongoing air traffic wouldn’t disrupt daily learning and Washington’s notoriously rough weather would be kept at bay.
“This is the first time we’d designed a project to meet strict noise standards,” Sanders explained. “All the products we specified for the building envelope, from sheathing to glazing to roof board, had to meet certain Sound Transmission Class (STC) ratings to meet health department administrative code and Federal Aviation Administration (FAA) requirements.”
During the research phase of the design process, Sanders realized that two of the products on which she was focusing were manufactured by the same company: Georgia-Pacific (GP), Atlanta. “The idea of specifying such an envelope was attractive and beneficial for the project in multiple ways. It was nice to have all of the products come from a single manufacturer so we knew they would be compatible. And, it was an easier process during the procurement stage,” she said. GP calls the product mix Dens Solutions.
Since Sanders had specified GP DensDeck Prime roof board on multiple past projects, the decision to incorporate it into the Des Moines building envelope was easy. “It’s suited for weather protection and mold and fire resistance,” she said.
To achieve a Sound Transmission Class rating of 49, three 1/2-in. layers of the roof board were specified to cover the roof’s deck. “Our acoustical consultant recommended we use at least two layers of 5/8 in. roof board, but we decided to use three 1/2-in. layers to ensure the students were protected,” Sanders said.
DensDeck Prime can be used both as a cover board and thermal roof board. Since the district chose to install a temporary roof on the building during the construction process, the first layer was used as a base for a self-adhered waterproof underlayment. “It was helpful that the contractor was able to use the first layer for the permanent roof rather than having to install an additional cover board for the temporary roof,” Sanders noted. “Since they were dealing with wet weather, it allowed them to dry-in the temporary roof more quickly, which helped save the schedule.”
The roof board features EONIC technology, a patented process said to double its resistance to moisture, enabling it to meet a three-part specification for moisture resistance. Elements of that specification include a 5% total water-absorption resistance by weight and 1-gram surface-water absorption performance on both sides of the board. Also notable is the board’s mat-to-core bond strength, which in third-party testing averaged 23% stronger on the face and 192% stronger on the back when compared to DensDeck Prime roof boards before the enhancement, according to the manufacturer.
The dimensional stability of the product, when used as a cover board, eliminates gapping, making them easier to install. Jake Peavler, project manager for Absher Construction, commented, “It’s one less thing we have to take into consideration for our installers and one less thing they have to worry about. That saves time.”
Running a close second to noise abatement on the list of items to address with the wall and roof assembly: weather resistance.
Seattle’s reputation as having ever-changing weather is well deserved. While mostly temperate (highs in winter in the 40s, lows in the 30s; summer highs in the 70s and lows in the 50s), according to some sources it does rain 50% of the time. In the winter, when the temperatures dip below freezing, this equates to snow and ice—items that can create havoc with the building envelope.
When it came to the walls, the goal was to choose a product with a lower drying time and easy installation. The answer was GP’s DensElement barrier system. Said to have a lower drying time than other options (such as fluid applied), the contractor would save time by simply applying Prosoco R-Guard FastFlash on the seams and fasteners.
Integrating three products into one—gypsum sheathing, a water-resistive barrier, and an air barrier—the system uses AquaKor technology to create the WRB-AB (water-resistant board-air barrier) within by integrating the fiberglass mat and gypsum core to form a monolithic, hydrophobic surface that blocks bulk water but allows vapor passage, eliminating the need for a separate WRB-AB.
In recent third-party testing by RDH Building Sciences, with offices in Seattle and other U.S. and Canadian locations, DensElement barrier system is reported to have demonstrated matched performance with that of a fluid-applied WRB-AB when it came to fastener sealability.
“We had internal quality control with the help of the building consultant, so it was an easier process just having to seal the seams and fasteners rather than covering every square foot of sheathing,” Peavler stated.
Once the building envelope was specified, another product popped to the surface and caught the eye of Sanders: GP’s DensShield tile backer. The busiest floors in the new elementary school won’t be those of the cafeteria or even the classrooms—it’s the restrooms. The backer board, with a built-in moisture barrier, was the perfect choice. The acrylic coating surrounding the product provides a built-in moisture barrier that stops moisture at the surface. This protection is what would be needed in a room likely to be covered in water on a daily basis.
The combination of roof board and wall system will create barriers against the weather and air-traffic noise. At the groundbreaking for the new facility, Des Moines Elementary School principal Rick Wilson commented, “We are looking forward to a grand opening when we can welcome students, staff, and families to a modern school building that will serve this community for generations to come.”