Stone Wool Roof Insulation - A Climate Driven Choice
When looking at roof assemblies, the insulation used can make a notable difference in reducing the amount of noise that is transmitted through the roof structure. Engineer John Straube of BSC has addressed this in their work and found that “foam plastic insulations typically used in (low slope) roofs have relatively poor acoustic performance. Stone wool insulation used, even as only part of that low slope roof package can make a dramatic difference in reducing sound transmission. And this has lots of practical value near airports or any other place where lots of sound can come from above.” These comments are based on the fact that the higher density of stone wool insulation compared to other insulation materials means higher acoustical resistance is achieved. Further, the non-directional fiber orientation of the stone wool helps with the absorption of acoustic waves and can reduce the intensity and propagation of noise. These denser structures, coupled with tight, seamless joints create effective barriers to noise and contribute to much quieter and safer work environments. The case studies in this article present two excellent examples of this performance.
Ridgewood High School, Norridge, IL |
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Re-roofing of Ridgewood High School Significantly Reduces Low Frequency Aviation Noise from Chicago O’Hare Airport Although Ridgewood High School has served the Chicago suburb of Norridge for over six decades, the airplane noise only became a problem a few years ago when flight patterns in and out of O’Hare changed. Due to glazing that inadequately isolated sound isolation, the make-up of the original roof assembly and a lack of air conditioning that required open windows in some classrooms, the exterior envelope of the school was incapable of keeping aircraft noise out of the classrooms. “The noise can be so bad the teachers sometimes have to stop in mid-sentence,” said Arturo Benitez of DLA Architects, who is overseeing the Ridgewood High School construction project designed to keep noise from making its way into the classrooms serving Ridgewood’s 900 students. Increased flight volumes at airports across the U.S. prompted the federal government to fund a $220 million project dedicated to helping insulate high-impact facilities against sound interference. Ridgewood qualified because octave band noise testing confirmed that measured noise levels exceeded the 45 dbA maximum acceptable level included in ANSI S 12.60 for schools, LEED® for Schools 2009 and Federal Aviation Administration guidelines for Type 4 buildings (schools). Thus, the school was included in the Chicago Department of Aviation’s School Sound Insulation Program for communities surrounding O’Hare and became eligible for federal sound remediation construction funding to bring decibel levels within FAA guidelines. After considering a variety of options, Benitez and his sound consultant, Laurie Kamper of Threshold Acoustics, determined that a roof assembly that featured alternating layers of exterior gypsum boards and stone wool insulation would achieve the desired sound attenuation levels. The new roof assembly is layered as follows (bottom to top):
Importantly, by changing the materials above the roof deck the interior of the building’s ceiling structure has remained intact, allowing for ongoing construction while classes were in session. The 2011 published results of third party testing of the assembly confirmed that the construction was ideal for the project. It was the first gypsum roof board assembly tested to contribute to Sound Transmission Class (STC) ratings of up to 61 and Outdoor Indoor Transmission Class (OITC) ratings of up to 49 in roofing assemblies for commercial framed construction. The stone wool insulation demonstrates superior sound reduction characteristics as its non-directional fiber orientation helps to trap and dissipate sound waves. The product also has a higher density top layer providing strong point-load resistance and effective load distribution. The product maintains a stable R-value over time, is dimensionally stable and won’t shrink or off-gas blowing agents into the environment. The fiberglass mat gypsum roofing cover board features a combination of fire resistance, strength, dimensional stability and ease of installation. The mass of the gypsum core acts as a barrier to sound transmission and has been tested to show superior sound mitigation properties. Also, both gypsum and stone wool products are non-combustible, providing added fire resistance and safety to the building structure. Combined with other sound remediation enhancements—such as enclosing the rooftop duct system and AV units; adding extensive amounts of stone wool for interior stud walls and roof duct enclosures; adding laminated, tempered glass windows; and installing acoustically-rated door systems in certain areas—the new roof at Ridgewood is already making a significant impact in the classroom. |
Flynn Canada, Etobicoke, Ontario |
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Architect: Geza Tormasi- Associate with Glenn Piotrowski Architect Ltd. Project Timeline: 2010-2011 Project Size: 82,000 square feet Flynn Canada is a trade contractor of complete building envelope solutions. With 17 offices from coast-to-coast they manage single facilities, as well as organizations with national real estate portfolios. When the company needed to expand its own real estate, by turning a warehouse into office space, the noise inside the building from the nearby airport needed to be addressed. A re-roof was needed over the office space portion of the building. Valcoustics, an acoustical consulting company, performed acoustical testing on the building before and after the re-roof to assess the difference in noise transmission frequencies. Insulation solution: A rigid stone wool insulation board with dual density properties was specified based on its higher density top layer providing strong point load resistance and effective load distribution. Further, the stone wool met the project requirements to be fire resistant, water repellent, sound absorbent, sustainable and provide a long term stable R-value. Roof Assembly (top to bottom):
Results: Stone wool insulation was successfully used over existing materials to retrofit the roof for noise reduction. The insulation demonstrates superior sound reduction characteristic and improved low frequently sound absorption to both normal and random incidents of noise. The non-directional structure is denser than traditional insulations which effectively reduces airflow and sound transmissions for excellent sound reduction. According to the sound consultant, “Substantial improvement in the indoor acoustical environment was achieved. Outdoor sound levels due to the aircraft flyovers were reduced by up to 39 dB.” They went on to point out “Based on the same sound level at the roof for the pre and post renovation condition, the indoor NC level has been reduced from NC 61 to NC 39 with the indoor sound level dropping from 58 dBA to 45 dBA. This reduction is a direct result of the roof upgrade, which included the addition of the stone wool 2.5 inch insulation.” Meetings are no longer interrupted by airport traffic noise due to 13 dB noise reduction after re-roof. |
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