The Effects Metal Roofs have on Building Acoustics in Schools
Over the past few decades, research has been conducted that indicates building acoustics directly impacts overall student academic performance as well as vocal health of educators.[i] The research led to the new “Standard for Classroom Acoustics” (ANSI S12.60) and has improved the learning environment for students and the work environment for educators. The LEED for Schools Program gives credits to school buildings that have adopted these new standards. However, schools built prior to 2003 may not have an adequate acoustic environment- especially schools with un-insulated or poorly insulated metal roofing systems.
Why is building acoustics so important? According to James D. Janning, AIA, CSI for USG Corporation, “In today’s architectural environment, good acoustical design isn’t a luxury- it’s a necessity. Acoustics impacts everything from employee productivity in office settings to performance quality in auditoriums to market value of apartments, condominiums, and single-family homes.”[ii]
Sounds from outside the building envelope can greatly affect the internal building acoustics. Road noise, airplanes, factories and weather will effect overall building acoustics. The building envelope materials can either reduce this sound invasion or not. In some cases building material can even amplify it. For example, concreate is an excellent soundproofing material whereas metal is not and in some case can amplify it. [iii]
To understand how metal roofs affect building acoustics we must first look at what sound is. Sound is a vibration into an elastic medium- air, water, or physical material. This medium is elastic because it returns to its normal state after being influenced by sound vibration. The more elastic the substance the better it is at conducting sound waves. Metal roofs are highly elastic and can even amplify the sound vibrations with increased energy (e.g. energy produce by a falling mass like rain or hail). [iv]
The noise level that is comfortable to humans is between 55-60db. A Metal roof is a conduit for external sound waves and thus a poorly insulated metal roof will decrease the acoustic quality in a building even if the remaining envelope (walls, windows, doors, and ceiling void) is made of material that reduces it.
For example, there is a school envelope in which the outer walls are made of concrete, windows are double pane, and doors are solid oak. These materials are great at soundproofing because they have reduced or no elastic properties and deflect sound waves. Unfortunately, this building has a poorly insulated metal roof. Noise produced by rain on metal roofs can exceed 70 db.[v] Now imagine these sound waves bouncing off the internal envelope (like a drum) while students try to learn. This type of environment led to the development of suspended ceilings as a means of creating a soundproof void between the human space and the roof. The downside of this is the reduction of usable space- as well as open space- within a building envelope.
On a pitch metal roof in one study, a heavy rain fall produced an internal sound of 85-90 db. On a flat and pitched metal roof in this same study, the sound level almost reached 100 db. Furthermore, the researchers asked users of the buildings studied the affect rain noise had on them. “52% of respondents agreed that one of the main causes of the noise is from the roof and 48% of them agreed that rain will hinder their movement…. 75 % percent agreed that rain noise affects their work and study.” The results of this study “shows that sound generated by rain drop on metal deck roof profiles contribute to acoustic problems to a building and produce a negative effect in people lives during rain, in terms of psychological and communication problems.[vi]
There is a solution that will not only insulate a metal roof from external noise, but can give a school a whole new roofing system. This method will increase the acoustic properties, increase R-value of the building that saves money, and aesthetically give the building a new updated look.
Retrofit systems over existing metal roofs can be a great alternative. In a retrofit system the original metal roof becomes the deck of the new roofing system. This not only allows building use to continue during the process but reduces landfill waste from a full tear off. Retrofit systems is a way for an organization to continue to be green committed.
Retrofit systems also add insulation to an uninsulated or poorly insulated metal roof system. This added energy saving feature is not only environmentally friendly but reduces energy costs year round. Moreover, having a TPO or PVC membrane installed can give the structure a new lasting look compared to existing metal roofs which can looked weathered over time even with coating.
[i] Acoustics of Schools : a design guide, November 2015: Institute of Acoustics & Acoustics and Noise Consultants.
[ii] James D. Manning: Understanding Acoustics in Architectural Design. AIA/Architectural Record Continuing Education Series.
[iii] K.B. Ginn, M. Sc. : Architectural Acoustics, 1978- Bruel & Kjaer:
[iv] James D. Manning: Understanding Acoustics in Architectural Design. AIA/Architectural Record Continuing Education Series.
[v] Muhammed Fahmi MD Idris, Mohd Muzani Musa * Seti Mariam Ayob: Noise Generated by Raindrop on Metal Deck Roof Profiles: It’s Effect towards People Activities. 2012 – Procedia: Social and Behavioral Sciences.
[vi] Muhammed Fahmi MD Idris, Mohd Muzani Musa * Seti Mariam Ayob: Noise Generated by Raindrop on Metal Deck Roof Profiles: It’s Effect towards People Activities. 2012 – Procedia: Social and Behavioral Sciences.