Acoustical Performance Steel Building Insulation
Insulation for steel buildings is used primarily to keep the indoor temperature comfortable for the occupants. A metal structure that is thermally efficient provides savings in energy costs. An additional benefit of insulation is that it prevents the transmission of noise into and out of the building, and at the same time, inhibits the echoing of indoor noise within the building.
Metal building insulation is made of porous materials, making it an excellent absorber of sounds of up to 5-6 dB. This same property reduces the amount of sound that is transmitted through the building’s walls and roof. Occupants of the steel building will have a quieter working environment, while neighbors will not complain of noise produced by machines or equipments, if any, operating inside the building.
Sound Absorption Coefficient
Sound absorption coefficient is the measure used to indicate how good a material is in absorbing sound. The standard range of this measurement is from 0.05 to 1.20. A high sound absorption coefficient is desired. However, this coefficient is measured at several frequencies. For instance, a material’s sound absorption coefficient of 0.75 at a particular frequency, simply means that 75% of the sound that strikes that material is absorbed. To put it another way, it means that 25% of the sound is echoed back into the room. The range of sound absorption coefficients for steel buildings is from 0.20 to 1.20.
Noise Reduction Coefficient (NRC)
The ability of a material to absorb sound at multiple frequencies is expressed in a single number rating called noise reduction coefficient. Again, a high NRC value is desired. The range of NRC values of faced insulation for steel buildings range from 0.75 to 0.90.
Sound Transmission Loss
As stated above, insulation lessens the transmission of sound from the outside to the inside of the building. There is a measurement of this ability of walls and roof to reduce the amount of sound transmitted and its called sound transmission loss which is expressed in decibels (dB). However, it is also measured at varying frequencies. The tightness of the steel building’s walls and roof cannot be overemphasized. Gaps produce air and sound leaks and reduce the effectiveness of the insulation, Fill gaps with sealants such as non-curing Butyl, siliconized acrylic latex, or acrylic latex.
Sound Transmission Class (STC)
Sound transmission class is used to represent a single number rating, of a material’s sound transmission loss properties for various frequencies. Like all the other measurements, a high STC value is desired. The typical STC values for steel buildings range from 20 to 55.
Outdoor-Indoor Transmission Class (OITC)
A new single number rating has recently been introduced - the outdoor-indoor transmission class or OITC. It is a measure of the sound transmission loss properties of the building’s exterior walls and roof. To calculate the OITC value, the outside noise coming from vehicular traffic, aircraft, and trains is used. The OITC is the preferred rating for exterior walls and roof, of steel building owners.