The URL can be used to link to this page

Home My WebLink AboutCLE201800087 Certified Engineer's Report 2018-07-02��}11►ACENTECH July 2, 2018 Tyler Gifford Martin Horn 210 Carlton Road Charlottesville, VA 22902 tyler@martinhorn.com Subject Sound Isolation Recommendations Willow River Vet Office, Mill Creek, Charlottesville, VA Acentech Project No. P630195 Dear Mr. Gifford: 2150 Wise Street #4875 Charlottesville, VA 22905 434 218 0759 acentech.com Following our previous discussions, I understand you require recommendations as to the demising construction of the Willow River Veterinary office you're building out in Mill Creek. You have relayed that the county is requesting that the construction meet STC 55. This letter aims to provide recommendations for the interior wall, exterior wall, and ceiling/roof that should meet that requirement. BACKGROUND The standard laboratory metric for partition transmission loss is Sound Transmission Class (STC). Note that STC ratings are conducted in controlled laboratory environments and partition performance in an actual assembly is generally lower due to flanking paths. Should you need to verify performance after construction we are available to measure the Noise Isolation Class (NIC) of the partition, which is a field tested metric for determining how well a partition is perceived to be performing. The standard laboratory metric for ceiling transmission loss is Ceiling Attenuation Class (CAC). The CAC rating is analogous to STC for partitions, but rates a ceiling assembly's sound isolation performance in adjacent rooms with wall partitions that do not extend to the deck above. RECOMMENDATIONS Interior Demising Wall These walls represent the largest path of sound transmission between adjacent tenants. The current construction appears to include 1 layer of 5/8" GWB to the ceiling, 1 layer of 5/8" GWB to the roof deck, 6" steel studs, 3.5" batt insulation, and 1 layer of 5/8" GWB. We estimate this current construction should have a STC rating near 50. We recommend that you construct a secondary wall inboard of the existing demising wall. All openings (including where electrical boxes existed) in the existing wall should be patched and sealed. Construct the new wall with 2" or larger metal studs spaced 1" away from the existing wall, for a total cavity depth of at least 3". Avoid rigid tiebacks between the new and exterior walls. Install at least one layer of GWB on the face of the new studs and 2"+ batt insulation in the new stud cavity. Extend the new walls to the roof deck, and seal their perimeter and any penetrations airtight with an acoustical sealant similar to USG Sheetrock Acoustical Sealant. We expect this completed partition to have a STC rating in the upper 50's. Exterior Wall The current exterior wall construction appears to include 1 layer of brick, 1 layer of CMU, a 7/8" drywall furring channel, and one layer of 5/8" GWB. What we do not currently know is if there is insulation in the acoustics I av/it/security I vibration Tyler Gifford Martin Horn July 2, 2018 Page 2of2 cavity between the GWB and the CMU. We estimate this current construction should have a STC rating near 50 without insulation and near 60 with insulation. We recommend that you determine if insulation exists in the current exterior wall construction. If it does not exist you can attempt to blow cellulose into the cavities and patch the holes. If you do end up removing the GWB, be sure to maintain at least the 7/8" deep cavity between the GWB and CMU, deeper is better, and you must include the batt or blown insulation in that cavity. As mentioned above, we expect this construction to be near STC 60. Interior Walls All interior walls should extend to the roof deck to avoid using the plenum as a transmission path between rooms. Ceiling tiles with a high CAC rating can help control some of that flanking if it isn't possible to extend the interior walls to the roof deck. Note that without a full height wall the total sound isolation performance will be only as good as the lower performing assembly (ceiling path or partition path). I can provide more information on interior wall assemblies upon request. Ceiling and Roof The existing roof structure you have relayed to me includes a corrugated steel roof deck, insulation, rubber roofing, and gravel. This construction should have a STC rating in the mid to high 40s. The drop ceiling will also increase the performance of the roof because the existing plenum cavity is quite large, on the order of 4 feet. To aid in blocking sound from entering the plenum space you should use an acoustical ceiling tile with a high CAC rating (30+) and a layer of batt insulation. A lightweight roof deck can be a significant flanking path. The best process to avoid that possible flanking path is to reduce the sound before it arrives there. This includes decoupling the roof from the room and from any gypsum board walls where possible. Ceiling tiles with high CAC ratings are generally made from mineral fiber (aka rockwool), such as the Armstrong Ultima and Rockfon Sonar. In summary, we recommend using a ceiling construction with a high CAC ceiling tile (>30), with roughly 4ft of plenum space to the roof deck, using 6"+ batt insulation. We expect the total assembly of the roof, plenum, and ceiling to be in excess of the required STC 55 rating. Note that you should also decouple the walls from the roof deck by holding back the gypsum and studs a small amount (-1/4") and fill with acoustical sealant. We are available to provide further analysis, guidelines, or recommendations if desired. I hope this report provides you with the information you need at this time. If you have any questions, please feel free to contact me at 434-218-0759. Sincerely, Acentech Incorporated Bill Yoder Senior Staff Scientist 4>);I;f�► AC E N T E C H