This is a followup and additional question to my June 7, 2011 post.
On 8/1/2011 a LEED Interpretation was posted for IEQc9: Enhanced Acoustical Performance (ID Number: 10095). It basically says that the use of the 2010 version of ANSI S12.60 is acceptable for LEED for Schools 2007 and 2009.
In ANSI S12.60-2010 Table 4 there is a footnote (b) that says “A 20cm (8”) concrete masonry unit wall having a surface weight density of at least 180 kg/m2 painted and sealed on both sides, acoustically sealed at the entire perimeter and extending from the floor slab to the structural deck above, is an acceptable alternate assembly that conforms to the intent of 5.4.2.1.” This could impact us greatly, because we had to issue an addenda to add Perlite or foam-in-insulation to our 8” CMU walls between classrooms to mee the STC 50 rating between core learning spaces. It seems that according to this footnote, this would not be required, which would could have a big dollar cost savings. I believe we are meeting all the requirements of the footnote, but I am not sure about the “surface weight density of at least 180kg/m2” part. I’ve researched and asked masonry and paint technical reps, but no one seems to understand what this means.
Has anyone heard of this or had any experience with it? I want to ensure we are meeting all the requirements of the exception before we tell the client we no longer need Perlite/foam-in-insulation.
Daniel Hicks
Daniel Hicks, E.I., INCEGeiler & Associates
267 thumbs up
October 10, 2011 - 11:14 am
The mass of the block you are using will determine the amount of sound isolation that the block will provide. Light blocks will perform worse than normal weight concrete, if that makes sense.
The surface weight density is a way to specify the mass of the block without knowing one of the dimensions. 180 kg/m2 is approximately 36.8 lb/ft2.
With the block you are using, take it's weight (lb) and divide by the face area of the block (ft2). If it is 36.8 or higher, you're in luck. If not, you'll have to use the insulation, or increase the thickness of the block to obtain a higher overall mass (if that's an option).
Rebecca Griffith
65 thumbs up
October 10, 2011 - 11:31 am
Thank you, Daniel! That is a very clear explanation and just the clarification we needed to figure this out! Much appreciated!