b'T&R Update1.Use of a vapor retarder between the roof system and theLWSC and RWSC. concrete roof deck is highly recommended. It need not necessarily be an adhered vapor retarder. SuccessfulA note on ASTM F-2170. The NRCA has stated that 75% RH installations over LWSC have been made with ballastedshould be a safe number for application of a roof system over systems and Inverted Roofing Membrane Assembliesa concrete deck. The origin of that number is in the Portland with a loose laid vapor retarders.Cement Association Bulletin D141 from 1968. In that bulletin 2.Extreme care must be taken in installing the vaporthey assess the moisture content (RH) of RWSC and LWSC in retarder, wither adhered or loose laid. Even small holes,a laboratory environment. After 30 days the upper portion of fish mouths or other breaches in the vapor retarderthe RWSC had gone below 75% RH. We have for decades placed can lead to long term moisture migration into the roofroofs over RWSC after 28 days of field curing. It was therefore system.hypothesized that 75% was a safe moisture level to apply a roof 3.Edge details and penetration details must includesystem over concrete. NOTE: To date there is no experimental detailing of the vapor retarder.or field data to confirm OR deny this number. Therefore until 4.Directly contact the technical department of the roofa consensus is reached the 75% RH safe level put forth by the membrane manufacturer. As every manufacturerNRCA should be heeded. However it must be conceded that in currently has their own position on LWSC, get theirssome environments 75% RH may not be achievable with any in writing. If moisture problems do occur a solid paperreasonable amount of dry time, if ever.trail is a good insurance policy.As always if MRCA members has specific technical concerns 5.Provide the general contractor and architect the MRCA,or issues please bring them to our attention. We are always NRCA and SPRI advisories, plus the written position ofstriving to serve the technical needs of MRCA members, and the membrane manufacturer. If the manufacturer willthe roofing industry on current issues. But we need your help not warrant the design, it should not be the contractorsto notify us of these issues. responsibility to correct the design. 6.Consider using a metric to determine when the LWSCMatt Dupuis, PhD PE, of SRI in Middleton, WI, can be reached roof deck is ready for roofing and or application of aat MDupuis@sri-engineering.com. Dupuis serves on MRCAs vapor retarder. Surface readings of moisture contentTechnical and Research Committee.with meters or tests using calcium chloride are not reliable. Consider the use of ASTM F-2170 as a metric. It was designed for use in concrete floors but can be relied upon to produce readings for concrete roof decks; both PLACES TO FIND TALENT TO DIVERSIFY THE LEADERSHIP RANKSMost Colleges and Universities have programs that targetDartmouth Collegestudents that historically (African American, Hispanic,http://dartmouth.edu/dartmouth-glanceAppalachian)that are first generation, have not attended34% minority students at the Ivy League level-See diversitycollege or graduated from college. These programs are a great place to find interns that can grow and understandNational Black MBA Associationyour business while in college. Exposure to commercialhttp://www.nbmbaa.org/aboutus/boardofDirectors.aspxroofing is the key to success. Most people of color, are notGP has a Board Member to this organization exposed to our industry. http://www.nbmbaa.org/partners/Default.aspxCorporate Partners-all of which we would like to haveTop colleges to find diverse students business with!http://diverseeducation.com/article/53530/Colleges for African American Engineershttp://www.bestcollegesforblacks.com/ENGINEERING.htmlLatinos in Construction Facts and Figures For more information contact: ByronStallworthhttp://www.nclr.orgStrategic AccountManager at NATIONAL ROOFING PARTNERS.search EmploymentReportAugust2013.pdf 800. 537.6034or atbryron.stallworth@nationalroofingpartners.comwww.mrca.orgMidwest Roofer 21'