Weather Membrane Barriers

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Author Message Dewayne Dean Senior Member Username: ddean Post Number: 99 Registered: 02-2016 Posted on Thursday, November 10, 2016 - 05:39 pm:    Just wondering how you all handle the various types of membrane barriers ie. permeable, impermeable, self adhered, mechanically attached, fluid applied. Do you have separate sections or one section with all types? Thanks in advance Steven Bruneel, AIA, CSI-CDT, LEED-AP, EDAC Senior Member Username: redseca2 Post Number: 562 Registered: 12-2006 Posted on Thursday, November 10, 2016 - 07:13 pm:    My default approach for a project with a rain screen assembly including a cladding system and continuous insulation over the sheathing is to include two separate Sections for "Fluid-Applied" and "Self-Adhering" products. These Sections share the same manufacturers and general format. For a design/bid/build project the Contractor is supposed to select and use one. For design/build and its many variations we usually resolve which to use before construction begins, often through pricing them as Alternates. Organizing these sorts of options is getting trickier now with the marketing of mat-faced gypsum board "systems" that only need the joints and penetrations sealed with a proprietary sealant. We have not executed a project using this approach but I have prepared a stand alone Section that replaces the above air/water barrier Sections as well as the Gypsum Sheathing Section if it is implemented. Edward J Dueppen, RA, CSI, CCS, LEED AP Senior Member Username: edueppen Post Number: 31 Registered: 08-2013 Posted on Friday, November 11, 2016 - 09:46 am:    Dewayne, I keep separate sections for different types of air barriers, generally based upon application method (e.g. sheet, fluid, mechanically fastened). But I list vapor-impermeable and vapor-retarding within the same sections. In the few odd occasions when I have a project with both permeable and retarding, or more than one application method, I develop a designation with the team to identify them as "AB1", "AB2", etc. so that it is evident on the Drawings and in the specs which is which. Dewayne Dean Senior Member Username: ddean Post Number: 100 Registered: 02-2016 Posted on Friday, November 11, 2016 - 10:07 am:    Thanks guys RH (Hank) Sweers II RA CSI CCS Senior Member Username: rhsweers2 Post Number: 16 Registered: 08-2005 Posted on Friday, November 11, 2016 - 10:46 am:    Not to throw a wrench into this, but from various continuing ed seminars I have attended and actually remembered a bit of, the sheating itself constitutes an "air barrier", so I specify a "water resistive barrier (WRB)" system and make sure the drawings show it applied to the exterior face of the sheathing (usually as a heavy, dashed line on the sheathing surface). I can change the type of WRB through the spec used (fluid, self-adhered sheet, or even sheet membrane if forced to do so), and have had alternates listed for use of self-adhered membrane if cold-weather limits application of the base spec fluid-applied system. Originally, I used the term "weather resistant barrier" as also used within the building code (I believe), but one of the seminars said that it is really a "water resistive" barrier, since it's inside the weather-resistive cladding. As to sheathing with integral WRB, I've actually created a separate "sheathing" section including this, more to indicate that it's not your father's sheathing material. Otherwise, the WRB aspect may never be noticed - though that shouldn't be my concern as long as it is clearly indicated therein. What I have concerns with are how to assimilate all of the various flexible and through-wall flashings that are often a part of the perimeter and joint sealing component of a WRB system. Right now, I have through-wall sheet metal in the typical sheet-metal spec. I also have a "flexible flashing" spec more attuned to WRB systems behind rain-screen wall panels. But it seems they should really be a part of the WRB system spec - not separate sections. I may have this over-specified right now, but that's probably better than never specifying it at all . . . So does .018 inch thick (26 gage) stainless stell continue to be included within the Sheet Metal Flashing and Trim Section, or move to the WRB system spec? Any clarity from the experts is appreciated!