Vapor barriers

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Author Message Robin Treston Unregistered guest Posted on Thursday, October 24, 2002 - 10:13 am:    Since I do most of my work in the desert southwest, the question of weather barriers, and/or faced insulation doesn't come up much. I am now doing several projects in colder, snow laden regions, so the issue has arisen. My first and immediate question is - what is the "standard" practice in areas like Utah, Colorado etc. My second question is, does anyone know any good resource(s) that I can use to improve my knowledge and understanding of when wall and roof vapor barriers are recommended. Thanks! John Bunzick, CCS, CCCA New member Username: Bunzick Post Number: 38 Registered: 03-2002 Posted on Thursday, October 24, 2002 - 02:19 pm:    Check out some of the white papers on www.buildingscience.com for some interesting (and some would say controversial) information. There is some thinking that vapor retarders are only needed in more extremely cold climates. Often the building codes require vapor retarders, so you should start there. In cold climates the vapor retarder is on the warm side of the assembly. It is more complicated here in Massachusetts because in addition to a vapor retarder, we must have an air barrier (a very carefully constructed one, I might add.) This is to prevent exfiltration of cold moisture-laden air through the building envelope, where the moisture will condense and cause all kinds of problems. In order to avoid creating a zone where moisture can be trapped between the air barrier and vapor retarder, the best practice has one element performing both functions. This means, for example, a membrane on the sheathing, rigid insulation outside of the sheathing, and no batt insulation within stud cavities. I like this approach, and I think it can work well in any cold climate. The Mass. Board of Building Regulation and Standards has developed some details in conjunction with local consultants. See them at http://www.state.ma.us/bbrs/energy.htm. William C. Pegues, FCSI, CCS New member Username: Wpegues Post Number: 8 Registered: 10-2002 Posted on Saturday, November 02, 2002 - 04:57 pm:    I thought I would post here and see if anyone has encountered any 'mold recommendations' lately. I am in Washington, DC, and due to a rather spectacular failure of a "design build" stormwater piping (that leaked like crazy) and a contractor that did not move to do anything about it right away, mold has grown like crazy in the outer walls, and elsewhere. This was a condo, and occupied, and the condo owners are of course, suing everyone. And now what we have seen are very nervous developers for both high rise apartments and condos seeking recommendations from 'mold experts'. One such recommendation that an owner passed on to us for a building which is brick on metal stud wall (high rise) with sheathing, building wrap and batt insulation with foil facing on the insulation. The mold expert did not want any kind of barrier to the movement of moist air out through the building. Yet, in another statement, wanted a vapor barrier on the cold side - against the sheathing, he wanted no warm side vapor barrier at all. Just thought I would toss that out there since mold issues have come up in other areas, and others might see developers coming up with this kind of expert recommendaiton. Phil Kabza Unregistered guest Posted on Sunday, November 03, 2002 - 08:32 pm:    The National Institute of Standards and Technology (NIST) offers the MOIST software program for analysis of moisture movement through wall and ceiling assemblies. http://www.bfrl.nist.gov/863/moist.html It is referred to in recent ASTM literature as the most practical tool for analysis of condensation control in construction. We're starting to make use of this tool. It does not do a month-by-month analysis of dewpoint conditions, so vapor barrier placement (if any) remains a matter of judgement. The juiciest mold anecdotes I've been hearing derive largely from contractors' failures to prevent water coming into the building after finish materials arrive. William, I get an uneasy feeling about your mold expert above. Sounds like he's from Florida. I'm afraid that ... ah ... ah ... achoooo! ... he's in the mold making business. I'd get the developer to provide a hold harmless letter backed by an insurance policy if he decides he knows better than his design professionals about engineering walls to prevent condensation. William C. Pegues, FCSI, CCS New member Username: Wpegues Post Number: 9 Registered: 10-2002 Posted on Monday, November 04, 2002 - 02:02 am:    Phil, I will have to take a look at that analysis program. Interestingly, the mold expert was from Boston. But, he was a Phd, not sure of his actual construction background. He also wanted to take the brick wall and refer to weeps as vents, put them at the top (under a line of flashing) as well as the bottom (over the line of flashing) and have them at every brick joint as a full vertical joint void, NO weep vent material, no motar collection devices, he wanted to keep the bottom 'propped up' while the wall was built so that the mortar droppings could be continually cleaned out (abuse of the flashing material was not considered, let alone construction technique) and all of that was to make sure that air flow/circulation was maintained in the wall cavity. I thought maybe I should install fans in the cavity to assist -grin! Fortunately, the Owner has instructed us to ignore the letter. John Bunzick, CCS, CCCA New member Username: Bunzick Post Number: 41 Registered: 03-2002 Posted on Monday, November 04, 2002 - 11:11 am:    Providing some ventilation to the brick cavity makes some sense, but maybe not the extreme your consultant has suggested. Putting the vapor retarder on the cold side goes against every recommendation I have seen - at most, some recommend having NO vapor retarder. Maybe this could work, but on the other hand, this would conflict with the desire to construct veneer walls with elements of the rain-screen principle, such as a water-"proof" membrane at the face of the sheathing, with foam insulation outboard of that. Much moisture is introduced into walls by massive air exfiltration (in colder climates) or infiltration (in warmer climates). DC, being a little of both, has a more challenging sitation, but the problem of air-carried moisture moving through walls must be addressed. If a pipe breaks and no one acts to stop it, and dry the construction immediately (literally), then no well-planned system of vapor retarders, air barriers, positive pressure or any of the other moisture control methods would do a thing. William C. Pegues, FCSI, CCS New member Username: Wpegues Post Number: 10 Registered: 10-2002 Posted on Monday, November 04, 2002 - 11:54 am:    John, Yes, DC is a real challenge here - Very hot and humid during late June through early September - it was originally a swamp! And it can get very cold here, there are always a couple days below 0 F and many days below 32. The stormwater leakage was a real joke. The building was occupied by the condo owners, and it leaked before and after their occupancy. It did not leak into the apartments themselves, but showed up in interesting areas like the health club by creating a water feature with cascading water down tile walls during a couple storms. Of course, it was also doing a lot of 'behind the wall' saturation of materials up the entire vertical face. It went on so long that mold started to grow everywhere. Fortunately, we are not involved in the project in any way. But, there is a lot of nervous fallout into other projects in the aera here caused by this. Suddenly all the Owners are being solicited by 'mold consultants' and experts. There is a way to build the wall on our project that will put the membrane in the right location, insluating the cavity like you suggest. But the Owner does not want to deviate from a standard system of batt insulation in the stud wall construction. We typically do a foil face insulation on the warm side, and a building wrap like Tyvek Commercial Grade over the sheathing. That has historically worked well here in the area, and we have been here a long time and had no problems with it. John Regener, AIA, CCS, CCCA, CSI New member Username: John_regener Post Number: 27 Registered: 04-2002 Posted on Monday, November 04, 2002 - 09:31 pm:    William: Being in DC, can't you just get Congress to legislate the problem into oblivion? William C. Pegues, FCSI, CCS New member Username: Wpegues Post Number: 11 Registered: 10-2002 Posted on Monday, November 04, 2002 - 11:18 pm:    John, Even if I could motivate congress, I am not sure you want them to direct their attention at anything - what you get out of them is anyone's guess -grin! I always thought a good analogy of their logic would be.... "If less is more, then bigger is better" Ron Beard CCS New member Username: Rm_beard_ccs Post Number: 10 Registered: 10-2002 Posted on Thursday, December 26, 2002 - 01:25 pm:    Robin, et al: This is to advise all that an interesting article on “vapor barriers,” or more appropriately termed “vapor retarders” appears in this month’s issue [December 2002] of The Construction Specifier. This article appears to be a very interesting primer on the topic of vapor drive. Maybe someone should pass it on to the “expert” in Boston. Edmund Armstrong, CSI, CDT Unregistered guest Posted on Tuesday, February 18, 2003 - 04:30 pm:    I live in Bucks County, Pennsylvania, which is just on the other side of the Delaware River, in my case, across from Trenton, NJ. Like William, our area has plenty of humidity during the summer, and winters can be quite cold with plenty of below freezing weather and dips into the low teens. In the winter months I keep the indoor humidity very high so as to lower the room temperature but still be in the 'comfort zone.' Accordingly my practice has always been to staple a 4-6 mil plastic vapor retarder on the warm side of the studs, including ceiling members with an attic above. The attic is well ventilated. Periodically I have lifted ceiling insulation to confirm that the vapor retarder is not trapping moisture where it is not desired. I have always been pleased to find no problems - until this winter. During the past autumn months I had been installing some data wiring through the attic and failed to completely place a piece of R-30 insulation back in its original position. Imagine my horror when I was crawling through the attic this winter and noticed droplets of water between the ceiling drywall and the clear vapor retarder where I had failed to properly replace the insulation. The vapor retarder had now become the 'cold side' and was trapping water vapor between it and the drywall. The water droplets made it obvious that the vapor retarder was working nicely but also showed how it can create condensation problems if the space directly behind it is not kept warm. As for a vapor retarder on the cold side - that's a new one on me. Second opinions are in order - or a good dehumidifier. John Regener, AIA, CCS, CCCA, CSI New member Username: John_regener Post Number: 58 Registered: 04-2002 Posted on Wednesday, February 19, 2003 - 04:31 pm:    This vapor retarder in walls thing is so disconcerting ... but indicative of how infrequently we evaluate designs and understand the physics that are going on. I was involved in a hotel project in Florida. The vapor drive worked just like the textbooks say: from warm to cool. That is, from the warm, humid exterior to the cool, air conditioned interior. The wall had a vapor retarder applied to the interior surface, only it wasn't called a vapor retarder. It was called vinyl wallcovering. Worked great as a vapor retarder. Stopped the water vapor. Of course, the water vapor condensed on the backside of the vinyl wallcovering but that was ok. The wallcovering had anti-mildew properties, as did the adhesive. But there was free water that wasn't affected by the mildewcide and it bled through at the wallcovering joints, which turned black from the mold growth. I had a project in California that had a complex vapor retarder situation. You know, California. Land of beaches and deserts ... and high mountains with extremely heavy snowfalls. The design was for a protected membrane roofing system (EPDM with extruded polystyrene insulation on top). However, the insulation worked to allow water (snow melt and thunderstorm rain) to run down between the boards and across the membrane to the roof drains. Hmmm. That means the insulation did not protect the membrane (vapor retarder) from getting chilled by the water run-off. The problem became a non-problem only because the steel decking proved to be an excellent vapor retarder and the residual moisture in the concrete roof deck fill (hard rock concrete because the roof deck had to support a 185 psf snow load) cured and dried thoroughly over the summer months before the roofing was installed. My point is that vapor retarder issues in walls and roofs are not just concerns for architects in cold climates. Lynn Javoroski Member Username: Lynn_javoroski Post Number: 21 Registered: 07-2002 Posted on Wednesday, May 07, 2003 - 04:04 pm:    Re: "Congress" - If "pro" is the opposite of "con", what's the opposite of "progress"? JG (Unregistered Guest) Unregistered guest Posted on Tuesday, June 03, 2003 - 12:26 pm:    Have you had any "known" problems with mold feeding off of concrete block (when a disaster such as a broken pipe occurred and no one fixed it)? (i.e when the walls were concrete block construction). If so, could you be specific in detailing the construction type in full. (We do all interior and exterior walls with concrete block.) John Bunzick, CCS, CCCA Senior Member Username: Bunzick Post Number: 103 Registered: 03-2002 Posted on Tuesday, June 03, 2003 - 12:45 pm:    Mold will not grow on concrete block or masonry because it needs (besides water) organic material to grow. However, in many or most cases, the block is probably dirty after being in use for a number of years. This normal accumulation of atmospheric dust and dirt will provide food for mold to grow. On a building under construction where the dirt has not accumulated, or where the surface of the block is painted and cleaned regularly (such as a commercial kitchen or something), mold growth is unlikely. Russell W. Wood Senior Member Username: woodr5678 Post Number: 6 Registered: 11-2003 Posted on Wednesday, April 28, 2004 - 05:53 pm:    To John Regener or Others For South Florida buildings (humidity highest in US),I've been advised against having vapor barriers in exterior walls period.....exterior walls should allow mositure/humidity to escape to the exterior or to the interior to be removed by A/C. Most Florida exterior wall construction consists of CMU with painted stucco exterior and painted drywall on furring on rigid insulation on CMU interior side. The great debate here in South Florida is always should the rigid insulation on interior side have a foilback (vapor barrier)? Our favorite PHD says no way! Any thoughts? John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 216 Registered: 03-2002 Posted on Thursday, April 29, 2004 - 09:14 am:    I would agree. No way should south Florida buildings have an interior vapor retarder. I'm not an expert in the area of moisture dynamics, but I wonder if the no-vapor-retarder method is the best in south Florida - I would think an exterior one is desirable. There are various software programs (such as WUFI) that can model moisture transport through a wall and help determine the need for a vapor retarder. I have heard of the no-vapor-retarder approach as being a good choice in many areas of the country -- I'm not sure about S. Fla. (WUFI is available at the Oak Ridge National Laboratory web site: (click link): http://www.ornl.gov/sci/btc/apps/moisture/) A larger concern may be that of the benefits of an air barrier. Uncontrolled air infiltration and exfiltration can transport significantly more moisture than migration through building materials. Ronald J. Ray, RA, CCS, CCCA Advanced Member Username: rjray Post Number: 5 Registered: 04-2004 Posted on Thursday, April 29, 2004 - 12:05 pm:    William, my opinion is that in your climate, which you describe as being very similar to that found where I live, the vapro barier belongs on the war side of the insulation (interior.) I would suggest that the foil facing or kraft paper faceing on batt insulation does not provide a continuous vapor barrier. I always specify unfaced batt insulation with a separate vapor barrier, usually 6 mill polyethylene. John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 217 Registered: 03-2002 Posted on Thursday, April 29, 2004 - 03:18 pm:    In Florida, the warm side is not the interior it is the exterior because buildings there are air conditioned, not heated. Russell W. Wood Senior Member Username: woodr5678 Post Number: 7 Registered: 11-2003 Posted on Thursday, April 29, 2004 - 05:31 pm:    That's the whole point in Florida. Vapor barriers can not go on exterior side (warm side) in S. Florida because typical exterior wall construction is stucco on CMU (exterior side). Moisture goes from wetter to dryer, or from exterior to interior. Now, if interior side has insulation with a vapor barrier (foil back) now the moisture is trapped, per our friend Joe PHD, a moisture condum. Just what you want to do trap moisture in the interior side wall assembly-not! However, there are many Architects and Engineers here in Florida that swear we must have the foilbacking on the insulation on the interior side (cool side) of the wall. Ronald J. Ray, RA, CCS, CCCA Senior Member Username: rjray Post Number: 6 Registered: 04-2004 Posted on Friday, April 30, 2004 - 08:44 am:    For recently projects in Houston, Texas, I have specified an air and vapor barrier (WR Grace Perm-A-Barrier Wall Membrane) directly over the exterior wall sheathing on metal stud framing. So far, this appears to be a successful installation. Could this type of membrane, being ”self-healing”, be installed over concrete block with metal lath secured to the concrete block with screws? Anonymous   Posted on Friday, April 30, 2004 - 03:42 pm:    What happens when interior desecrate..I mean designers decides to have vinyl wallcovering (or some other relatively vapor-impermeable "finish") on the interior face of an exterior wall in S. Florida...in addition to whatever vapor barrier/retarder the architect may have designed into the wall assembly? Hmmm..interesting to see what would happen? Gerald S. Deni, AIA,CCS,SCIP (Unregistered Guest) Unregistered guest Posted on Tuesday, May 04, 2004 - 09:31 pm:    I am surprised that there is still this much questioning of vapor barriers. For specifiers and architects requiring data on vapor barriers, air barriers, and mold development in exterior wall systems, I would suggest going into the CSI website. Click on "Construction Specifier". In the "Keyword Search", type in "Vapor Barriers". The Construction Specifier has several very good articles which cover the topics indicated. They detail the problems, failures and solutions. A final note for specifiers and architects working on Florida projects: Never place vinyl wallcoverings on the interior of exterior wall systems. You may be creating vapor barriers on the interior and exterior of the wall, which would entrap moisture within the wall system, resulting in mold growth! Gary M Kehrier, CSI, CDT (Unregistered Guest) Unregistered guest Posted on Wednesday, May 05, 2004 - 12:58 pm:    To All concerned with this issue. I refer you to the AirBarrier Association of America 1600 Boston-Providence Walpole, MA 02081 1.866.956.5888 1.866.956.5819Fax Everything you want to know about who, WHAT, WHEN,WHERE, and WHY may be found here. We are members of this organization (as a manufacturer). I have attended a seminar conducted by the group in Seattle, Wash. and I can assure you that the information is out there and they can be of great service. Russell W. Wood Senior Member Username: woodr5678 Post Number: 8 Registered: 11-2003 Posted on Wednesday, May 05, 2004 - 05:28 pm:    Florida exterior walls do not have air barriers, sheathing, studs, brick, none of it!!! The exterior walls are painted stucco on concrete block (exterior side) painted gypsum board on furring on rigid insulation on concrete block (interior side). Should the rigid insulation have foil backing (a vapor barrier)? John Bunzick, CCS, CCCA Senior Member Username: bunzick Post Number: 219 Registered: 03-2002 Posted on Thursday, May 06, 2004 - 08:46 am:    Here in Massachusetts the industry is moving towards new designs for wall systems. We needed to take into account the code-required air barrier. The most effective solution has been to combine the air barrier and vapor retarder, and move the insulation outside of the ab/vr (using ridid foam) into the wall cavity. This is a big change from batt-stuffed walls with interior poly. It still makes no sense to me that anyone in Florida would put a vapor retarder near the interior of a wall assembly. Maybe Florida needs to find new types of wall assemblies, too. Has anyone run a WUFI-simulation on this? Or requested assistance from Grace Construction Products, who can run moisture simulations? I'd start there. Ronald J. Ray, RA, CCS, CCCA Senior Member Username: rjray Post Number: 9 Registered: 04-2004 Posted on Thursday, May 06, 2004 - 08:58 am:    I am beginning specification work on a project in Eugene Oregon where the designer is proposing the following exterior wall system. Any thoughts related to placement of the vapor barrier or any other aspects of this assembly? Interior gypsum board over 6 mill polyethylene vapor barrier over furring channels, over CMU with unfilled cores. Exterior EIFS system with waterproof adhesive with 3 inches of EPS insulation. Lynn Javoroski Senior Member Username: lynn_javoroski Post Number: 99 Registered: 07-2002 Posted on Thursday, May 06, 2004 - 09:57 am:    Other than the fact that the vapor barrier will be penetrated with every drywall screw, electrical and communication box and picture hanger? What could possibly be wrong with that? Russell W. Wood Senior Member Username: woodr5678 Post Number: 9 Registered: 11-2003 Posted on Thursday, May 06, 2004 - 10:16 am:    My point exactly! Many architects/engineers where I practice (south Florida), feel the rigid insulation must have foil backing (aka vapor barrier)a northern climate practice. However, by the very nature of construction, the foil backing is not a completely sealed barrier. Therefore, the wall is still able to breath and in reality the the foil backing is useless and a waste of money. Anonymous   Posted on Thursday, May 06, 2004 - 01:10 pm:    There are two ways that moisture travels across envelope assemblies - air transport and diffusion. Both need to be addressed. Foil is a vapor diffusion retarder (as are polyethylene and kraft paper). If the vapor duffusion retarder has holes in 10% of its surface area, it is 90% effective. If, however, you have holes in 10% of the air barrier (what you need to control air transport of moisture laden air), serious problems could ensue. Read Lstibureks books for a full explanation. Russell W. Wood Senior Member Username: woodr5678 Post Number: 10 Registered: 11-2003 Posted on Thursday, May 06, 2004 - 03:04 pm:    Joe Lstiburek PhD advises not to use vapor barriers in exterior walls in Flordia. That I know. However, some of my south Florida colleagues disagree with Joe. I believe they disagree because they're transplanted northerners applying northern logic. Hence, I seek a third (or forth) opinion. Anonymous   Posted on Thursday, May 06, 2004 - 08:02 pm:    http://www.buildingscience.com/resources/walls/insulation_sheathings.pdf Anonymous   Posted on Friday, May 07, 2004 - 10:57 am:    Not that I have any association with this, but Mr. Lstiburek is doing a seminar in the Twin Cities that will touch on this subject: http://www.cala.umn.edu/cps/spring2004/6570.html And, good information to know at the Building Science post. Anonymous   Posted on Friday, May 07, 2004 - 11:37 am:    He will also be speaking at the CSI Puget Sound Chapter in Seattle, WA on May 13. Anne Whitacre, CCS CSI Senior Member Username: awhitacre Post Number: 89 Registered: 07-2002 Posted on Monday, May 10, 2004 - 12:04 pm:    ... regarding the wall assembly in Eugene -- and the fact that most insurance companies are not covering EIFS assemblies, there are municipalities that won't allow it in their jurisdiction, and it fails more often than nearly any other exterior wall system, its clearly the recommended system for the Eugene Oregon climate where even GOOD exterior wall systems often leak. Are you sure this guy is a "consultant"?