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I’m building a new home here in southern Ohio. All the research I’ve done says to install a continuous poly vapor barrier walls and ceilings. I’ve gotten bids from 2 insulation contractors so far. Both are advising installing poly on the walls only. Both have warned me about the same thing– on the ceilings, moisture migrating through the drywall can become trapped between the poly and the back of the drywall where it can cause the popped ceilings or paint to fail. One contractor even said if I insist on poly on the ceiling I’ll have to sign a release of liability. Have you insulation experts encountered any such problems with poly vapor barriers on ceilings?
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Replies
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no , sounds like b*s*..
if the attic is properly insulated with no cold spots.. how is the vapor barrier going to drop below the dew point ?
if that surface is not below the dew point it cannot become a condensing surface so the moisture will stay in the air and will not collect on the back of the sheetrock...
if there is a cold spot... the drywall itself will be below the dew point and the drywal will become a condensing surface...
why in the world does an insulating sub care if they're installing over a vapor barrier ..
did you ask them why all of the fiberglas insulation mfrs sell their product with a vapor barrier attached..?
am i mssing something here ?
*Mark. Mike gives good advice and raises important questions.I would not worry about moisture migrating--diffusing--through the gypsum wall board (GWB). My main worry would be the moist warm air leaking into the attic from the many penetrations of the ceiling below the attic..attic floor. For example. With a 10 foot by 10 foot sheet of GWB, it would take one year for one cup of moisture to diffuse(migrate) through it. But if you had a 1-inch hole in that GWB, 20 gallons of water would move through it in one year. With a couple of coats of latex paint on the ceiling GWB you need not worry about moisture geting through.As noted, even if some mositure got through the GWB it would be a small maount that would take a long time to get through. If you feel more comfortable with a vapor diffusion retarder(VDR) install it. While you are at it go into the basement and seal all the openings in the basement ceiling. Do the same thing in the attic floor before it is insulated. These openings in the basement ceiling allow the basement's warm moist air to be sucked up into the attic space. Sealing these holes reduces the need for attic ventilation and lessens the chances of ice dams forming. Use plenty of blown-in cellulose insulation in the attic. Hope this helps. GeneL.
*Hi Mark, your insulation subs are wingnuts, find other subs.Gabe
*In our area, poly is not used on ceilings....only the exterior walls...Drywall problems with staining at the nails and other problems....Ceilings are ussually spec'ed with kraft faced fiberglass....near the stream thinking your subs may have had some past troubles as has happened around here,aj
*Hey AJ, were these ceilings insulated with batts or blown-in or cels. If batts, were they edge stapled or face stapled? It seems that something is terribly wrong if the sheet of poly just behind the drywall is the first condensing surface. Now if it covered with inadequate insualtion, that's a different story. Were these houses wet?I have ceilingsand walls blanketed with taped foil faced foam sheets under the drywall.No stains or hints after 6 years.Our humidity in winter is high enough that we will get slight condensation at the edge spacers, will quantify this season.-Rob
*Rob....problem ceilings were with unfaced fiberglass batts and poly...Standard around here is kraft stapled inside the joists...if you staple to the face edge of joists, the drywallers will either not do the job or basically get even with you somehow for making the boards a real pain to hang.near the stream,aj
*AJ you live in a very strange world. I can't believe you're a carpenter, much less a builder or contractor. You can't believe that crap that you're writing.Only a shmuck would do half a job and then spread false stories to support it.Gabe
*Gabe,So it would seem, but I have been told by more than one local carpenter here in Central New York that you shouldn't put a vapor barrier in the ceiling because "it needs to breath". I know you and I have had our differences about the wisdom of poly as a vapor barrier, but I think we both agree that a sealed ceiling is better than a "breathing" ceiling.My point is that AJ probably is really a carpenter doing just what he says he does, because I've run into a bunch of 'em down here who do the same. Local folk wisdom is a powerful force. Not that it's correct.Steve
*Steve, you're probably right. Seems that I still run into the odd carpenter who asks where to put the small step, at the top or at the bottom of the stairs. Seems that they can't calculate the proper rise for a set of stairs, so they use a standard size for all the steps and adjust on the last one. Like you said, just because more than one does it, doesn't make it right......Gabe
*Gabe,You mean there's a way to make all the steps the same size? =:-OThat's hysterical! Where to put the small step. Gotta remember that one to tell at work tomorrow.Steve
*Gabe, I'm not defending the practice, but what AJ describes is SOP in northwestern New Jersey, as well. At least it was when I left the trades four years ago. Nothing annoyed the drywallers more than batts stapled to the face of the studs. To the best of my knowledge, I worked in one house that had poly in the walls or the ceiling, and I never built one of my own that way. We just didn't know any different, because that's how the guys who taught us did it. No building inspector in my experience so much as whimpered at the practice. Andy
*Steve and Andy....Thanks for the posts in support....Gabe...sorry you need to debase me...To further clarify....I described what is standard around my area...b I didn't say I did it did I.....I have enjoyed all the ideas that all post here, even the Canadian super sealed R2000 ideas...The more interest the better I say...Near the stream,aj
*AJ do you know what happens if you run your prop backwards?High above you,Gabe
*I am baffled by the practice of stapling the flanges on the inside. I have hung rock over face stapled batts and didn't find it the least bit challenging.Maybe it is simply the "I have been doing this for X number of decades and bitch at anything that is different or challenging." type attitude. Or maybe it's plain arrogance.The upside of face stapling is that the insulation will actually work. Imagine that.The people that push this practice need to see the presentation that advanced energy has on this stuff and how the insulation is nearly completely negated by this practice. They have pictures, IR photos and video of sveral houses from framing to occupation that vividly show the effects of this practice negating the insulation.What if the insulation manufacturers made the flaps blaze orange. Would the rockesr see them OK then? How bout if they glowed in the dark??-Rob
*Rob...Go to a development or two and yak with the drywall hangers...They are the ones that want it stapled on the inside...The manufacturers also OK it...(Read a package) The books explain and the rockers will tell you that it's no fun pushing the rock tight to the studs with the insulation puffing...It has nothing to do with finding the studs....When the boards are not tight, the fasteners will tend to punch thru the paper often and there will be way more nail pops down the road also...The taper ends up banging more nails in and on and on...It just works way easier for them the other way....I'm not condoning it, just explaining it...near the stream,aj
*How do I insulate underneath a post and beam house on blocks? Insulating between joists on old house that's up on blocks. Central Texas. House is two feet off the ground. Joists are 2x10 rough cut cypress, set at approximately 24" intervals. Do I need a moisture barrier between the top of the insulation and the bottom of the floor? If so, is Kraft facing enough? Or should I staple up a plastic lining before installing the insulation? Wire screening to hold the insulation up?
*barbarn...what's your heating sytem ? and what is the crawl space like....dry.. sandy ? vapor barrier ?whatcha got ?
*Gabe, where you live? I'm in Arkansas and have looked at 100's of new homes over the past 15 years and have NEVER seen a poly vapor barrier used. And most of the insulation is stapled to the sides. That seems to be the way it's done. You come down here and do it otherwise, and you'll be a "nut." Building practices are regional.
*Eastern Ontario, Canada.Yes Crusty, most building practices are regional. Doesn't make it right and doesn't make it wrong, only makes it regional.Here we tend to take energy loss rather seriously and have developed a very efficient house envelope. Doesn't mean that it would work as well in Arkansas.But that's the benefits of this forum, the exchange of regional information for others to compare and learn from.Gabe
*I have really struggled getting people to do anything "different" on my house. I try not to tell them how to do their job, as you've all warned me so many times, but it takes lots of "encouragement" to get them to try something different. We compromise a lot, a lot more than if I lived in Ontario Canada!
*b WBA At Your ServiceHere in the Lehigh Valley, only DIY's staple over the face. The drywallers demand side stapling so they can glue directly to woodto help prevent nail-pop callbacks.
*As Crusty says, I'm having a difficult time pursuading the subs to consider doing things a little different. Here in S.W. Ohio the norm for insulation installs is to stuff walls with unfaced FG and cover with poly; on the ceilings, hang the drywall and blow in FG or cellulose-- no vapor barrier at all. Or side staple batts. When I suggested I want poly between the drywall and blown in in the ceiling they think I'm nuts and start talking about how I'll have moisture on the ceilings.
*crusty... tim.. mark.. what can i tell you.. i fought all those battles in the '70's and early '80's.... now we've got enough diversity and high heating bills so we can find the subs who do it the way it should be done....they're out there where you guys are too.. you just haven't met them yet..and i can sure sympathize with the difficulty of dragging them along...some things are definitely regional... but some things are wrong.. just another example of a failed energy policy for the last twenty years....if it ain't code...it don't happen.....if those subs were in massachusetts.. they'd have all their work rejected.. all plans have to comply with mass-chek... an energy code compliance software... as far as i no.. it's the model code for the national one that we'll all be facing.....if you ever get the chance.. go to some of those seminars that the DOE sponsors....on ((Energy Star)) homes...lots of good info... lots of give-aways like lstiburek's books for different building in different climates....as a matter of fact.. if you can get your homes into the energy star program.. you get lots of good things.. about $3000 worth.. including spray foam... blower door testing... HVAC design and testing...check it out...
*Gentlemen. Yhe common, widespread but incorrect practice of inset stapling of fiberglass batt's Kraft paper flaps is wrog. This practice both compresses the insulation and creates air channels both of which reduces the insulations effectiveness.When fiberglass (FG) batts are compressed both the density and the R-value increases, but the overall R-value decreases. Even though the R-value per inch increases as the batt is compressed, this does notcompensate for the loss in thickness. The result is the lowering of the overall R-value. For example:A full 6-1/2 inch R-19 batt has an R-value per inch of R-3.04. When ompressed in a 5-1/2 inch 2x6 cavity the R-value per inch rises to R-3.27, but the over all R-value drops to R-18: R-3.27 x 5.5 inches equals R-18.All combustible building materials give off smoke and flame speading when burning. The codes determine how much smoke and flame spread is permitted for a particular material.The 1993 BOCA code, Section 723.3 Concealed installations, requires that insulating materials in any type of building contruction must have a flame spread rating of 75 or less and a smoke-developed rating of 450 or less. However, Section 723.3.1 Facings, say that when insulationmaterials are installed in concealed spaces (such as walls...) flame spread and smoke-developed rating limitations do not apply to facings,provided that the facing is installed behind AN IN SUBASTANTIALCONTACT WITH THE UNEXPOSED SURFACE OF THE CEILING, FLOOR OR WALL FINISH. The flame spread rating of uncovered Kraft paper is in the thousands.The fact that the tapers do not seal the bottom of the gypsum wallboard to the floor, combined with the airspace caused by the ompression of the batts spells trouble. Gene Leger D
*The latest insulation contractor is telling me that a poly vapor barrier is OK for the heating months but during our couple of months of hot humid weather warm moist air from the attic will migrate through the 12" of fiberglass insulation and will condense on a poly vapor barrier and "puddle". He's telling me we need to leave out the poly so any moisture can permeate through the drywall and disipate. Anyone experienced this problem?
*what's the sense of answering that one... they'll only come up with another fable and then that will have to be refuted....the warm moist air is comming from_____________. (fill in the blank)if the answer is from outside... then you need to vent. your attic.. soffit vents and ridge vent..if you have no vents.. then the only source will be your house... so control the moisture source...
*Mike. If Mark lived in the south you would tell him Not to instsall a vapor barrier anywhere on the interior. But what do you tell those living in mixed temperate climes (MC}? In TC a vapor barrier (VB)would be in the wrong place for half the year. The question then becomes (a) do we need a VB?, (b) when do we need a VB? (c)where in the wall is it needed?, or (d) replace the VB with a vapor diffusion retarder (VDR) and create a flow-through design. GeneL.
*southern Ohio.... which is north of me....vapor barrier and vented attic...or some other solution.. the guys that are talking to mark don't have solutions.. just excuses.. and the wrong ones at that.....so your arguement is not addressed to me genel.. tell it to mark..... i think you and i pretty much understand each other....the important thing is to have a strategy and a plan to implement it....
*I'm thinking these guys can't be right either--- why else would it be OK to put up kraft faced batts but not a continuous unbroken vapor barrier. Condensate would form just as easy on the back of the kraft.
*Mark. Becauuse you don't want a vapor barrier all the time which is what the polyethylene is. You want a full time air barrier, and a vapor barrier in the winter time, but a vapor diffusion retarder in the summertime which is what the Kraft paper is. GeneL.
*Mark: I went through the same head scratching on my new home. After I came in and saw that the poly only went to the top plate, I started asking some friends in the trades and pretty much got the standard "that's how it's always done". I think it is a very regional thing, and right or wrong, MY particualr climate (central cal. mtns.) seems very forgiving with regards to moisture problems. We get so little precip. and humidity that we seem to get by just fine with marginal venting, flashing, etc. Is it right? not likely. Would I do it that way again? not likely. But as a firefighter by trade, who works in an area where building is booming, I get to walk through a lot of houses under construction, and this seems to be the norm around here.So here I sit with unfaced batts, poly on the walls, blown in cellulose in the attic, and a furrow on my brow, looking at heating bills that are a fraction of what they were in the old place..........wedge
*Mike,Just noticed this post. Southern Ohio is south of you. Even N Ohio is at best even with you. I think Gene hit the nail on the head about mixed climates. Even in my part of Ohio, poly on the ceiling isn't SOP.I know of one case where the ceiling had to be removed and the poly torn out because of condensation under the insulation. The house had ridge vent.Looks like in this case as many others, local rules rule.John
*I live and build in the Northern part of Michigan in the Harbor Springs area and with the cooler temperatures I always use a 4 mill poly vapor barrier in the ceilings. I have literally walked on frozen blown in insulation in attics around bath areas. (no VB) I have seen frost on the outside wall cavities while opening walls with blown ins. and where vapor barriers were not intact. But then again we heat our homes about 9 months out of the year. I'm more concerned about my heating bill rather than cooling.
*Dale,What kinds of blown insulation have you observed this in?Steve
*Yes, what kind of blown in insulation has been frozen enough to walk on ... for that matter, frozen at all ... walk on or not.
*This is a pretty confusing discussion. Certainteed states that for residential construction vapor barriers are not a standard recommendation for attics.For those who feel that a vapor barrier is required below an unheated attic ceiling isn't it really dependent on region?
*You venturing into controversial and love-hate relationships with this thread. Some people have left this forum permanently as a result of the animosity engendered by this discussion. So many factors have to be considered, we could not establish agreement of the rules without kowing the specific design, construction method and materials in the house and specific climate factors.I would not want to use fiberglass in a ceiling that has no VB underneath since any moisture that gets to the FG will migrate down to the drywall. On the other hand, putting a ceiling VB in a poorly weatherized and improperly vented house will undoubtedly lead to wet and stained ceiling drywall.
*Northern climates....Kraft faced insulation is not staining ceilings. That is all I am sure of...near the stream,ajI still think that some homes have very excessive moisture. My own home does not, so I think a home like mine could handle many insulation methods.
*Regarding venting: I'm currently re insulating a cape style dormered cathedral roof. After removing all the sheet rock from the smallest room I discovered squrel damage and the remnants of what was once insulation. (squire problem solved) I have packed insulation into the duct area that contains a 2"x4" pocket of air space adjacent to the gutter. I then sprayed foam insulation capping the pocket and sealing the air space between the roof and top of the first floor exterior wall. This gave me a tight seal between the R-25 Encapsulated insulation, installed into the roof rafters, and the smooth edge of the spray foam. I then plan to seal the interior with 6mm ploy. My question is air flow. I've concluded that this dormer represents living space and therefore must not be vented. I'm I on the right track? (I sealed the vent near the ridge and insulated the rafters completely up to the ridge)
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I'm building a new home here in southern Ohio. All the research I've done says to install a continuous poly vapor barrier walls and ceilings. I've gotten bids from 2 insulation contractors so far. Both are advising installing poly on the walls only. Both have warned me about the same thing-- on the ceilings, moisture migrating through the drywall can become trapped between the poly and the back of the drywall where it can cause the popped ceilings or paint to fail. One contractor even said if I insist on poly on the ceiling I'll have to sign a release of liability. Have you insulation experts encountered any such problems with poly vapor barriers on ceilings?