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I have just finished insulating a dormer.I used a kraft faced insulation,going over that with a poly.Is this wrong?My inspector told me to rip it down. l
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your inspector is a dufus...
the kraft vapor barrier is just fine IF it isn't ripped... IF it is continuous....
IF it is stapled to the face of the studs and then tape applied over the joints..
but other than that... it is NOT a vapor barrier.... too many holes ... too many edges... too many gaps..
*Mike, are you sure you read Hughs comment correctly?, he installed poly over the kraft batts and the inspector told him to rip down the poly. I agree the inspector is a dufus.........
*Kraft is never installed correctly anyway...but still, I don't even really consider kraft to be a vapor barrier.If he's concerned with you having a double barrier, I'd prefer the poly over the kraft. Choices? Does he want you to remove the poly and leave the kraft? Or literally rip everything down?Too bad you can't slip your arm between the poly and the kraft and slice the kraft vertically with a utility knife. Or can you, since it's a dormer?Next time go with unfaced friction-fit batts w poly. Or, be da real man and go cells.
*The inspector is doing his job...poly or kraft is what they want...Standards and inspectors aren't perfect...but we the people want both...Mike...youse love rules...you love zoning...if yaa love rules then don't undermine an inspector who is enforcing your loved rules.near the stream,aj
*aj.... show me the rule that says you can't have 2 vapor barriers..one that works (poly) and one that is a waste of time (kraft)...the inspector has substituted his judgement and lack of knowledge for the energy rules...but he's the inspector.. so make him a deal...when we had a dufus.. i used to give him 3 for 5...he'd name 5 things and i'd fix 3..... that was the usual ratio of real rules to the ones he was making up...
*Well...we differ Mike...It is my rule to not have two...near the stream,ajIt is also my rule to be friends with inspectors.
*I'm usually with ya AJ, but I gotta say I agree with Mike on This one. Though really I'm starting to think all vapor barriers are a mistake, and therefore, forced to choose, would go with the kraft and ditch the poly, simpy because the kraft would do less damage (ie: i woudn't function very well as a vapor barrier).Steve
*aj.... yes grasshopper... that also is best rule..""It is also my rule to be friends with inspectors. ""
*You can use both Poly & Kraft back as a vapor barrier together. Check out the attached article form Certainteed, note pg. 2 (#5 Installation).
*Geez, if you're putting them against each other, with no appreciable air gap between them, there's no reason you couldn't use 5 or 6 vapor barriers. What you don't want is a barrier on the outside, and another on the inside. The cold side barrier is going to cause condensation.If an inspector doesn't understand simple physical principles, what the heck business does he have being an inspector?
*If you are using two vapor barriers right next to each other its important that your best vapor barrier of the two, is the closet to the moisture source.
*I'm putting up 8" beveled cedar siding over osb sheathing on a small addition. A buddy recommended putting roofing felt over the osb before I put up the siding. The rest of the house has the siding directly over the sheathing. Do I really need the felt as a vapor barrier or is it more important to let it breathe? Any suggestions?
*glux... for a lot of reasons .. the 15# felt is a great idea behind your cedar siding.. and it will FACILITATE "breathing", besides forming an effective rain screen..also backprime and edgeprime your siding before/during installation...and there should only be one nail in each course .. so the nail goes just above the tip of the undercourse...ie..if your headlap is 2" the nail goes about 2.25" above the butt....if your lap is 1.5" the nail goes about 1/75 " above the butt..
*YOU GUYS NEVER ASKED HUGH WHERE HE LIVES!!!!!!Don't you think it would be good to know this when discussing vapor barriers?If you think the location of the house is not important in discussing vapor barriers then do us all a favor and STOP DISCUSSING VAPOR BARRIERS!!!!So Hugh, where do you live?-RobP.S. - Steve and Mike loose 5 points for their replies!
*rob.. y r u shouting ?
*Rob,Oops. And I was just getting caught up on all the points I lost in my last dust-up with Gabe ;-)Steve
*Well Rob is right, if a bit loud. So does Hugh live in an area with more than 2200 heating degree days or with an average January mean temp. of less than 40 degrees?Jeff
*I was shouting because we ought not be throwing around vapor barriers willy-nilly.The potential for damage even in a "code-approved" installation is high, so let's not make it worse.I also believe vapor barriers will soon be seen as the Osama Bin Laden of the mold wars. He didn't really fly the planes, he just caused it to happen.-Rob
*Rob,Please explain your statement about vapor barriers causing mold to happen. I am not a builder, I design HVAC systems for a living. I am probably asking you to repeat something you have said before, but humor me if you will.
*Yes, Rob, please do. Are you asserting that a warm-side vapor diffusion retarder contributes to mold growth? Where? Most of the serious problems that have occured have been inside wall and ceiling cavities where a vapor retarder would reduce the intrusion of moisture-laden air into the construction thermal envelope.Please elaborate -Jeff
*What about poly vapor barriers between basement walls and firring? Any associated problems?
*dean.. it's hard for me to put fiberglass and super insulated in the same sentence...substitute cellulose wherever you said fiberglass and it sounds like a pretty good system..denspak with no vent wouldn't worry me..but i use vents .. soffit and ridge.. and my ridge vents are Shingle Vent II
*I don't know Rob's take on this Jeff, but I can imagine several situations where this can happen. Brick veneer wall on the west side of a house. Housewrap on the sheathing, poly inside, air conditioned interior. Summer thunderstorm soaks the wall, sun comes back out. Moisture drive is warm to cold. Wet brick heats up, water in vapor form exits the back of the brick (or liquid water in the cavity between housewrap and brick vaporizes). Housewrap does its job and passes moisture vapor into wall assembly. The first condensing surface that the vapor is likely to encounter is the back of the poly. It condenses. Now, there's not enough heat in the wall for some time to change the phase of that water again, so it can't migrate back out as vapor either way. Mold grows. You could subsitute almost any type of siding for the brick. I think it's important to build walls that have the potential to dry if they do get wet. Poly on the inside compromises that potential. And since most moisture gets into framing cavities carried by air currents and not vapor diffusion, I think air sealing should be the prime defense, rather than vapor barriers. Of course, if you live in Manitoba, maybe a VB is a good idea, too. But I've talked to a number of building scientists who say that if you plan to air condition the house at all, you should not use a poly VB.Andy
*Andy,FHB has done articles on air tight drywall and the use of vapor barriers, wall and roof venting, etc. Each article has real world merit that has/does work, yet there seems to be no consistant message. The articles are well written and supported by Building science sources in all cases. The science of building construction and material is constantly evolving. It is difficult to keep up with, and in many instances totally confussing. Different areas of the country require different approaches to similar, but not quite the same problems.Could FHB address some of the evolving issues, such as indoor air quality, mold formation, vapor tranmission, and anything else that comes to mind related to energy efficient construction? Nothing seems as simple as it was 20 or 30 years ago when energy was cheap and construction materials had not evolved to the hi-tech level that they are heading for today. We as builders and remodelers are often caught behind the curve in this whole process. What was considered right even 5 years ago is now being considered the source of a new problem.Anymore I am hesitant to embrace anything that hasn't proven itself for at least ten years, no matter who indorses it. Now that mold has become the nemisis of building a tight home, what are we to do? Untill vabor barriers are proven to be the causitive factor in the equation, I don't think I will stop using them.Dave
*Dave, the whole onion is too big a topic for even an 8 page article, which is the biggest we do. Building science is fascinating, though, and I intend to continue to pursue articles on it. That said, we have covered many of the topics you suggest. E-mail me at work, and I'll send you a list of articles and issues.One other problem is that much of the research I've seen suggests that several code-mandated methods really can do more harm than good. Among these are such entrenched ideas as vented crawlspaces, poly vapor barriers and vented attics. That problem raises the question: How much space should we give in the magazine to good construction practices that won't get by a lot of building inspectors? I think discussing these topics is valuable, because codes don't change without pressure. But that's a long term proposition, and not as useful as information on techniques that builders can put to use today.FWIW, my building inspector bought into the argument against vapor barriers. I don't have one in my house.Andy
*Andy - the CW on housewraps is "Don't use them with brick veneer - use felt paper." I totally agree with you that it's important to build walls that have the potential to dry if they do get wet - I think that is one of the most important issues in construction today. I also agree that A/C (and A/C overuse/overcooling) is one of the 'smoking guns' of residential building science - by chilling a house to 68 on a 95 degree day you are almost making it like a refrigerated building, hence reversing the proper side for vapor diffusion retarders. On the other hand, I have some reservations about no-vapor retarder-warm side, housewrap-cool side wall construction. The breakdown of housewrap under aggressive surfactant, agressive tannin action (proven here - we've just heard of a 10 YO, local, unprimed cedar siding disaster w/Tyvek) leads one to wonder what effect milder surfactant action, from sheathing and other sidings, will have over time. They don't break down felt paper. If you have liquid water (condensate) within a wall cavity, housewrap will do one of its jobs (waterproofing) and hold it in - so obviously if we are going to use housewrap we cannot allow dew point to occur within wall construction.I think that Paul Fisette (U Mass?) is one of the leading experimenters in this field today. I hope that one of these days we could get some definitive answers ... I'm tired of arguing the housewrap-VDR scenario. Maybe FHB/Breaktime could take the lead on standardizing some of this information? (Once we agree on what it should be!). See Dave Richeson's post below, with which I agree.Jeff
*Thanks for the reply Andy. I have every issue of FHB since late 1984. Maybe having read so much on energy efficient homes is what is confussing. I am not pointing the finger at FHB for publishing contraditive articles, but that is a problem with the evolution of building science. The "flavor of the month" has its run untill someone has a problem or it is proven to be a problem. In some ways I am glad that the code enforcement agencies are slower to change than we "builders ". The house wrap issue is a case in point. It is now approved in my area, and to the concensouse at FHB and the Breaktimers is it is not as good as felt paper. Now I am waiting for a recall because I have used the stuff for ten years or better. Did I do more harm than good? I hope not. If I gave my customer an inferior product through good intentions and code compliance, then I am still wrong.As you have said, it is a pretty big onion. FHB is doing a great job at keeping us informed. That is why I continue subscribing year after year. Maybe I need to get into some type of continueing education course just to keep up.Thanks agian,Dave
*Andy,Your brief description of a the brick veneer scenario is as concise an argument as I've read to date for omitting the poly in under certain curcumstances.Maybe I'm not crazy after all for thinking that poly is not always a good practice. Though certian posters around here will box me about the ears for saying so ;-)You are lucky to have an inspector who is open to discussion.Steve
*Yes fortune smiles on those having an inspector who will actually listen to reason or anything else for that matter. The job of inspector is like being a cop, who has to work in a system that is not quite perfect, but with which without, sleaze ball contractors and their lack of integrity would run amuck! In our part of the world, Canada, there is a need for some sort of inspection on insulation & Vapour Barrier but the existing code rules and their applications seem off balance. They mix some good ideas with some real trash and disregard many blatant errors while strictly enforcing a few rules. As the great saving, miraculous, new materials and procedures engulf us we still need to think, be informed, work within the system and change the sucker all at the same time. Sadly, being responsalbe, in some circles, is not as important as slapping up shacks and cashing in. Outside of a good frame job (structure) the whole idea of a building as a system or living breathing entity is important, sometimes beyond what is normally thought of. Heat, air, and moisture are components that act on and interact with your house entity. They are influenced by the building envelope, the occupants (all biological forms), and the mechanical systems. So... what ? We all need to learn more, ie. become more educated, educate others including all trades & home owners and work at improving standards regionally specific without so much #*!!#^ red tape that it chokes us making solid construction over-designed and over priced. Ask questions.
*I'm convinced that there is so much contradiction in building science because each house is different, each climate different. Lab conditions don't exist in the field. Yet for the most part, codes and products are developed in labs and are intended for broad regional use. I am continually amazed to see builders who use no felt or housewrap, make no attempt at air sealing floor penetrations and who think that caulk is flashing. I once was talking to a builder who said that he wouldn't use blown cellulose because it can settle. Right behind him was a poly-mesh covered wall filled with blown fiberglass. The FG had settled an inch or so from the top plate. You know, I just wanted to run out of there screaming. BTW, while I don't have a VB, I do have dense-pack cellulose in my walls. There isn't much air getting into those walls to transport moisture to the back of the sheathing. I also have DP cellulose in the attic. After the joists were down, I sheathed the attic floor with 1/2-in. OSB. The rafters rest on a plate atop the floor, and are hurricane-tied down. Andy
*It is important to understand building science principles but it is also just as important to recognize the nature of building construction. Buildings and the construction process do not exist in an ideal world, and it is the compromised - or "likely to be compromised" reality of construction that we must take as our departure point. Let's face it. Construction is never "perfect" so our solutions and our applied building science must take that into account. From this I would suggest the following fundamentals:-Insulated building assemblies such as walls and roofs should be designed to be moisture tolerant. By this I mean they should be built with materials that will not be damaged by minor periods of wetting. Futhermore, they should be capable of removing moisture at a rate that eliminates the potential for damage.-Insulated assemblies should be designed to dry (they should not be designed to "breathe" whatever that means...). Maximum drying potential should be the goal and in many climates this will mean allowing for drying to both the interior and the exterior.-Wall assemblies should be designed to be airtight but vapor permeable. Air leakage tranports much higher quanitities of moisture into insulated assemblies than does vapor diffusion. This transport mechanism should be eliminated to the extent possible. Vapor diffusion is the mechanism by which most walls dry, so it would be foolish to build the wall assembly vapor tight. Polyethylene creates a vapor tight wall assembly and of course when it is installed poorly as it usually is, there are numerous air leaks, allowing large quantities of moisture to enter the assembly. Roof assemblies can utilize either vapor diffusion or air movement (venting) to remove moisture. Venting should be considered a backup control strategy however. The primary strategy should be air sealing to minimize wetting potential as much as possible.Last thoughts: All insulated assemblies should be designed with redundancy (i.e. multiple lines of defense). A wall, for instance, should have a primary barrier (cladding, trim, sealants), a secondary barrier (building paper & flashings), as well as allowing drying and being built from moisture tolerant materials. Now depending on your location (site specific exposure), exterior climate, and interior climate (i.e. temperature and humidity levels), there will be many different approaches that recognize the principles listed above.mike chi
*What I am getting from this conversation is if you can build a air tight wall then putting up an interior vapor barrier is correct. If you dont build a air tight wall using a interior vapor barrier or exterior vapor barrier is incorrect.
*I would say that if you build an air-tight wall, then in most cases south of Yellowknife, a vapor barrier is irrelevent.Andy
*You might even argue that it's harmful in an airtight wall, as the VDR's primary function will become to retard the ability of the wall to dry to the inside when conditions would otherwise promote it.Steve
*My thinking on the previous post was that using todays standard framing methods it is almost impossible to build a air tight wall. So what is the purpose of an interior vapor barrier? To keep interior moisture from migrating into the wall or to keep exterior moisture inside the wall or just simply to cut down on air drafts?
*I have live in Arkansas all my life, most of it in the more humid eastern part. I've always been fascinated by houses under construction, and have looked at many, many of them. I have NEVER seen a poly vapor barrier used on the inside. Most houses built in the last 30 years here are brick or vinyl (or a combination). Very few with wood siding. And I have never heard of a mildew problem in a house, other than from a crawlspace that stays wet for some reason.But, a few years ago one of the local electric cooperatives started making builders use poly vapor barriers. It was an absolute disaster! Most of the houses had to have the drywall on the exterior walls completely removed and replaced.So location matters. My opinion is, that at least some of what passes for "building science" is simply a solution in search of a problem. Much of what has been done in the past is fine, no improvement needed.
*Andy,I have only been a subscriber of FHB for about 2 years. As I said when I touched this off by asking Rob to expand on the vapor barrier issue, my interest and profession is HVAC. As indoor air quality plays a part in this issue, and as one poster mentioned overcooling/air conditioning, my question is: has FHB ever done any article on good HVAC design for air quality and moisture control in houses? My experience is that residential HVAC is left up to the contractor with little thought beyond first cost and the heating scheme. I've seen articles on good wiring practice, a bad idea by Susan S? on locating the thermostat where it looks good, never one on good HVAC or ventilation (inside the house, plenty on soffits and the like). Maybe this is better the subject of a new thread.Tim
*Tim, I can't think of us ever having done such an article. I can imagine its value, though. You should e-mail me so that we can bounce some ideas around.Andy
*Tim, excellent idea! It has been my experience, like yours, that there is no "design element" in residential construction HVAC.Andy, please do run with this one. It all ties together under the HVAC umbrella. To me, energy efficient building is not just about tight building, but also indoor air guality (which includes humidity levels), and proper system design. Each space in a home has its own specific supply and venting requirements, yet they must all work together. A delima for most mechanical contrators that don't have engineering support.Dave
*Just a little personal experience on the vapor barrier issue. Over the weekend I was demolishing some of my 1970 house. Wall construction is cedar siding over armstong, 2x4 studs on 16" o.c. with r-11 fiberglass batts and a poly vapor barrier over the insulation to the inside of the living space. House located in heavy woods in northern IL and for most of its life, had no forced air, electric baseboard heat a few TWACs for ac. Very poor ventilation. High humidity due to heavy shade and general area. I have recently removed all the electric baseboard and window units and installed a forced air gas heat/ac system. Past damage is done.What I found in the wall is directly adjacent to the vapor barrier in the fiberglass: black mold. Signs of condensation of the studs and bottom plate, though no serious damage there.
*A couple of other thoughts:Most S-GRN lumber that we see around here already has black mold on it. No one will frame with anything else (here). Could the issue be that mold spores are introduced by lumber into wall cavities where they find a suitable environment in which to flourish, even though the wall cavity may not be 'wet'??Could we persuade the fiberglass insulation folks to add either (a) dessicant or (b) mildewcide/mold killer to their product?For instance, a natural presence of copper or zinc in solution (such as copper or zinc flashing/ridge roll) will kill off most anything on a roof. Why not incorporate such an aspect (copper ion content) into insulating products?Do we need to sanitize lumber, somehow? Mild CCA treatment?OK - here's another thought. Frame, sheath and then spray everything with a combination wood sealer/fungicide before insulating. Might add some cost but how much? $750? Might be worth it.Jeff
*Jeff, the cellulose makers already do that. The borates added to cellulose are fire retardants as well as preservatives. Also, I'm told that there are areas in the south where it's common to spray the frame with a borate solution before moving on with construction.To my knowledge, mold spores exist almost everywhere. They will be dormant unless the proper conditions exist; high humidity and a good temperature. Andy
*Andy - right on cellulose - maybe the FG industry needs to find a way, too. I hadn't heard about spraying framing in the south - maybe that's an idea that should become more prevalent.Thanks,Jeff
*Andy, mold is literally EVERYWHERE!!-Rob
*Rob - You have a good point. The question is why we are seeing so much "problem mold" today. For instance, our 1932 balloon frame is largely uninsulated (still). It also, historically, has had a history of wet basement areas, although we have taken steps to reduce that somewhat.In a couple of cases, I have had occasion to open up stud bays for one reason or another. The metal lath used in the 30's had a paper backing, sort of a brown kraft. If you look at it, you can see some spots of black dusty mold on it even though we have no vapor barrier, no insulation, etc. We have had no problems from that to date. I would agree that a certain amount of mold is inevitable, but what are we doing today to encourage/discourage mold growth?Another example is our municipal building (under construction). The low-bid contractor's bond was called due to non-performance and the building sat, partially-completed, for months. During that time, the mechanical systems were non-operational and interior conditions developed that allowed for significant mold growth. It cost the taxpayers over $300,000 to remove it.I think there is more we need to do to understand this issue in buildings.Jeff
*Fungi grow only in an environment that is 60% rh or greater. Bacteria and viruses will flourish at both above 70 and 60% respectively and below 30 and 50% respectively. The taxpayers money could have been saved by a competent engineer that understood IAQ. Once the mechanicals were functional, start them up and let them run. The mold would have disappeared on its own, provided the HVAC system worked.Mold is not in most cases, bad. There are a very few strains that can aggravate existing respiratory problems, none can cause them.As I seen posted before, mold is becoming the next asbestos, chicken little type of issue.However, mold growing in portions of a house that is in good repair and of good construction, indicates the presence of higher than desired levels of moisture that can be damaging to the structure.
*i've seen and followed several mold and indoor air quality situations... all of the ones i've seen involved mechanical systems..in the public building situations.. the buildings wound up being vacated for months until a solution was arrived at...schools and town halls.. with the school committees and town councils held hostage to the demanding voters and parents.. in the commercial buildings.. the solutions were arrived at faster..perhaps because the scope of teh problem was smalleer.. or perhaps because the staff enviornmental guy's job was on the line to end the absentee problem due to respiratory distress...so.. IMHO . the mold problem is two fold... first , getting rid of the problem to stop the immediate distress... and 2d .. the lingering distrust of the public.. or customer...or employee and the tendency to blame all symptoms on the previous condition.... the problem is that the condition really does exist.. but like the anthrax scare it becomes overblown..anyone remember "legionaire's desease" ? another problem that could be traced straight to the mechanical systems...as builders we have to be responsible for controlling water source..preventing leaks and ground water..as contractors we have to make sure our mechanical subs are current on enviormental hazards..but ultimately, it is the consumer / end user who has to monitor these systems.. they need better information as to what is a problem.. and what isn't..as rob said.. mold spores are everywhere..our best bet is to not do anything that encourages their growth..... i think the industry ( NAHB for one) has to take on the mission of educating the homeowners..before this joins the ranks of asbestos, radon, and lead...
*Not to chuck a Sabot into the works, here, but if you use Icynene or similar, or rigid foam board, isn't this all moot? Assuming there is sufficient thickness of the foam, the dew point will occur somewhere within the board no matter which side of the wall is cold, and so no condensation will occur. Right?did
*"sabo-tage"to all of you non-history buffs out there, wondering what Sabot have to do with anything:The Belgian and French workers would toss their wooden shoes (Sabot) into the machinery to disrupt the German war production.And here I thought I'd never get any use out of this education...
*I learned that from Star Trek!did
*The foam board and icynene are one way to do it. Another way is to control the dewpoint of the air.The main thing to remember is that mold problems are moisture problems. If there is no moisture there is no mold, period. So you need to control the dewpoint of the air, control surface temperatures, choose materials that are more tolerant of wetting, reduce the wetting potential of the house, and maximize the drying potential.Maximizing the drying potential means never using poly or vapor barriers above grade, except in Canada and on north.I am actually going to be writing a 3-part article for our HBA that will be plain english, geared directly towards builders. Maybe I'll see what Andy thinks of it.Jeff Clarke - The main reason you don't find mold in old buildings is because the wetting potential was only a little worse than todays walls, but the drying potential was exponentially better. The walls had thousands of btus per hour going through them, which drove moisture out. The walls were ventilated and quite leaky due to outdoor air being heated up in the winter. The air that leaked out had a low dewpoint, so it often would not cause condensation. Roofs were unvented, so they were actually warmed up by the interior air that filled them. In many cases warmed to above the dewpoint of the air leaking into them. This caused alot of snowmelt and ice, but no mold. Humidifiers had not been invented, and air conditioning was scarce. Todays air conditioners actually increase the dewpoint of the air in the house. Now oversize them by a factor of 2 and you get warmer temps and humidity, even better for mold.We have all been focusing on KEEPING the water out; Instead we should have been LETTING it out.Many new homes today still have junk bath fans, no outside exhausting range hood, humidifiers, bad foundation waterproofing, open block cores (filled with floor sweepings through the register cut-outs), no vapor barrier under the basement slab, built in land that was formerly a swamp, with a barrier type “water proofing.” There is no capillary break anywhere on the foundation, so we know it will be 100% relative humidity all around the basement at best. At worst the basement floor will actually be 3 feet below the surrounding water table, the barrier foundation coating will not be 100% water tight, there is no perimeter foundation drain or it is plugged so the sump pump will not run all the time, and the block cores will have water dripping in them. In our area many jurisdictions REQUIRE a sump pump even if daylight drains are available. When I questioned it I was told that it was because a drain to daylight was “unreliable.” They just seem to work 100% of the time.Now factor in that we air sealed it, code made us put in a vapor barrier, air exchangers are "too expensive," the shed roofs are not flashed properly, there are minimal overhangs, and it becomes obvious why moisture problems are quickly becoming the norm. And without the moisture problem, there would be no mold.The one ingredient that will completely eliminate the problem is the one that most builders find too expensive, difficult, or time consuming to address.It's the water stupid!!The builders are on the hook simply because they built the thing. The rest was just mother nature.Does it sound like the builders could sue the codes bodies over stupid codes? You bet they could.Does the cost of a few more minutes of attention to detail sound more expensive than defending yourself in a lawsuit? I don’t think so.The lowest price I ever heard for a legal defense was $40,000 and the case was dismissed. How much built-in moisture resistance could $40,000 buy in a years worth of some builders houses? Around here 30 houses a year is a lot, the extra $1000 per house could buy a lot of peace of mind. The problem is that the “legal defense” and “net profit” line items in the budget are on opposite pages of the accountants’ books and are assumed to be unrelated.Sorry for the rant, getting warmed up for the article.-Rob
*Good rant, Rob. However, I still believe that I've seen a lot of black mold 'built-in' to buildings - it comes on the lumber.Jeff
*Rob,Before you write your article you do some research and find out a little more about air and Psychrometrics. Or maybe run it by an HVAC engineer for a "tech check". I understand and agree with the points you make, though we don't use the same terminology."Todays air conditioners actually increase the dewpoint of air in the house." That's not correct. Dewpoint is only a function of the moisture content and pressure of air. More moisture, higher dewpoint. No air conditioning system that I know of increases the dewpoint of air. Unless were talking terminology problems here. AC means mechanical cooling. Humidifiers do not operate in the cooling cycle, and no AC adds moisture to the air. An oversized AC cools the space too fast, but doesn't increase humidity. This creates a situation where humid air will condense on cooled surfaces. Temperature is controlled by a thermostat, regardless of the size of the equipment and unless its setup in such a way that the controls are useless, does not result in higher temperatures."The walls were ventilated and quite leaky due to outdoor air being heated up in the winter." Again, maybe we're talking semantics here, but heating air inside a space does not cause the walls to leak.BTW, humidifiers, not necessarily Aprilaire and the like, have been around about as long as dimensional lumber.
*You're right Tim, I should have said "increase the relative humidity." The problem is that the delta-T accross the coil is Lower due to wanting to get a higher SEER. They don't dehumidify as well as they used to.I have a psychometric chart on the wall next to my desk.The dewpoint stays the same, but the air has sufficient RH that it can now sustain mold growth.I should have had better punctuation in that sentence. It should read:The walls were ventilated and quite leaky. Due to outdoor air being heated up in the winter, the air that leaked out had a low dewpoint, so it often would not cause condensation.Punctuation issues fall to the wayside in a rant! 8-)-Rob
*I enjoyed your rant Rob. Too bad that so many of the laws of physics are considered to be radical and dangerous knowledge by much of the building community <>.Andy
*A very interesting thread, this one. Over the last several decades building practise has been chasing theory which has been a moving target. Now, while I possibly might have the ears of some experts here... What about vapour/ moisture/ water barriers for an ICF house? Specifically, moving from the outside of the wall inwards; a brick/stone exterior, small air space, 2-1/2" foam, 6" concrete, 2-1/2" foam, drywall interior.I would like to put some sort of barrier on the outside surface of the foam behind the brick/stone because condensation is more likely to occur as a result of the concrete thermal mass effect when warm, moist weather occurs after a cold period. Am I out to lunch on this idea or is it possible that sufficient delta T could occur across 2-1/2" of expanded bead foam to cause condensation? The house will be built in a snowbelt region of southern Ontario Canada on the north shore of Lake Erie (VERY hot and humid in the summertime.)I believe that the concrete itself will be a source of moisture at original construction, and that a membrane such a Tyvek would allow this to escape to the exterior of the house, through the foam.(Which is not an absolute barrier, as I have found by my own testing.) Foamboard can in time become quite waterlogged.I would like to use something that would be moisture-compatible that would also prevent insects from chewing away at the foam. That is, insects (carpenter ants etc.) which get by the weep hole screens or any other gaps in the stone.I expect that the door and window bucks will be sealed with canned foam.Any theories or comments on this would be much appreciated. I believe that the common practice with ICF is to use no barriers.Thanks for a fine website and a fine magazine.-Brian Smyth
*brian.... scandinavian testing disputes what you say about foam board.. in particular... EPS.. .. i used to believe that EPS would absorb moisture and degrade insulating values.. so for 25 years i used the higher priced polyiso's , and the high density Styro-SM's and Foamul-R's...so , i don't agree with your basic premise...to me , 2.5" of EPS is as much of a vapor barrier as you are going to get.. also.. at this point ..EPS is the only product i know of that can be purchased with additives to make it vermin resistant.. (Performguard).. a lot of the southern ICF companies are mfr'g their forms with PerformGuard EPS...now.... what is the best way to incorporate a capillary break in the wall of an ICF foundation or wall ?
*Mike - My evidence for saying expanded polystyrene ( EPS) is not impermeable is threefold... 1. Theoretical. During the manufacturing process the polystyrene beads are expanded in a mould by heating with steam. After they leave the mould the blocks are held in the plant for long enough to allow the steam and minute quantities of another gas (maybe pentane or butane - I forget which) to escape during which time the EPS shrinks slightly to its final size. This occurrs in a matter of days. If EPS were impermeable this would take a long time or would not occur at all.2. First-hand practical. A few years back I had a puncture in my pool cover which I "fixed" by placing an EPS life ring under the puncture hole. A few months later when I removed the ring it weighed a ton (well not quite a ton) from absorbed water. It was not held under water by any means (6 mil poly cover), but was merely in contact with the surface.3. Second-hand practical. An ICF contractor left some sample ICF blocks in the back of his pickup truck where they were exposed to rain and some puddling of water for some time. He noticed when he removed them that even the Amvic brand block, one of the densest on the market, did gain some weight, ie. moisture.Mike - I agree that EPS that's 2-1/2" thick should be a good vapour barrier, and I am aware that some manufactures of EPS beads such as BASF add borax as an insect deterrent, however, like lightning rods, no one yet has been able to provide one shred of evidence that this works. I've heard of one contractor who was working on an older ICF foundation and discovered that insects had chewed away sections of the foam underground. I see now that Tyvec over ICF for vapour reasons is probably redundant and overkill, but my thinking is that for insect resistance purposes the Tyvec might be a safer bet than say, 6 mil poly, because it's less likely to cause a moisture-trapping problem in the future.Extruded polystyrene (XPS) is much more impermeable because of its continuous, closed-cell structure, but this can only be used where sheet-type ICF's are applicable, but I've seen insect damage to this material as well.I guess my real question to this forum is "has anyone here seen any insect damage on Tyvec or similar membrane?" Or, I'm also curious- in termite regions how far below grade will termites go to enter a structure, and is 6 mil poly an effective termite barrier?Thanks for your input Mike. I'm not sure exactly what you mean by a capillary break, but below-grade waterproofing for ICF can be done by either peel-and-stick type membrane down to drain tile or a waffle-type water barrier, the latter type which will likely be used in my house.Regards - Brian.
*termites will go below a full foundation .. and XPS , polyiso.. and untreated EPS are all superhighways for termites, larvae & carpenter ants.. the scandinavian studies determined that EPS water gain , EVEN FOR FULLY SUBMERGED eps, was no more than the other types of foam...in other words.... nil.. the capillary break has to go BELOW the concrete wall or the concrete wall will wick continuous moisture up thru the wall....anyways ,brian.. the studies were enough to convince me that treated EPS would be my only choice for walls or foundations from now until someone can formulate something else that is as cost effective as Performguard EPS....
*Rob, Your rant was entertaining and absolutely on the mark. Indeed the builders have tried to sue over the building code up north in British Columbia. The code there has mandated use of poly and many feel the poly is a key factor in all the rotting that has occurred. The poly did not "cause" the problem. It's quite evident that water leakage and built-in construction moisture were the chief causes. However, the poly limited the ability of walls to remove moisture that did get in, so in that respect it contributed as a failure mechanism. I don't think builders have grounds for suing anyone re: vapor barriers, but I do think we've got to get smarter about building science (and codes too for that matter).For all those interested in the vapor barrier debate, we've been presented with two gifts in the past month. Joe L. has posted a piece on his website that discusses the damage poly can do when reverse vapor drive occurs in a wall (common at walls with absorbent claddings like brick or stucco). And John Straube has just published a paper titled "The Influence of Low-Permeance Vapor Barriers on Roof and Wall Performance." This is the best 12 pages of applied building science writing I have ever read, and I would add that its content is extremely timely. It's published in the proceedings of the ASHRAE conference held Dec. 2-7, 2001 - Performance of Exterior Envelopes of Whole Buildings VIII. These are available from Oak Ridge National Laboratory. I'll try to post a link if I can find it.
*Here are the links. For Joe Lstiburek's paper, go to http://www.buildingscience.com/resources/walls/brick_veneers_rain_sun.pdfFor John Straube's paper, go to the Thermal VIII conference website at http://www.ornl.gov/buildings/ There is a link on the left side margin for "proceedings" where you can get an order form. The proceedings cover many topics that may be of interest to those in this forum.Best wishes to you all for a peaceful and warm (and dry!) Xmas!
*Mike Steffen-interesting links.Mike Smith- are you suggesting a poly barrier between the footing and the wall? (penetrated by rebar); or pouring the footing onto poly sheet resting on the ground to form the barrier there? Have you actually put something like this into practice?Thanks - Brian.
*last foundation we double coated the footing with asphalt foundation coating..next one i'll slip 20 " strips of 6 mil poly right over the steel after we snap the form lines..
*i Maximizing the drying potential means never using poly or vapor barriers above grade, except in Canada and on north.Rob: Why is Canada the demarkation line? You also mentioned that older houses tend to be less full of mold because they simply dried faster. Would that imply that one should perhaps NOT insulate an otherwise poorly insulated older home for fear of hampering the home's drying ability? What if you were adding Central air to said home?Just as an aside--coming from a homeowner, not a builder--I too find this vapor barrier issue to be incredibly 'unanswerable'. After purchasing my 1929 house 2 years ago, I have slowly begun the process of finishing the basement. The ONE hindrance has been the vapor barrier issue. No matter who I talk to, I receive completely contradictory opinions...all of which tend to also contradict local code. I, too, would love to see and article or two (or rather, I suppose, "DEBATES") in the pages of FHB.And not to take this discussion too off-course into academia, but I'd be curious to hear if there newer, alternative home-building methods that would eliminate some of these vapor issues that exist with stud-wall construction (such as insulated concrete forms, or steel contruction)?
*(Just a feeble attempt at moving this thread to the top in hopes that this discussion will continue...I really felt it was an interesting topic...)
*Interesting and bewildering. I have an 1920's house with no insulation or vapor barrier in the walls. Not knowing code or thinking about it really, I put up R-13 Kraft Paper insulation in the exterior wall during our bathroom remodel. I did not staple it to the studs, or cover it with a plastic vapor barrier. Was this a mistake? I mean isn't some kind of insulation in the wall better then nothing? This thread has got me ready to tear out all the wall board I put up to fix it. Did I mention I live in the Seattle Washington area.
*Darrell, My understanding is that the vapor barrier issue is moot with ICF. We need to understand that frame walls (wood or steel) filled with air and vapor permeable insulation such as fiberglass have a different set of functional properties than non-frame (mass) walls or even frame walls that are filled with low air and vapor permeable insulation such as spray foam. All the quasi-science that led to the vapor barrier requirements in the first place were based on assumptions about 1) wood framing, 2) low-density insulation and 3) the strange belief that somehow walls only get wet from one direction, and then only dry to one direction. Often our walls do not fit the first two assumptions, and very rarely do they fit the third.You asked about alternative walls that eliminate the vapor issues. Try this one: 2x4 wood wall (studs at 24" o.c preferably but 16" OK where you need it), plywood sheathing, full peel and stick membrane over the plywood, 2-3" of XPS rigid foam (blueboard) over the peel and stick, then 1x3 p.t. wood furring installed over the foam (vertically along the studlines), then siding of your choice (some siding require 16" o.c. framing). Did I forget to mention, no batts in the stud cavity, and NO vapor barrier at the inside face of the wall, just a couple of coats of latex paint. Now this wall is moisture tolerant! (it can dry/"breathe" completely to both sides as interior or exterior conditions allow...) There is no place for moisture to get trapped, and really, there is no place for condensation to develop other than at the exterior face of the peel and stick, where it doesn't matter because this is your drainage plane. Or perhaps within the rigid foam, but again this is outside the drainage palne and XPS foam is moisture tolerant. The whole wall r-value very closely matches a 2x6 wall with R-19 batts. Admittedly this wall will cost more, and has its own set of technical issues that one needs to be concerned with, but it is bulletproof from a moisture standpoint. The real beauty in this wall lies in the peel and stick, which functions as a combined vapor/air/weather-resistive barrier.
*mike.. that's an interesting wall.... but i don'tthink i would like to build it...the exterior details would drive me crazy... foam like to crush.. especially around framing hammers.. so you need full blocking at all key locations...like every door.. every window...cosners... cornice trim...we used to do exterior foam.. but no more..have you developed a technique for dealing with some of these issues ?also.. lots of studies say OK, eliminate the interior vapor barrier.. especially if you are using cellulose, which will pass moisture to any direction that is drier...assuming that to be true (which i do)... why wouldn't you fill the stud bays with cellulose?
*Mike, We have not built this wall type with wood framing, but are about to begin construction on a 15-story apartment tower utilizing the same concept only applied over steel stud framing. I had heard of the concept and loved the logic behind, that's why I think its worth putting on the table even with wood framing. Just north of us in Vancouver BC, a number of wood frame buildings have been built this way over the past few years. Perhaps we can get someone to chime in on the details. You are right, they might drive someone to insanity. Chris Makepeace is in Alberta I think and he has developed this type of system for many years. Here's a link to a brief article on it: http://homeenergy.org/archive/hem.dis.anl.gov/eehem/99/991108.html I think your comments on the cellulose fill are right on. That would be something to consider closely because there would be quite a bit of wetting of the cellulose in cold climates (the dew point at many times would be in the cells). Of course, the cells could then dry to the inside if no vapor retarder as you suggested. Probably would work (and work well), but you'd want to look at closely, given the specific location/climate. One concern is if using drywall the backside of the board might get excessively wet at times. One of the beauties of the all exterior insulation wall is you know that dewpoint is always outside of the wall cavity and that the wall cavity is warm and happy!
*Mike and Mike, I am learning, so bear with me.I keep reading that at some point the dew point will transit through the wall cavity. I thought this was a cooling climate problem, but now you are saying it is also a heating climate problem?My understanding is that heat "flow" is from warm to cold (higher energy state to lower). Insulated walls retard this heat tranfer, but are not 100% effective, so each wall system ends up with corresponding u-value. Now here is where I get lost.With a high enough R value (low u value) system, how does the dew point transit the wall faster than the heat loss?Educate me please. I think I am getting confused. i know what dew point is, so just explain the transit phenomenon.Dave
*DaveIn a real wall system you have many materials so it can be a little confusing. But lets look at a very simple "wall". One of 6" of concrete and one 6" of foam. No other materials.In both case you will have heat energy flowing from the hot side to the cold side. The material and (thus the u value) determine the rate of flow. But in all cases you will have a gradient across the wall.Assume that it is 70 inside and 10 degrees outside for a 60 degrees difference. 1/4 of the way into the wall it will be 55 degrees, 1/2 40 degrees, 3/4 25 degrees.One wall might be losing 1 btu/sq ft - hr and another might be losing 25 btu/sq ft-hr. But they will have the same gradient.So if you have air with a dew point of 40 degrees and it "gets" in the wall in the middle you will have condensation.Now in almost any real life wall you have many layers and each have different u values so it is not that simple. But the effect is the same. You will have a gradient across the wall, but it will not be uniform. And by using different materials with different u values you can control in which layer the dewpoint falls.
*"You will have a gradient across the wall, but it will not be uniform. And by using different materials with different u values you can control in which layer the dewpoint falls."And, I assume, the goal is to have the dewpoint fall in a layer that has minimal-to-no air flow (ie, the middle of the XPS, for example) correct?Going back to the vapor barrier issue, I see the biggest problem would be in climates that are extremely cold in the winter and extremely hot and humid in the summer (southern MN, for example), where the cooling/heating sides of the walls completely flip-flop with the season. Is that a fair assumption? If so, then, ideally, you'd have a vapor-barrier on both sides of the wall, which of course, is a bad idea unless you can guarantee a 100% air-seal...which you can't. Which makes that XPS on the outside wall all that more appealing...
*darrelI am not a building pro, but I am electrical engineer (by training, but now do software). So I am experienced in solving problems like this, but not this specific problem.so I am not going to embarres myself with given you more details that I know.But a couple of the items envolved or how much condensation that you have and how can you get rid of it.While you might have a potential moisture problem both summer and winter the summer problem will only last a few weeks, while the winter problem last months. You might want to look at http://www.buildingscience.com/housesthatwork/default.htmI see that they have lot of their stuff on line and you can try different climate.
*Thanks Bill. I thought it was something like that, but did not understand the gradient concept.This explanation makes Mike Smiths' wall systen look even better. His wall provides a low perm barrier on the heated side of the wall, with a higher permeable insulation in the wall cavity. His sealing method of the rigid foam probably does a better job as vapor retarding membrain than most poly I have seen installed. Since we know that there is air movement within the wall cavity, due to the temperature gradient, where might the dew point acctualy be?In my area I have to be concerned with both heating and cooling application of any design system. Our RH in the summer can get into the 90% range. That becomes a big concern if the dew point gradient is in the last 1/4 to the inside of the wall. winter condition aren't as bad as long as we keep the RH inside the hone at about 40%. Outside cold air for the most part is pretty dry <40% RH.I guess we are seeking the best balance for both applications. The design for my new home calls for Exterior Insulated Finish Systems(Stoe, or Drivit).From this discussion I am begining to picture a "drip line" somewher within my wall system. Not good for my peace of mind.
*Arrgh. That was a brain crippler. I'm finishing my walk out basement and am now thinking I'll just paint the insulation and wait ten years to hang the drywall. Maybe a new einstein will appear and solve this issue by then. Thanks for the info and debate, but I think I'm in worse shape for all the knowledge-simple home owners need a little assurance from the big brains sometimes (can't we all just get along)
*[quote]I'll just paint the insulation and wait ten years to hang the drywall.Ha! That's what I've been thinking.Actually, we just took a tour of an open house where they had a fully-finished basement. The outside walls were block with plaster applied directly to the walls, then painted. I'm sure the heating bills went up, but there wasn't any worries of a vapor barrier.
*Dave... in actual practice... foam in Northern climates on exteriors has worked fine and may actually be less of a problem of having moisture in the wall. The fiberglass in the wall will be warmer this way from inside heat and hense have less water in it. foam on inside walls will leak somewhere. Where it leaks will be exposed to huge amounts on infiltration...lots of moisture cooled by outside air temps rapidly enough to get lakes of water forming... Many factors come into play... thats why there is no definitive right way that we all build to. I like the idea of less barriars being best. I like the idea of walls being able to dry. I like the idea of SIPs but not the idea of failed SIPs. Cellulose dense packed has survived so far as I know.. and with out VB as done by some.Draining and drying... is good... double barriers or more... is bad.near the stream,aj
*John Straube's paper on vapor barriers, previously mentioned in post #63 above, is now online for your viewing pleasure: http://www.buildingsolutions.ca/Downloads/ASHRAE%20Thermal8%20Vapor%20Barriers.pdfBe interested to see what you all think of the issues he raises...
*Dave R., You said "Since we know that there is air movement within the wall cavity, due to the temperature gradient, where might the dew point acctualy be?"I do not agree with what "we know". Air movement through the wall is independent of the temperature gradient. Energy transfer through the wall is driven by temperature difference, not air movement. Air movement is driven by pressure differential. It is entirely possible to have an impermeable wall that transfers heat. From my point of view, I am not a builder or building scientist, control of air movement would be better addressed by control of the pressure inside the house.It seems to me that a vapor barrier, that is not air tight, does little to prevent wetting but is good at retarding drying, causing more harm than good.
*Tim...i It seems to me that a vapor barrier, that is not air tight, does little to prevent wetting but is good at retarding drying, causing more harm than good. This is my view also...near the stream,aj
*Tim,you are correct if you assume that you have an air tight barrier on at least one side of the wall. In actual practice, I don't think I have ever seen that achieve. Any unsealed penetration will cause at least some air movement because of the temperature gradient. Cold air is dense air no matter where it is, and it will settle,and the warm air will rise.In a perfect wall the gradient would manifest itself from warm to cold both across the wall, and from top to bottom. The rate at which all this thermal activity takes place is what we are trying to control. The moisture content of the air then becomes another factor as I have learned from all of the above.I am becoming a convert, not only from you guys, but every thing else that I am reading. You guys just might be "preaching to the choir" before long.So, now correct my "fuzzy thinking" about what I just posted:>)Dave
*Dave,I may be nit picking, here, but whether the wall is air tight or not, a temperature difference will not cause air movement. There a two circumstances that cause air to move: a driving force (i.e. pressure difference) and a flow path. True, warm air is less dense than cooler air (at the same pressure and humidity) and the difference in temps indirectly causes air movement. But what actually happens is, the temperature causes different densities and that results in a pressure gradient that causes the flow.If I had a house in which I could control the relative pressure, I could cause air to leak into or out of the space, regardless of temperatures inside and out. To that end, a smart ventilation design would be able to create a slight, controlled negative pressure during the heating season, causing cold, dry air to leak in; and a slight positive pressure in the cooling season causing cooled/dehumidified air to leak out. If someone created such a house (or any other type of building for that matter), this entire issue of whether a vapor barrier is good or bad (or is required or where it required, etc.)would not exist.
*Tim & AJ, I'm with you guys as well. You hit the nail on the head. Perhaps the only other simple distinction to add is that low-perm vapor barriers should only be used where they reduce wetting (by vapor diffusion) more than they reduce drying (by vapor diffusion). To my knowledge, that would be at buildings with very cold exterior climates or very humid interior climates (i.e. swimming pools, etc...)I think the link I posted above may not be "linking" (it didn't for me). Try http://www.buildingsolutions.ca. You'll find some good ideas presented there that relate to this discussion.
*Hugh White has waited 157 days for this very important answer to his original question....Hugh, I don't know!I do know this was a great post. I'm exhausted from reading it. Breaktime is how I watch sappy movies with my wife. She watches the sappy movie and I sit on the couch next to her with my laptop and catch up on the latest exchange of ideas. It's a win win situation!Thanks guys.
*Dow makes a new housewrap that keeps moisture out but also says that it allows moisture in the walls to escape. I saw some at the mohegan sun home show in ct last week. Its pourous looking but when I picked it up to blow through it, I felt nothing on the opposite side. It also has a tacky feel to it which helps it set on the plywood to help you nail it up. Same sizes as tyvek. Wouls the installation of thin furring strips under my white cedar pine siding help the wall breath better? After reading this hole thread, and half the links posted, it seems a breathable wall is best. If it gets drafty, I'll just turn up the heat.
*Link to dow housewrap http://www.dow.com/styrofoam/na/dowpro/new_hr.htm
*Whalemania,Thanks for the link. Except for the thermal insulation properties it sound like one of the original adds for tyvek. I could be wrong. That has been a long time ago, and I do have crs.This sounds like what could be called a semi-permeable membrain. A material that passed vapor in only one direction.Now does anyone else know of this product in use?Dave