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Is Tyvek necessary on the outside and poly. on the inside for the following wall design? This will be in a cold climate. The wall insulation is solid foam in place polyurethane with standard drywall and sheathing. Thanks.
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Short answer: No. Long answer: as I understand it, polyurethane (as opposed to icynene) does not require a vapour barrier on the inside, and of course no air barrier would be needed since sprayed-in-place foam seals all the air leaks and Tyvek is meant to be an air barrier, which you don't need. I'd install a 6 mil poly vapour barrier inside anyways just for fun, though...
*No Poly, no no no.Double barriers are double trouble.J
*Only install the poly if you want to open up your walls in a few years to replace the studs, plates ect...ect....
*I beg to differ. You can't get condensation on poly that is the same temperature the inside of your house. But leave the poly out then, if it makes you feel better. Think about it... hang a pice of plastic on your wall... now, hang another one against it... see any water forming in between them?
*Ross,Double plastic with moisture involved is reinventing the sponge!!!!Put two pieces of plastic in an enviroment that has condensing moisture and it will fill up with moisture between the layers...b I forgive you for you know not what you are talking about....Oh and you are also invited to the b Fall Fest....Slaps...beer and all!J
*Let your house breathe for pete's sake!Blue
*Moisture cannot condense on a surface that has the same temperature as the inside of the house... but why are we arguing about this anyways, you don't need plastic over polyurethane foam... but let's just call it something else, like icynene, or Roxul, or fiberglass.... what makes you think there would be condensation on the vapour barrier on the warm side of the insulation? It's done all the time, unless you folks don't believe in vapour barriers (there are such unfortunates, they're the ones who think houses need to breathe). I could pull out all my credentials and dazzle you with all the certificates and courses and licenses from the past 20 years that says that I do know what I'm talking about, but suffice it to say that I'm pretty knowledgeable about energy-efficient houses, thermodynamics and building science. Not that I know it all, but when was the last time you had condensation on, say, your computer screen, which is the same temperature as the air in the room. Now look at your cold beer bottle... ok, you don't need to be an expert to know that there has to be a colder surface in order for condensation to form. So leave out the vapour barrier over polyurethane if you want to, but I was simply stating that despite the claim that urethane does not need a vapour barrier, the permeability of polyurethane, particularly where the skin has been shaved off as it would be wherever the cavity was overfilled, is significantly less than poly, and I would avoid having diffusion of water vapour into the insulation and being trapped behind the less-permeable plywood by installing a layer of poly on the warm side of the wall. The warm side... the one that is the same temperature as the room... like your computer screen... the one that doesn't have water running down it right now. There is no water condensing on the warm side of your insulation, believe me!
*Ross,If two Vapor retarders are better than one...lets just add a dozen....and while we at it lets wallpaper the b*tch with your credentials....b We're sure to meet at Fred L's Ventless Tent seminar....in the mean time I might have to email a slap to you if Joe could tell me how to do it graphically.J
*Ok, then better not use oil paint on your drywall anymore, it's a vapour barrier you know, you could get moisture trapped between the drywall and the poly. Thanks for pointing out how stupid it was of me to get in a slapfest with ya. And don't overlap your poly anymore at the joints, you'll get water trapped between the two layers.
*Ross,I don't use no stinkin Poly no more.b In the Badlands and Rebel to the grave.J
*Oh oh,Ross must be new to this board!He's starting it all over again.Hav'nt we been through this a gazillion(spelling anyone?)times?Ross,you state that moisture will not condense on a surface that has the same temp. as the inside of the house.So why use a VP if the inside surface of the wall is the same temp. as the inside air?I'm with Blue on this topic,let the house breathe.I think we should all use my house as a model example for new construction.What do you guys think?(heh,heh,heh)
*ummm.... gee, would the purpose of the airtight vapour barrier on the warm side of the wall have anything to do with keeping the humid warm air inside from condensing on the cold surface on the opposite side of the insulation? could be a stretch for some people's imaginations, since they're not physically connected in space, that inner warm layer and that outer cold layer way on the other side of the insulation... oh, what the heck, you win, I quit, we build them all wrong here in Canada and the R-2000 program has set building science back to the stone ages...
*RossFellow Canadian. Buddy. What ya gotta understand about these poor Americans is that they just can't fathom the fact that the suprinsulated plastic bag called the Sakatchewan Conservation House, not only hasn't rotted out like it's American peers, but it is also ridiculously i energy efficient!!Their poor egos can't deal with that so they have to invent a whole new system to hang their hats on. . . it's what they do!!!Three important points to remember when dealing with our wonderful (I mean that sincerely guys) neighbours is that not only is their F/g inferior (they're still using that Kraft backed junk that went off the market here 20+ years ago, although they are now producing some sort of higher density stuff) and they still can't figure out how to install a leak proof air/vapour barrier-vapor diffusion retarder (or whatever they're calling it this week). Also they are wedded to cellulose. . .and with good reason. . . ever see the amount of newsprint in the Sunday New York Times??? Mutiply that times all their other verbose newspapers, and their 200 million+ population and you've got a recycling paper/blue box nightmare!!! Ease up on them, they're doing the best they can with their limited resources. . . it's why they're always after ours!!!Sorry Jack 'n Joe, it's hard not to write a novel when my tongue is planted so firmly in my cheek!!!i Intoxicated by the exuberance of my own verbosity-Patrick
*Intoxicated by your own verbosity? I think I caught a bit of a buzz on that one too :-)R-2000 since 1983 and proud of it
*Ross,Glad R 2000 has been "very, very good" to you and all your fellow Canadians...We'll set up a Canadian tent at the Fest for Demonstrations...Fred L will be scheduled at the same time to keep all from heckling each other to death...That's a seperate show in itself and the tickets are gonna rock!!J
*JACKWill that be the i TAUNTIN' tent??-P
*Nice of you to set up a tent just for us Jack, But could we call it the beer tent.
*All tents will of course beb "Dual Purpose."b "Drinking, While I Drive....(Saves Time)...Forget the Lives!!"b Less is More!!....(Less lives, more beer for the rest of us!)J
*Adirondack. We've been using double vapor barriers [sic] for years and years. And we've built millions of houses with double vapor barriers[sic] without any recorded failures. GeneL.PATRICK. As long as you don't become a sesquipedalian.Remember the archiologist in the Doc Savage magazines? GeneL.
*Hi GeneToo many syllables there fer me, LOL. . .don't know the Doc Savage mag! While you're here. . .something that I've wanted to ask: could you explain how a 'Leger style' house can maintain it's interior temp. while, presumably, fully exchanging interior air at least 6 times/24 hrs. on (I think you stated some months back) about $35. per month for heating? You have stated that you're not into i massand don't find HRV's cost effective?If the answer is i tooobvious you can i slapme at the i Fall Beer Fest( maybe jostling with Fred for 1st dibs). You are coming to the 'Fest' aren't you. . . it would be a short drive, I assume???regards-Patrick
*b To all of our northern friendsAs a educated redneck I would like a little help in helping to understand what you're talking about in terms that we all can understand. We're not looking for pieces of paper to hang on the wall(if we have to go that way I'll match up one for one with you)and if you want to start with savings we can do that. we have done a lot of older rehabs and we track what we do and stand behind what we do. I'm not tring to be a smart assjust want to have your position stated clearly.
*Educated redneck... that's called an oxymoron here in Lanark County! I think we're getting new construction and remodelling confused here a bit, we'll put in an air/vapour barrier in walls we open up in renos, knowing full well there's no point in it as long as the rest of the house is full of holes. There's no energy savings to be had even putting insulation in one little area while the rest of the house is uninsulated, but we do it anyways because it might make that one corner a bit warmer than it used to be (yes, it can be warmer in one room and still not save you a cent on your overall heating bill, but let's not do the math and say we did). Maybe someday when the rest of the house gets done right they won't have to tear out and redo our work, but who knows... who cares... I just do this for fun, anyways. But in new homes, in cold climates, you're better off sealing the house airtight and then ventilating conciously, rather than letting the wind and temperature differential do it for you. A house that "breathes" will breathe a lot more on cold windy days than when the inside and outside temps are the same and there's no breeze, and you'll just love those molds growing in the walls. When it gets -30F, I'd rather be warm, if I want to feel the wind blow I can step outside! Someone on this board put it right when they said "Common sense is just genius in working clothes". Those old faded pieces of paper don't mean anything, with a memory deficit like mine, but I try to make up for it by learning all I can and keeping an open mind. By all means leave the air/vapour barrier out altogether, if your codes allow it. On the other hand, you could just admit us Canadians are all perfect and believe everything we say :-) (cringing in the corner awaiting a good slap)
*0k Ross we agree on one thing that what ever we're doing we want to do the best that we can. Even if I only open one wall I'll improve on what's there but not at the cost of doing greater damage.If you could explain further about using poly for a vapor barrier on the inside wall it would be a great help. I'm always trying to learn and always try not to be the one stuck in the mud.You are free to use my grandfather's quote when ever you need to.Their's no need to stay in the corner I'm big but I'm nice(sometimes)
*As I recall, the top of the "Sakatchewan Conservation House" (sic) is insulated with cellulose.
*Gene,What are your double vapor barriers....not foam and poly and exterior tyvek I bet.J
*Patrick. The ANNUAL heating for the Leger House was THIRTY-EIGHT--$38.00.I posted a long response to your statement that I am dismissive of mass.I wrote that I'm not so much dismissive of mass as opposed to the hype about mass. I then went into a long discussion about a house's Time Constant (TC): the time it takes to warm-up a house and once warmed-up how long does it take it to cool off? Ergo, a house with a long TC would take say, 8 hours to drop two degrees, or 3 days to drop 18 degrees.A TC is a concept from electronics, called an RC circuit. The R is for resistance and the C is for capacitance. TC=RC. However, a house can be seen as an RC circuit because it has Capacitance which we call mass, and it also has resistance (R). now the TC is directly proportional to the product of RCR: TC=RC. Now there are two way to get a TC: TC=rC--note the lower case r, and TC= Rc, again note the Upper case R.The time constant of a solar house is TC=rC. Forget the insulation and concentrate on mass and glass. A MESH(Micro Energy Sysyem House)house's TC= Rc. Forget added mass and concentrate on insulation and air tightening. Of the two ways to achieve a TC, insulation TC=Rc is the most effective and least expensive way to do it.Comp;are, for example the performance of the Kelbaugh house in New Jersey.It has an all glass south wall behind which is a Trombe wall named after a Frenchman who didn't invent it. The 46 foot long south wall of the Leger house had *80 to 100 square feet of south wall glass, and no Trombe walls or added thermal ass...unless you wan to make an issue out of the 2nd layer of gypsum board on the exterior walls.Yet the Leger House runs circles around the Kelbaugh house performance wise.According to some building scientist an R-19 2x6 wall with 1-inch of RFBI on the exterior, and two layers of gypsum board on the interior is as effective as a masonry block wall with plaster on the interior and 2-inches of RFBI on the exterior.The introduction of RFBI insulations made a big difference in hot dry climate construction. Placing RFBIs on the exterior of a mass (CMB)protected it from heat gain during the day, thus making 2 foot thick adobe and rammed earth walls unnecessary. If you believe HRV manufacturers every American house. regardless of climate must be equipped with a HRV. I posted a long article on determinimg the cost of owning and using an HRV. A cost analysis must be done befor buying one.Agsain the problem is with the hype. Hope this answers your questions Patrick.Adirndack Jack. My statement is abit misleading. OPbviously I did not build millions of houses with double vapor barriers[sic]. I should have said the nation constructed millions of houses. The double vapor barriers were and are exterior plywood and interior polyethylene VDRs. According the the NSHB Research Foundation there are no recorder repoert od failures because of the plywood on the wrong side.GeneL.
*Gene,you're a technical kinda guy, so I'm surprised that you would think plywood the way it is installed and leaking air like a sieve would qualify as a rot promoting second vapor barrier....It doesn't fit my profile of a problem install for two reasons....One the two barriers aren't touching, creating a capillary sponge...and two as I mentioned, way to(o) leaky.I work on remodels that when walls are opened I find nothing but rot...Last job had to do with a million plants and the water kicked off by them....Users of homes create just as many problems as the method of construction....My idea is to build homes that are resistant to user's destruction and are affordable...On the Weatherization Warpath,J
*GeneSorry you felt you had to reiterate your excellent explanation of house TC. I had read that carefully, and also remembered your previous post about the cost effectiveness of HRV's. . . I only mentioned the two details of i no "extra" mass and no HRVto setup the question of and how you achieved air changes over a 24 hr. period without suffering more significanti heat lossthan the $38/yr.heating bill would imply? I'm still somewhat baffled. . . i " a house with a long TC would take say, 8 hours to drop two degrees, or 3 days to drop 18 degrees."is this assuming normal comings and goings through exterior doors, planned air changes, bath and kitchen venting???. . . and if so, why isn't there heat lost in warming up the replacement air which should be i completly changed at least 6 times a day. Curiously=Patrick
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Is Tyvek necessary on the outside and poly. on the inside for the following wall design? This will be in a cold climate. The wall insulation is solid foam in place polyurethane with standard drywall and sheathing. Thanks.