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Old 04-25-2012, 11:03 PM   #46
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gary: " I would use a "stucco" housewrap against OSB because it dries so slowly. Especially between OSB/foam board." Did you leave out a "not", or did I misinterpret what you said? It sounded like you wanted a housewrap that dries faster than "stucco" housewrap, but then you said to use it. ???


Last edited by jklingel; 04-26-2012 at 07:04 PM.
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Old 04-26-2012, 05:54 PM   #47
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For house wrap to be used as an air barrier there are rather strict instructions that the manufactures put out that must be followed. I have not yet seen the method used in full but that may be a regional thing. Even when that method is used it is greatly compromised once all the holes are put in it for fastening sidling. I believe that hose wrap as an air barier is nothing more then a marketing tool. This is why I consider it very important to have the structure be air tight from the outside. There are many ways to do this with out having to use caulk at the seams. However keeping the outside air out of the wall and the house air out of the wall are both very important to keeping the wall dry. I keep saying it and I will say it some more that you will have less plywood swelling because you caulked the gap that was initially mentioned. You can not use the drywall to stop the outside air from entering the home. This is the wrong place to stop the air. There is no reason to have 5 plus inches of insulation in the wall if you aren't going to give it a chance to do its job. If you are going invest in an insulation in the wall to help with air movement it might as will be spray foam. If you stop the air on both sides of the wall there is no air moving in the wall to try to stop.
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Old 04-26-2012, 07:14 PM   #48
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im starting to think this is a joke.

housewrap isnt a marteting ploy. its expected on all new homes unless replaced by product that can perform in a like manor. its proven to keep moisture out and improve the energy efficiency of homes. its required by code.. home inspectors dont get a cut of the profit of house wrap sales...

im curious as to what your background is regarding construction
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Old 04-26-2012, 09:29 PM   #49
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I questioned house wraps ability to be an air barrier and you assume that I want know paper on the house at all? Are you suggesting that there is no other reason to put house wrap on beside to stop air flow? I always put tyvek paper on when I am doing a do it myself project. I said house wrap as an air barrier was a marketing tool and you turned that into house wrap in general is a marketing ploy and implied that I thought that inspectors might be in on it. House paper has a lot of competition and the more they convince people that they are in on the movement to keep homes air tight the more secure their future is. I am gathering from my brief time in DIY chat room that their efforts are paying off. There is a large shift in how people are building as is applies insulating and air sealing. The producers of building products know this and are trying to get their piece of the pie. I apologize that I have presented myself in a manner that has brought my background into question.
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Old 04-26-2012, 09:37 PM   #50
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Kirk and Hart: you are on the same page, as far as I can read. "Air seal, insulate your gonads off, and use Tyvek for a WRB." Cheers.
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Old 04-26-2012, 10:57 PM   #51
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Quote:
Originally Posted by jklingel View Post
gary: " I would use a "stucco" housewrap against OSB because it dries so slowly. Especially between OSB/foam board." Did you leave out a "not", or did I misinterpret what you said? It sounded like you wanted a housewrap that dries faster than "stucco" housewrap, but then you said to use it. ???
------------------------

Good catch. It was late, I ran my thoughts together without punctuation, here: "I would use a "stucco" housewrap against OSB (because it (OSB) dries so slowly)." I was referring to the BSC article below.

OSB doesn't breathe/redistribute water as good as plywood, it is hygroscopic. Fig.1b; http://www.buildingscience.com/docum...d%20in%20walls

You need a gap because OSB composition wets the wood chips lineally (hence the strength axis)- and "grows" in length/width, not area contained as plywood (wetting the outside/inside faces close to water source). Another reason not to seal the gaps (other than all manufacturers suggest), with them exposed; the OSB will dry sooner, especially through an untreated field-cut edge/end.

OSB is much less forgiving than plywood as it is very slow drying and stores the water inside longer to rot.
Relative Humidity-25% osb-1.25 ply-0.89
RH- 75% osb-6 ply-14
RH- 95 osb-24 ply- 49
With plywood, the wetter it is the more permeable (open) to water. You want the high numbers with the high humidity.
Because OSB takes so much longer to dry than plywood, there is a good opportunity for mold growth. It is acting as a vapor barrier; “There are more differences in hygroscopic properties between OSB and plywood and fiberboard, especially the vapor permeability and moisture diffussivity. As shown in Table below, the value of vapor permeability of a OSB board is one magnitude less than the wood and much less than that of the plywood panels. Using of OSB as wall sheathing is essentially adding a vapor barrier at the outside layer of the envelope in addition to the inside barrier.” Compare what I used BOLD on above to the chart- twice as hard for moisture from inside to leave(vapor permeability) and ten times less diffusivity than plywood; http://alcor.concordia.ca/~raojw/crd/essay/essay000129.html

I've used OSB on about 300 houses (since early '80's); walls, roof, and floor. I always gap it with a 10d at install and 2 days to 2 weeks later, the gap is gone, depending on humidity. Edge swell on roofs is very noticeable: http://www.gp.com/build/PageViewer.a...elementid=6132

OSB dries out on the face without the wax coating (to keep sheets from sticking to each other in manufacturing), and at the ends, edges. Especially if the studs, plates or OSB was damp or wet during/before construction. Then as the framing dries out; shrinking, leaving gaps underneath the OSB for air to pass there. In a house, with the natural stack, wind and forced air pressures (fans), you would get more blow-by at those connections. Remember OSB wets and drys in the many layers of chips, from one to another as B.S.C. brought out. Also with the three densities (and permeability) of material in OSB as the other site said, drying at the seams would help. Especially with wet/dry lumber created gaps, because the sheet goods will stop air everywhere but the seams, being forced in or out by the house pressure. Cover them with a vapor open material, rather than waterproof material to give the OSB that 1/8" gap = 7/16" X 24' of edge/end seams for needed extra area to dry if it ever gets wet, yea-right... caulk them on the inside for your sheathing air barrier as I explained earlier.... and ADA to stop interior air to the cavity.


Interesting: OSB w.Tyvek (58 perms) takes 12 days to dry after wet;

Typar (16 perms) takes 40 days, encouraging mold- pp.15, Fig.15:

http://repository.tamu.edu/bitstream...pdf?sequence=4


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Old 04-26-2012, 11:51 PM   #52
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Gary: Got it. That makes sense now. Re :"Relative Humidity-25% osb-1.25 ply-0.89 RH- 75% osb-6 ply-14 RH- 95 osb-24 ply- 49 " Are those perm ratings? It sounds that way. This further plants my heels: I see no reason to use OSB.

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