# caulk sheathing??



## ratherbefishing (Jan 13, 2011)

Hi all.
I'm just about done sheathing my addition with OSB. I nailed up the OSB horizontally, with a 11" filler strip in the middle. There are a few small gaps, maybe 1/4' or so. Probably caused by my inability to cut a straight line. House wrap is going on next. Should I caulk the gaps? If so, with what?

Thanks!
Mike


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## kwikfishron (Mar 11, 2010)

No, you do not caulk the sheathing but the horizontal seam should be blocked and nailed off to achieve full perimeter nailing.


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## Just Bill (Dec 21, 2008)

It would not hurt to cover the seams with tape before installing housewrap.


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## Gary in WA (Mar 11, 2009)

Wrong gap to worry about; http://www.buildingscience.com/docu...nd-the-gap-eh/?searchterm=foam board in walls

Gary


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## HartKyle83 (Apr 22, 2012)

*caulking joints*

IF you are not going to use spray foam insulation I would highly recommend caulking such a gap. Granted you do need blocking to seam your sheathing together four feet in from each corner. Fiberglass insulation does not stop air flow. This means that if air can enter the wall the insulation is virtually useless. It has no ability to stop cold from passing through the wall unless it is sealed on all six sides. Once this is accomplished it is fairly effective. I would recommend caulking as many gaps and joints as you can. It really doesn't take that long.


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## woodworkbykirk (Sep 25, 2011)

do not caulk the exterior sheathing.. not only will you be creating a vapor barrier on the outside of the house which reduces the framings ability to breathe to the outside but it will also reduce the sheathings ability to swell if it does take on moisture which will cause it to buckle

wall sheathing is expected to have a minimum gap of 1/8", some inspectors have been known to expect a 1" gap where the framers had to go around and cut that size gap after the fact


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## HartKyle83 (Apr 22, 2012)

Every thing i have been learning as of lately has been steered me in the direction of sealing up all the gaps. The school of thought that I have come to agree with teaches that moisture tends to ride in on air through gaps in the structure and wood is not a vapor barrier. This means the more you seal the wall the drying it will remain and filling the gaps does not turn the wall into a vapor barrier. I have had many building inspectors encourage sealing the wall and have not had any who had a problem with it. Here is a site I found that mentions a few such things http://www.co.monterey.ca.us/buildi...-20-HERS-BuildingEnvelopeLeakageTestRev07.pdf. Here is some info for requirements on habitat for humanity houses http://www.builditsolar.com/Projects/Conservation/opcaulk.pdf. I have been to several classes and seminars that all teach what I have mentioned and the building codes are all getting on board with it. What code book is it that requires these large uncaulked gaps in the structure?


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## Tom Struble (Dec 29, 2008)

interesting Hart,you don't feel using an air barrier to be sufficient?


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## HartKyle83 (Apr 22, 2012)

I am not sure that I know what you are asking? All of the components together are the air barrier. Its about limiting air exchange which requires a lot of different techniques through the entire building process. Some of it has to do with where you are. I live in northern IL and it get cold. I learn more from Wisconsin which is just an hour away and they are way ahead of there time. If you are in a more moderate climate some of these techniques may be overkill.


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## Tom Struble (Dec 29, 2008)

i meant a taped wrb,which would be considered an air barrier


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## HartKyle83 (Apr 22, 2012)

I think that helps but there is a specific way that house paper has to be installed to stop air and I have never seen any one install it that way. The bottom of the paper is almost never addressed and then thousands of holes are put in the paper to attach it and the siding. I think this is important but not the answer.


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## Tom Struble (Dec 29, 2008)

i agree,thanks for the discussion:thumbsup:


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## jklingel (Dec 21, 2008)

Caulk the exterior plywood (don't use OSB unless it is THE BEST stuff made), but caulk it w/ flexible caulking between the studs and it. Leave the gap for the ply to move if it has to, and tape over the gap. That way, you get the air sealing you need and the gap that some people say you need.


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## Gary in WA (Mar 11, 2009)

Hart, your first link addressed caulking between "conditioned and unconditioned" areas, not uncod. to uncod. as in sheathing gaps. The second link caulked sheathing gaps, contrary to OSB info- "Moisture protection" and "Reminder" - when paint/stain is fine for treating field-cut edges, but leave the required 1/8" gap all around the sheathing for expansion/contraction. You don't want material in the gap: http://www.ewpa.com/Archive/2006/aug/Paper_266.pdf

Much better to stop the air leaks to the wall; from the inside- at the drywall; http://www.buildingscience.com/documents/information-sheets/air-barriers-airtight-drywall-approach/
and from the outside; caulk the sheathing/studs/plates joint from inside the cavity before insulation. 

Gary


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## HartKyle83 (Apr 22, 2012)

GBR. I agree with all of the info in the articles you linked. I do not agree that you stop the air at the drywall. The drywall is where you stop the warm moist air from the inside of the home from entering the wall not the cold outside air from entering the home. Why would you allow cold air into the wall cavity from the outside putting the cold air right on the back side of the drywall. Stop the air before it can get into the wall and let the insulation have a chance to do its job. On the topic of allowing a gap for the plywood. I would never build a wall that had a 1/8"gap that was not spiting on framing. If i was not going to install framing for it to split on I would prefer to see a caulked gap then an open gap. If you build with dry lumber and keep the air out you reduce the moister content of the lumber in the structure keeping it from swelling. In the instance it did swell it is the result of an actual leak and in that instance having an open gap in the walls or a caulked gap will not make a difference. I would actually think it would be better if it was caulked so the water didn't get to the gap and get in the vulnerable edge of the plywood. The water might drain down the entire wall. Keep in mind in the real world plywood never has an 1/8" gap all the way around it for obvious reasons. That can be protocol all day long and it never happens and every builder and every inspector knows that.


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## HartKyle83 (Apr 22, 2012)

I just wen back and looked at my links. I think you need to rethink what you said about the situation we are looking at being unconditioned to unconditioned. That would be an attic or an unheated garage. The inside of the wall does not count as an unconditioned space. It is the barrier between the conditioned and unconditioned space and the link I posted is calling for the gap to be caulked or foamed.


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## woodworkbykirk (Sep 25, 2011)

any building inspector ive ever had alwaysa looks for the 1/8" gap in the plywood or osb. its expected here as per building code and per the manufacturers specs. the do not want hte gap caulked its supposed to be open.. the installation of a air barrier is what stops air movement. the air barrier can be either type 2 foam or house wrap (tyvek, typar). i know carpenters that have installed sheathing tight toghether only to be made by the inspector to either remove and reinstall it or cut a gap in it. when it does get wet it swells and buckles. in a perfect world situation the framing will never get wet but unfortunately that sorta thing doesnt happern.. new homes get rained and snowed on during the courese of construction 

gbr's link is directly from a national site which states building codes.. yours im not so sure of.. regional codes do change though.. regarding habitat for humanitys practices they try to do things to the best of their ability however they are limited by the skill of the volunteers plus the more often than not the local building authorities are very very easy on them when it comes to inspection time do to the nature of the organization, i am very well aware of them as i am a build leader for the local h4h, ive come on site after being away for a few days to see things done which passed inspection which never would in a real inspection


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## HartKyle83 (Apr 22, 2012)

I cant imagine any inspector requiring an 1/8 gap all the way around. You would have to adjust your layout quite a lot to make this work as well as transfer the 1/8 gap to the drywall installation. You would have to run your drywall the same direction as the plywood. There are benefits standing the osb up but that is not how you want to install the drywall.


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## jklingel (Dec 21, 2008)

HartKyle83 said:


> There are benefits standing the osb up but that is not how you want to install the drywall.


 Hart: I have heard this: Residential, stand drywall up. Commercial, lay it horizontally. What is there to gain by having it horizontal? To me, that just ensures that you will have an unsupported joint to deal w/. (or do you automatically put blocking there anyway?) Then, too, what do you do w/ 9.5' high walls if you lay the drywall horizontally? Thanks.


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## Gary in WA (Mar 11, 2009)

I too, have seen framers have to cut gaps in roof sheathing after inspections. That link was from OSB of Canada. 
OSB is sized with a gap, no need to allow for it when laying-out framing. http://www.apawood.org/pablog/index.cfm/2006/5/15/Tips-for-avoiding-panel-buckling

Gary


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## Gary in WA (Mar 11, 2009)

Go here: http://www.gp.com/build/product.aspx?pid=5849

Scroll to the bottom of page, click on "Installation"

Choose to download; "APA guide- WALLS" (the first one)

Fig. #13- sheathing 1/8" gaps all around.

*Next to* fig. 20 (last one)- The ink stamps for "sheathing" all say "sized for spacing" on them.

Gary


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## Tom Struble (Dec 29, 2008)

ive also seen inspectors make guys go around each piece of sheathing with a saw

but i don't think the caulk negates or affects the purpose of the gap in any way 

but a carefully done wrb can be as effective regarding the 1/8'' gap imo


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## woodworkbykirk (Sep 25, 2011)

standing up osb when sheathing walls will fail inspection here anyway.. every sheet is clearly stamped with which way it should be installed.being horizontally.. every inspector knows to look for the arrows running perpindicular to the framing. 

standing up drywall is a commercial method, in residential is run horizontally.. so to reduce the number of joints and it makes for one joint at waist level for the taper to mud.. not 1000 vertical joints every 4'

as for adjusting the framing for the gap ??????????? every house ive ever framed we snap a chalkline 48 1/4" up from the bottom plate and install the sheathing to that.. the next row gets spaced by the thickness of a hand spike.. and so on.. when sheathing a roof both h clips and tongue and groove are made so to create the gap between the sheets

i seriously believe your overthinking this


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## jklingel (Dec 21, 2008)

Kirk: ah so. a 4' high seam is much easier to tape. i assume that requires blocking under it so you don't have a joint floating across 22.5"??? and what about a 9.5' ceiling? two horizontal joints? thanks.


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## cortell (Nov 27, 2010)

woodworkbykirk said:


> standing up osb when sheathing walls will fail inspection here anyway.. every sheet is clearly stamped with which way it should be installed.being horizontally.. every inspector knows to look for the arrows running perpindicular to the framing.


The advantage of installing OSB vertically is that every edge has a nailing surface. That significantly adds to the shear strength of the wall. Installing it horizontally requires installing solid blocking if you are to achieve the same shear strength (6" nail spacing on the edges). All that blocking bumps up material and labor costs. I don't think orientation alone affects the design strength of the wall. Now, roofs are a different matter...

That said...what works for one local building jurisdiction may not work for another.


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## Joe Carola (Apr 14, 2006)

cortell said:


> That said...what works for one local building jurisdiction may not work for another.


True , no blocking at all where I'm from installing sheathing horizontally.


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## jklingel (Dec 21, 2008)

you sure don't have the amount of nails in a sheet if you install structural sheathing horizontally. how that affects racking resistance i don't know. maybe two sheets nailed to the same stud (vertical installation) are a weak link. i'll have to ask the engineer about this when we chat later.


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## Gary in WA (Mar 11, 2009)

Fourth time in last two years; http://www.apawood.org/pablog/index...Sheathing-be-Installed-Horizontal-or-Vertical

Gary


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## Gary in WA (Mar 11, 2009)

After further research; the gaps are mainly for the acclimation from factory 6%-8%MC to outside application of 30-80%MC. After 48 hours, OSB has swelled to maximum---- *unless* wet later due to diffusion/water leakage. They even suggest nailing it on wall to support it, then later finish the nailing after it acclimates because it is an engineered product. http://www.apawood.org/level_c.cfm?content=pub_tch_libmain

Just be careful not to excessively over-drive the fasteners for reduced shear value; http://timber.ce.wsu.edu/Resources/papers/P81.pdf

Joe, NJ is not in a critical seismic zone as I am in "D"; http://publicecodes.citation.com/icod/irc/2009/icod_irc_2009_3_sec001_par004.htm

Kirk, Canadians must install their product horizontally for strength: http://osbguide.tecotested.com/pdfs/en/tb104.pdf

Gary


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## cortell (Nov 27, 2010)

GBR in WA said:


> Kirk, Canadians must install their product horizontally for strength: http://osbguide.tecotested.com/pdfs/en/tb104.pdf


Huh. Doesn't that contradict something stated in your previous link? Maybe there's something subtle in the language I'm missing...

_"The racking resistance of APA plywood or OSB wall bracing panels and the lateral load capacity of a shear wall for wind and seismic loading are not affected by the orientation of the sheathing panels. Panels may be installed with the long, or strength, axis either horizontal or vertical"
_


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## woodworkbykirk (Sep 25, 2011)

regarding blocking the edges of sheathing. the only time we have to install blocking is for a shear wall, that means a wall that is over 12' high and has to be sheathed to gain optimal strength

regarding drywall.. if your going to be framing walls 24" on center i hope to god your going to be using 5/8 board.. 1/2" isnt strong enough for that kind of layout, going over steel stud especially.. the only builders i know that are spec'ing 24" o.c locally are the cheap ass builders who have all kinds of issues with their houses and buildings a year after completion.


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## jklingel (Dec 21, 2008)

Gary: Doesn't the gaps/no gaps dilemma apply only to OSB, and not to plywood? I read the link and it clearly included plywood, but do people actually worry about gaps w/ plywood in the real world? This is another reason to avoid OSB, I think.


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## HartKyle83 (Apr 22, 2012)

cortell said:


> The advantage of installing OSB vertically is that every edge has a nailing surface. That significantly adds to the shear strength of the wall. Installing it horizontally requires installing solid blocking if you are to achieve the same shear strength (6" nail spacing on the edges). All that blocking bumps up material and labor costs. I don't think orientation alone affects the design strength of the wall. Now, roofs are a different matter...
> 
> That said...what works for one local building jurisdiction may not work for another.


The blocking and the gap are the reasons I stand it up but my understanding is that it is stronger ran horizontally. This is why I like to hang my drywall vertically. It is easier to tape it horizontally with no but joins but the walls benefit from the horizontal application.


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## HartKyle83 (Apr 22, 2012)

woodworkbykirk said:


> standing up osb when sheathing walls will fail inspection here anyway.. every sheet is clearly stamped with which way it should be installed.being horizontally.. every inspector knows to look for the arrows running perpindicular to the framing.
> 
> standing up drywall is a commercial method, in residential is run horizontally.. so to reduce the number of joints and it makes for one joint at waist level for the taper to mud.. not 1000 vertical joints every 4'
> 
> ...



That gaps the plywood on two sides. What do you do about the other two sides? That is when I brought up layout. 1/8 at a time will add up to a lot in the course of a long wall. But then I see all this talk about sized for spacing so I am going to go check out a piece of osb and see whats up.


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## HartKyle83 (Apr 22, 2012)

GBR, I was hoping you would comment on hot you are talking about conditioned and unconditioned space.


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## ratherbefishing (Jan 13, 2011)

Wow! This thread is a year old. And I started it!


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## jklingel (Dec 21, 2008)

Rather: Well, is the job done yet? 
Kirk: Plenty of good builders have walls 24" OC because of the better thermal performance and aligning studs right under trusses, eliminating the need for a double top plate. At least one I know who uses 24" OC puts his plywood on the exterior of the inner 2x4 (double stud wall), which is his air barrier. I suspect that helps stabilize the studs, but I think he still uses 5/8" drywall. Yes, 5/8" drywall is certainly best w/ 24" OC, though I know one who uses 1/2" w/ no issues in 20 some years. One thing I thought of whilst out at the range: if you install drywall horizontally, that kills the option of using the airtight drywall approach, unless you block at the edges.


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## Tom Struble (Dec 29, 2008)

ratherbefishing said:


> Wow! This thread is a year old. And I started it!


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## ratherbefishing (Jan 13, 2011)

JK,
I hate to admit, it's going slow. Outside's done, roofed, painted. Electical and plumbing inspections are done. Kerdi's done, shower's tiled, not grouted. No time for the next few weeks. Lucky it's a second bath!


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## jklingel (Dec 21, 2008)

ratherbefishing said:


> Lucky it's a second bath!


 At least lucky for co-workers.


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## HartKyle83 (Apr 22, 2012)

jklingel said:


> Rather: Well, is the job done yet?
> Kirk: Plenty of good builders have walls 24" OC because of the better thermal performance and aligning studs right under trusses, eliminating the need for a double top plate. At least one I know who uses 24" OC puts his plywood on the exterior of the inner 2x4 (double stud wall), which is his air barrier. I suspect that helps stabilize the studs, but I think he still uses 5/8" drywall. Yes, 5/8" drywall is certainly best w/ 24" OC, though I know one who uses 1/2" w/ no issues in 20 some years. One thing I thought of whilst out at the range: if you install drywall horizontally, that kills the option of using the airtight drywall approach, unless you block at the edges.


once you tape it the many pieces of a wall become one making the air tight approach attainable with no extra blocking


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## cortell (Nov 27, 2010)

jklingel said:


> One thing I thought of whilst out at the range: if you install drywall horizontally, that kills the option of using the airtight drywall approach, unless you block at the edges.


Similarly, the claim that drywall installed horizontally improves the shear strength of the wall seems dubious to me. Fastener spacing is a significant factor. Doesn't reducing the spacing from 6"OC to 16"OC (if not 24"OC!) along the horizontal middle seam sound like a win-lose situation? Sure, the drywall spans more joists, and the end joints are staggered, and the strength axis is supposedly along long the length of the panel...but has anyone figured out what the net gain in shear strength is after taking into account the loss caused by a reduced nailing schedule?

I know there are other benefits to horizontal drywall, and I'm not trying to stir up that bees nest. Just curious about this shear strength claim.


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## woodworkbykirk (Sep 25, 2011)

klingle, im very aware of the method. ive built several of them and their horrible for high wind zones.. not to mention getting up on the roof, you can feel the place swaying. i built one 5 years ago, during construction a hurrican hit.. one wall racked out of plumb by 3/4". another local builder had one in construction that was to be their showcase home for the year, during framing a hurricane hit and it racked by 2 1/2" they tried to push it back into alignment with a machine but didnt work.. had to be torn down and start new

when it comes to finishing these places. their even worse.. blocking is always missed, your relying on glue to hold trim in place and even custom built closets are held on with glue


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## jklingel (Dec 21, 2008)

kirk; got it. i am debating the OC for my new house. one option i dreamed up (and i am sure 1,000 other people have already done, and maybe abandoned) is using double 2x4's, 24" OC. that gives me a 1.5" nailing surface for the plywood and drywall. for loads, i can not use a single 2x4, 24" OC, so I'll either have to go 16" or 12" OC with singles. another option is to fabricate T's out of 2x4's. i think they will carry the load adequately if 24" OC, but obviously will require a lot of extra (non-paid; my wife refuses to pay me) work. dunno yet. just tinkering w/ ideas. on the airtight drywall approach w/ horizontal drywall (whoever mentioned that), i don't think the spans would be as tight as if the edges were on studs and gooed, as you'd do if vertically installed. dunno; will have to look into that more.


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## Gary in WA (Mar 11, 2009)

Loose ends; I would tape the OSB/ply rather than foam/caulk when un-backed for an air barrier. I would use the drywall for the air barrier, caulking at the stud/*sheathing*/plates to minimize air movement. I would use cellulose to help stop convective loops/airflow. I would never caulk/glue the expansion gap suggested left open by all manufacturers between OSB, all sides. I would use a "stucco" housewrap against OSB because it dries so slowly. Especially between OSB/foam board.

Drywall is about 3X stronger going with the grain (long way) than across, both in "flex. strength" and "MOR"; https://docs.google.com/viewer?a=v&..._w2ARf&sig=AHIEtbT3-jS_UFfs-iaiU1o3kfoOlKl-7Q

Gary


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## jklingel (Dec 21, 2008)

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. ???


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## HartKyle83 (Apr 22, 2012)

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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## woodworkbykirk (Sep 25, 2011)

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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## HartKyle83 (Apr 22, 2012)

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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## jklingel (Dec 21, 2008)

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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## Gary in WA (Mar 11, 2009)

jklingel said:


> 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/documents/insights/bsi-038-mind-the-gap-eh/?searchterm=foam%20board%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.aspx?repository=bp&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/handle/1969.1/4625/ESL-HH-04-05-25.pdf?sequence=4


Gary


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## jklingel (Dec 21, 2008)

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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