# taping OSB sheathing joints



## George Walker (Jan 13, 2011)

I've sheathed my house with OSB, and intend to use Typar house wrap. I was trying to foind out what type of tape would work best and got lots of flack about taping it. I think the abatement of air infiltration is necessary, typar folks said it would imped the house from breathing properly, I say bunk. I have 2x6 studs and intend to use unfaced fiberglass bats, lots of expanded foam sealant and a 4 mil vapor barrier, any cogent comments? especially taping OSB joints>


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## jlmran (Feb 8, 2010)

What will the tape do which Typar won't do?


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## George Walker (Jan 13, 2011)

*osb joint taping*

You got me i was flaberghasted when they said taping the joints would impede breathability. I thourht air infiltration was the big villan, followed by trapping water vapor and then mold. I don;t see any down side in taping these joints ( except time and money).


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## jlmran (Feb 8, 2010)

My point was...Typar acts as an air barrier, so why tape?


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## jlmran (Feb 8, 2010)

From Typar's website:

The TYPAR® Weather Protection System provides superior air and water holdout, exceptional moisture vapor transmission, superior tear strength and optimal surfactant resistance PLUS The TYPAR Advantage. At the heart of the system is TYPAR® HouseWrap which acts as an air and moisture barrier, while simultaneously allowing moisture vapor to escape from the wall cavity to the outside. Installed before the exterior siding, TYPAR HouseWrap protects your home from Nature’s harshest elements and has exceptional tear strength and ultraviolet stability. It also provides energy-efficiency for years to come which is important for energy and budget conscious consumers.


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## jlmran (Feb 8, 2010)

You're free to tape if you want. Would Advantech's Zip tape adhere to OSB?


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## loneframer (Mar 27, 2009)

Personally, I would not tape the joints, for several reasons.

First, I don't know of a tape that would hold, long term.

Second, I agree that sealing the seams would impede breathability of the wall cavity, especially with OSB. OSB has a lower PERM rating than plywood, decreasing its ability to move water vapor to the outside, where it can dissipate.

Housewraps have many different make-ups, which can alter the overall permeability of the building envelope, as well.

Moisture needs to dry to one side of the wall or the other. If the VB is inside, the exterior wall must be permeable. Taping the seams will lower the overall PERM number, making moisture issues more likely.

In addition, I prefer asphalt saturated felt as my WRB, due to its variable permeability. The more moisture in the wall cavity, the more permeable it becomes. As drying occurs, it becomes less permeable, allowing better water hold out.

Insulation is great, but ventilation is necessary. Finding the right balance is science.


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## loneframer (Mar 27, 2009)

As a note, I also space all my sheathing to manufacturers specifications.


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## Roofmaster417 (Jun 9, 2010)

What state are you in ? Some think that taping the seams is pointless but in some areas its mandatory. This "taping" is common in areas that have high velocity winds. Miami/Dade county its a requirement I know for sure. Other states that are prone for high velocity winds are any state that are coastal, mainly the gulf coasts.(hurricane areas)It is your money so spend it as you like but I feel its pointless otherwise.As far as the ("taping) limiting air flow or breath ability that is incorrect. Proper ventilation will eliminate any breath ability concerns.(attic vents, pan vents,ridge vents,turbines,attic power vents,smart vents,gable vents,and soffit) The only issue I find questionable with taping the seems is buckling of the O.S.B/CDX, since your home is constantly shifting.


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## Gary in WA (Mar 11, 2009)

The vapor barrier is probably not required in the U.S., where are you located?

The fiberglass comes with or without convective loops, your choice; http://www.diychatroom.com/f98/how-buy-choose-fiberglass-insulation-90438/

The OSB needs to breath. You want to stop the moisture coming from the house with a vapor retarder, possibly just paint on the drywall, again, your location? 

OSB is worse than plywood for drying out or letting moisture through from the inside room, it takes so long, 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

Seattle, in WA State has 36” annual rainfall and they won’t use it; http://www.google.com/url?sa=t&sour...sg=AFQjCNFJ2MdFsnNbhi5K0LFgRmKEJSz4eA&cad=rja

Building Science explains it well, and don't use SPF with OSB; http://www.buildingscience.com/docu...nd-the-gap-eh/?searchterm=foam board in walls

Typar (11.7 perms) will prolong the drying of OSB from *12 days* (Tyvek 58 perms.) to* 40 days *encouraging mold, page 15, Fig. 15; http://repository.tamu.edu/bitstream/handle/1969.1/4625/ESL-HH-04-05-25.pdf?sequence=4

If you need an air barrier, that is what house wrap is for; “The approach used to install an appropriate weather-resistive barrier is dependent on why it is being used. If intended only to
resist water entry, a weather-resistive barrier must be properly lapped and integrated with other flashing—taping of all seams is not critical. *If it is used to reduce air infiltration, all seams and*
*edges must be sealed with compatible tape or sealant*.” From; http://apps1.eere.energy.gov/buildings/publications/pdfs/building_america/28600.pdf


Gary


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## Roofmaster417 (Jun 9, 2010)

I guess I am a "lully headed nenny mugging" Are you talking about a roof or siding?


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## Tom Struble (Dec 29, 2008)

:laughing:i think he's talkin sidewall

the whole problem i have is how do we know whether spacing the sheathing actually does anything for this drying out to happen?

i could see it happening when individual t&g boards and little or no insulation were being used but i'm a little skeptical when sheet goods are used that this spacing promotes drying


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## Gary in WA (Mar 11, 2009)

Good point, Tom. I would guess that OSB dries out from 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 it dries out, shrinking, leaving gaps underneath for air to pass there. With a shop, no biggy, but a house, with the 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" times 16'+- edge seams for an extra area to dry;


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## Tom Struble (Dec 29, 2008)

good points Gary:wink: assuming taping the seams dosen't keep out more moisture from the wall cavity,than not taping lets out...i barely understood what i just typed:huh:


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## Gary in WA (Mar 11, 2009)

I left off a site that had spray on permeable material that is an air barrier, but lost it in my library..... I sent the post without that or my name, which is a second time now..... I need a nap.....

I think you’ll find this interesting on air barrier joints; http://www.tallwallosb.com/features-and-benefits 

Gary


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## MJW (Feb 7, 2006)

We are "air sealing" all our walls here in MN. Not a good idea IMO. Good for energy, bad for mold/moisture. Which one will affect you sooner?

No horizontal gaps like mentioned in the link. Our sheathing is put on vertically and the seams on taller walls are simply blocked with 2x's.


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## Tom Struble (Dec 29, 2008)

i'm going to start drillin vent hole pores in the walls from now on:smartass:


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## loneframer (Mar 27, 2009)

Soooo, you guys think sealing up the gaps on the sheathing is a good thing?

Isn't that moving one step closer to an exterior vapor barrier?

In my climate zone, I've been taught that the exterior wall surface needs to be several times more permeable than the interior. 

Creating a non-permeable surface on both sides of the wall assembly sounds like cetain failure to me, considering the virtual impossibility of closing up all the gaps between framing and finish materials attached to the wall.

Moisture will find a way in, giving it a little help getting back out is a good thing, IMO.

If you want an airtight wall assembly, you may as well just tar and feather it, allowing it to be the albatross that it is.


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## loneframer (Mar 27, 2009)

tomstruble said:


> i'm going to start drillin vent hole pores in the walls from now on:smartass:


Hmmm, perforated wall sheathing......

It's a shame that ideas already been taken by the ridgid foam guys.


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## Gary in WA (Mar 11, 2009)

In 1988, when I converted my 2 attic rooms to 3 bdrm. and a 3/4 bath, I cut slots in the OSB every 6" apart because I had installed it on new houses and knew it repelled water and of the advertised perms when it first came out here, years earlier. Don't do this if required on the corners or for a structural (shear) wall. No mold yet as I replaced some siding this year from raccoon damage, though the 15# felt paper was thin and brittle. (use 30#, especially today.......) Tom, Dupont Tyvek is one of the spray-on, air barrier but moisture permeable; http://docs.google.com/viewer?a=v&q=cache:uawmJu69hb0J:www2.dupont.com/Tyvek_Weatherization/en_US/assets/downloads/pdfs/072619%2520-%2520Dupont%2520Tyvek%2520Fluid-Applied%2520Weather%2520Barrier%25208%2520Apr10%2520FINAL%2520(2).doc+test+of+air+leakage+at+sheathing+joints&hl=en&gl=us&pid=bl&srcid=ADGEESjlBfOXaN67ZGT7b6MnI1csjEoovZyTBxmqUVawL27OnbWrZRsBP8HGxSDMvIJKuCT9EwO0QoZEZ3QAwQTlqpvaoyxN6UdiJc6uokDDCEml7-utVElaQL-3HuflzCpNvS8Icw3i&sig=AHIEtbR2MyFSlEMDVUtt8eiQhngFLZ5U6Q

Gary


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## Tom Struble (Dec 29, 2008)

loneframer said:


> Sooo, you guys think sealing up the gaps on the sheathing is a good thing?
> 
> Isn't that moving one step closer to an exterior vapor barrier?
> 
> ...


 
i don't think taping the osb seams is a good idea,or even effective over the long term,and combining that with a foam wrb,well...i for one have my doubts

i know Gary keeps telling me how much less permeable osb is compared to ply,it's just that in my experience ive never personally seen a big difference [from a moisture management point] between the 2

just like i never saw a difference between plastic or felt wrbs,i read the science but i don't see the difference in my ''real'' world


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## loneframer (Mar 27, 2009)

tomstruble said:


> i don't think taping the osb seams is a good idea,or even effective over the long term,and combining that with a foam wrb,well...i for one have my doubts
> 
> i know Gary keeps telling me how much less permeable osb is compared to ply,it's just that in my experience ive never personally seen a big difference [from a moisture management point] between the 2
> 
> just like i never saw a difference between plastic or felt wrbs,i read the science but i don't see the difference in my ''real'' world


 Well Tom, real world conditions are what I base my opinions on as well.
I believe my own two eyes before I believe what I read. However, when I read something that reinforces what I have seen with my own eyes, it carries more weight.


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## Tom Struble (Dec 29, 2008)

i wasn't tryin to be persnickety:no:

http://dictionary.reference.com/browse/persnickety

i know you have seen tyvek become brittle,so have i:yes:but only the early version


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## loneframer (Mar 27, 2009)

tomstruble said:


> i wasn't tryin to be persnickety:no:
> 
> http://dictionary.reference.com/browse/persnickety
> 
> i know you have seen tyvek become brittle,so have i:yes:but only the early version


 I wasn't sniping at you Tom. I still bow to the vinyl king.

I was speaking in broader terms than that, but since you brought it up, yes I prefer asphalt saturated felt for a WRB, in almost every scenario.

All together now..."*Variable Permeability*":thumbup:


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## Tom Struble (Dec 29, 2008)

:laughing: i know i know i know i know........your the best:thumbup:


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## jmiller (Nov 19, 2010)

OSB has variable permeability as well. Once it turns to mush it is totally permeable.


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## Tom Struble (Dec 29, 2008)

:laughing:


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## Gary in WA (Mar 11, 2009)

Figures 27, 46, 57, 77, etc.,........ http://www.google.com/url?sa=t&sour...sg=AFQjCNGB8MUiRVLx8S3CG5MQqPAgDCcvwQ&cad=rja

Gary


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## loneframer (Mar 27, 2009)

jmiller said:


> OSB has variable permeability as well. Once it turns to mush it is totally permeable.





tomstruble said:


> :laughing:


 Oh, I see how it's gonna be around here.:wink:


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## jmiller (Nov 19, 2010)

loneframer said:


> Oh, I see how it's gonna be around here.:wink:


Yup, Tom and I try to act like we know what we're talking about :jester:


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## loneframer (Mar 27, 2009)

GBR in WA said:


> Figures 27, 46, 57, 77, etc.,........ http://www.google.com/url?sa=t&sour...sg=AFQjCNGB8MUiRVLx8S3CG5MQqPAgDCcvwQ&cad=rja
> 
> Gary


 Interesting story.

I don't think taping the OSB seams would have changed the outcome though.

The truth is, I don't believe that OSB, joint taping, or felt paper are the guilty parties.

A stucco application such as that requires 2 layers of felt, or any other WRB, IMO.

The stucco will bond to the outer layer of WRB, eliminating it's ability to drain. The stucco gets wet, stays damp and the moisture will be driven through the WRB in the wrong direction. The inner layer will act as the rain screen and allow moisture to drain away
. There were so many installation infractions in that homes exterior that I'm not aware of any structural sheathing product that would not have failed.

I will say that all the cracking in the stucco was probably due to swelling of the OSB, but you can't blame the OSB for that homes problems.:no:


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## loneframer (Mar 27, 2009)

jmiller said:


> Yup, Tom and I try to act like we know what we're talking about :jester:


 Yeah, you guys are OSB haters, but moisture is the route to all problems OSB.

Suppose you have a leaky pipe. All your furniture and personal belongings get ruined. Do you file a claim for water damage or pipe damage?

Water is the guilty party. Even if installation of the pipe was the real cause of the failure. Control the water, control the damage.


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## jmiller (Nov 19, 2010)

I don't hate OSB at all. We use it on roof decks all the time.

I hate poor flashing details.


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## Tom Struble (Dec 29, 2008)

i no hate osb either....Gary on the otherhand:whistling2:


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## Shamus (Apr 27, 2008)

Really good stuff guys.

Older homes had more sq inches of holes than you could shake a stick at. Expensive to heat/cool but typically dry from the draft. 

New construction closed the envelope. Add a temperature difference on the other side of the wall and you have a problem unless you design for it to vent (dry out). 

I'm sure there are some builders out there that address this from the foundation to the attic, but I only see the horror stories.

OSB, :thumbsup: great for roofing and garages.


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## Gary in WA (Mar 11, 2009)

Lol, those pictures were in response to it turning to mush from the previous post. I dislike OSB on walls only, because it acts as a vapor barrier due to low permeability and waxed face, trapping moisture coming from the house. True, water control, outside and inside, is the key.
Tom, did you read my "biggest loser"? http://www.diychatroom.com/f98/how-buy-choose-fiberglass-insulation-90438/

I'm 1/2 done with one on OSB...... 

Gary


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## Tom Struble (Dec 29, 2008)

i did now:thumbsup:


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## jmiller (Nov 19, 2010)

GBR in WA said:


> Figures 27, 46, 57, 77, etc.,........
> Gary


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## P_Vilefort (Sep 5, 2021)

George Walker said:


> I've sheathed my house with OSB, and intend to use Typar house wrap. I was trying to find out what type of tape would work best and got lots of flack about taping it. I think the abatement of air infiltration is necessary,Typar folks said it would impede the house from breathing properly, I say bunk. I have 2x6 studs and intend to use unfaced fiberglass bats, lots of expanded foam sealant and a 4 mil vapor barrier, any cogent comments? especially taping OSB joints.


Contrary to popular belief, vented attics cause a significant waste of heating and cooling energy as well as $$. A tight house reduces energy usage. You would have to seal all penetrations through the sheathing including nail heads to ensure no leaks. If you follow thebildshow, there are houses shown in a number of videos that have only exterior insulation and the roof joists were cut off at the edge of the walls to make a completely tight envelope. The roof substructure was added after the roof sheathing was covered with two layers of polyiso foam and then an additional layer of Zip OSB and the seams were taped. Look for thebuildshow on YouTube to see the house. What will be done to ensure there is adequate air exchange is the installation of an ERV; an air-to-air heat or cooling exchanger. It takes outside air and extracts heat or cool from the air leaving the house in order to have a fresher air exchange. This also gets rid of excessive interior moisture. If you seal the living space properly, the vented attic will do nothing for you. However if you seal the entire house including the attic, you can prevent excess inflows and excessive outflows. The ERV lets you control the air exchange instead of relying on the leaks to give air exchange. The ERV also gives you much cleaner air from an outside source.
Rockwool will give you much more insulation value than fiberglass. The Rockwool material is flame resistant (will not support combustion) and water resistant (will not absorb water).


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## P_Vilefort (Sep 5, 2021)

loneframer said:


> Soooo, you guys think sealing up the gaps on the sheathing is a good thing?
> 
> Isn't that moving one step closer to an exterior vapor barrier?
> 
> ...


Exterior grade plywood and OSB are not impermeable materials. Taping the seams prevents air leakage while still allowing the materials to expand and contract. If you are planing to use exterior polyiso or similar insulation board you would install 3/4 inch furring strips to the sheathing before applying the insulation board. The furring strips should line up with the framing timbers. At the top and the bottom of the wall you install what looks like plastic corrugated cardboard cut from a sheet that is the same thickness as the furring strips. This allows air to get into and out of the space, because it is not going to go through the polyiso board. There are other exterior insulation boards that are very moisture permeable. I think Rockwool makes one type. Then if you want to you can wrap away. If you plan on using something like Hardie siding with the polyiso insulation board you will need to add furring strips to the insulation board to allow any moisture accumulation behind the siding to get out the bottom. Here you would use the corrugated plastic again to allow moisture movement. You can also add a small pore screen to keep out any bugs, like mud dabbers (small wasps). The siding is nailed to the furring strips. This is shown in lots of details on TheBuildShow.
If you are building new you have to instruct the plumbers, electricians, etc. that they can only make one hole to put in one wire or one pipe, etc. No large holes for multiple items. Think about all of the little bugs that can get through larger holes. Why spend the money to build a house when you just let the outside in to live with you. If that is good enough then live in a series of tents.
If you are building new or fixing an older house that was never built correctly, then use about 2 to 2.5 inches of exterior insulation to give an R14 and then add insulation between the studs to give you another R14 to R15. The wall will now approach or exceed R30. I live in a 40 year old house that has almost no insulation anywhere in it and almost no sheathing on the outside except for the roof decking. I don't know how they got away without putting on sheathing when it was a code requirement. The home inspector missed the lack of sheathing.


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## P_Vilefort (Sep 5, 2021)

I forgot to add that if you are using a non-permeable insulation board on the outside you should tape all the joints too, to prevent air penetration.


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## ront02769 (Nov 28, 2008)

where I am currently working we are required to tape all exterior osb/plywood seams. then covered by a house wrap which also has to have all seams taped. Pain in the butt.


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## P_Vilefort (Sep 5, 2021)

When I originally wrote about taping the OSB I was thinking about the OSB used for roof decking. In the event high wind took off part of the finished roofing the taped seams would prevent water intrusion. When the sheathing is exposed and there are open seams or joints the water will pour into the attic and then down into the house. You wouldn't believe the amount of water that will come through a 3/16 or 1/8 inch gap. If the tape stays put and is under the water proof barrier, the likelihood of water intrusion is less even if the waterproof barrier is partly removed. Some of the tapes can be exposed to the elements for up to 60 days without creating future problems.


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## Nealtw (Jun 22, 2017)

They had the guys taping joints on the walls here for about a month and then changed their minds and the idea was dropped.


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## P_Vilefort (Sep 5, 2021)

ront02769 said:


> where I am currently working we are required to tape all exterior osb/plywood seams. then covered by a house wrap which also has to have all seams taped. Pain in the butt.


There are some new materials that take the place of the house wrap and are sprayed onto the exterior surfaces after the joints are taped. I saw it on Instagram. It was used on college/university dormitories..


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