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George Walker 01-12-2011 08:12 PM

taping OSB sheathing joints
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>

jlmran 01-12-2011 08:15 PM

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

George Walker 01-12-2011 08:22 PM

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).

jlmran 01-12-2011 08:29 PM

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

jlmran 01-12-2011 08:32 PM

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.

jlmran 01-12-2011 08:37 PM

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

loneframer 01-12-2011 08:39 PM

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.

loneframer 01-12-2011 08:46 PM

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

Roofmaster417 01-12-2011 08:52 PM

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.

Gary in WA 01-12-2011 09:01 PM

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;

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;

Seattle, in WA State has 36” annual rainfall and they won’t use it;

Building Science explains it well, and don't use SPF with OSB;

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;

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;


Roofmaster417 01-12-2011 09:16 PM

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

Tom Struble 01-12-2011 09:54 PM

: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

Gary in WA 01-15-2011 05:34 PM

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;

Tom Struble 01-15-2011 05:41 PM

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

Gary in WA 01-15-2011 06:24 PM

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;


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