This is probably a stupid question; but...

All of the information I've found on here about air sealing the exterior-sheathing side of the stud bays talks about going around after the walls are up and sealing between the OSB and the king/jack studs and top/bottom plates.  I intend to air seal with acoustic sealant per information on this forum... but is there any reason I couldn't just run a fat bead along the outside of the studs before putting each piece of OSB on?  I'll be doing my own framing and the OSB will be installed before the walls are raised.  Seems like it'd be a lot faster than doing it after the sheathing is on because there's just one bead on each stud instead of two (one for each "bay").  This would be that much easier in my case because of the 15' ceiling height... much faster, easier, and safer to run a bead on the studs while they're flat on the ground than going up/down a ladder to do each bay afterward.  At least get 80%+ of the sealing done in that manner and finish up the rest once the walls are in place.  I can't come up with any reason why this wouldn't work; but felt compelled to ask since I've not seen it done in this manner with the examples I've found.  Thanks!

Consider using gaskets instead of caulk. I suspect that they work better over many years although I haven't seen data either way. Or just use tape and possibly an air barrier film.

thats a great idea and you should go for it. Use a great sealant, not some inexpensive "painters caulk" as you want it to last for decades. It won't be all you'll need to do since there are lots of horizontal joints in the sheathing that need to be sealed. that approach plus a first class tape on the exterior like ZIP sheathing and tape or SIGA tape on OSB should do the trick.

EDPM gaskets are also a necessity in building a great house. they should always be used between the concrete and the PT plate. We also use them on exterior wall plates. Conservation Technology sells good ones online, but I'd like to see them at HD and every lumber yard. The thin colored foam stuff is put down by most people to make you think it accomplishes something; it doesn't.

The cheap foamy gaskets accomplish something- perhaps not as much as we'd like it to do, but it's way better than nothing, at least from a capillary draw point of view.

+1 on the use of EPDM as the preferred material between concrete & wood.

The problem with caulk is that a gap might be approximately zero when assembled and then increase to 1/8" as moisture levels change. I don't know of any caulk or glue can expand over that range. Many don't expand at all after they are applied and cured. But a gasket can adapt from 1/16" when installed to 3/16" months later.

"The cheap foamy gaskets accomplish something"
Dow Chemical agrees with you - their ads say"It provides excellent and enduring resistance to water and water vapor." I agree - plastic is unaffected by water; this is not news. But it is used primarily by builders to "help reduce air infiltration" and in that it is a dismal failure. The issue from this builder's perspective is not to encourage people to eliminate the "cheapy foam" in favor of a direct wood to concrete joint, but instead to use something that really works for it's intended and primary purpose, which is to cut down on air infiltration. EDPM gaskets cost less than $1 per foot, so on a 30x40 colonial that would be less than $150 - for a product that could save that much fuel in no time compared to the cheapy foam. From a long term building performance perspective it is a very inferior and ineffective product and should not be used. Period.

Am I on the right track here?:

http://www.conservationtechnology.com/building_gaskets.html

I assume the "drywall gaskets" are what I should use between the OSB and studs.

the building gaskets are for the plates; drywall gaskets for the drywall (attach to edges of top plates). They would also work on the studs, but I prefer taping the plywood joints - cheaper & faster

Posted By Bob I on 11 Jul 2013 01:11 PM 
I prefer taping the plywood joints - cheaper & faster

So it is not necessary to use accoustic sealant around the perimeter of the stud bays if the OSB seams are taped?  Most of the information I've found on air-sealing (even on this website) recommends sealing around the perimeter of each stud bay where the exterior sheathing meets the studs... highlighting either the "professional" products for those who want it done, or using a high quality accoustic sealant for [cheap] people like me who want to do it themselves.

As far as the SIGA tape mentioned above, do you have a link to a specific product you recommend?  A search for SIGA tape yeilded a lot of non-building-related products.  This product appears to meet the specs you're talking about; but the website is for a different country and minimum order is 100 rolls:

http://www.siga.ch/en/product-overview/wigluv-60-detail.html?&frage=565

I remember seeing some kind of fiber-reinforced sealant they were using on the exterior sheathing joints of a passive house video I was watching on youtube several months ago.  Any comments on that over the tape? 

Thanks to everyone for the information... about the time I think I know enough to move forward, something new comes to light.

Note that in some cases you will need to use a primer for OSB. Also look at 3M All Weather Flashing Tape 8067.

studs dry out, shrink and twist over time so caulk joints can crack. the important joints to seal from the inside in my opinion are the top and bottom of the bays, but taping the exterior has worked very well on the homes I've built, with ACH (infiltration) numbers near passive house levels (we would have below except that the two flue chimney and wood burning fireplace added to the complexity; still, it was .78 ACH50). I have not used the spray coatings but I would guess they probably work very well.

there are SIGA distributors on both coasts anyway; I buy from maine green building. the exterior tape is Wigluv the 60mm is 2-1/2" and is an amazing product - Acrylic non toxic adhesive so it can be used on damp surfaces. Sticks to most everything, concrete needs a special primer. It is $52/82' roll, and well worth the cost. We typically use ZIP sheathing with the ZIP tape. One of my subs runs a "shoe" test - to patch his work boots and had excellent results with this.

http://www.mainegreenbuilding.com/products/building-materials/moisture-barriers/siga-air-windtightness-system/
http://www.mainegreenbuilding.com/wp-content/uploads/2012/07/SIGA-Wigluv-KM6682.pdf

Okay, so here's my recap:

1. EDPM gasket between bottom sill and concrete
2. SIGA tape all exterior OSB joints
3. Acoustic sealant at top and bottom joint of each bay (will probably do this along the side of the bays that are against an outside corner as well).  
4. Accoustic sealant between 1st and 2nd plate of the double top plate?  Maybe put a little on the lower plate before putting on and face nailing the upper plate, then also run a bead along the seam once they're fastened together.

Anything I'm missing?

Unless you are addressing a noise issue, I'd skip the acoustic sealant and replace it with tape.

For the top/bottom of the bays, seam of the double top plates, or both?

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