# Question about sealing top plate



## Tally Wacher (Nov 17, 2015)

I've just begun installing accuvent soffit baffels and sealing the exterior wall top plate prior to blowing cellulose. My question is do I really need to seal the top plate? Haven't the drywall joints been sealed with joint compound from the inside? It is a bit*h getting to the top plate due to the pitch of the roof and it is difficult to position the foam gun with can attached in such tight quarters. Thanks.


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## SeniorSitizen (Sep 10, 2012)

I'd bet my life savings the dry wall was not sealed to the top plate during construction.


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## Tally Wacher (Nov 17, 2015)

In many sections, I can see dried joint compound that has oozed into the attic space


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## joecaption (Nov 30, 2011)

Got some pictures?
Not even sure why you would be using a foam gun there.
I've never seen a top plate being sealed.


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## Fix'n it (Mar 12, 2012)

joecaption said:


> I've never seen a top plate being sealed.



mine are. when i put the drywall up i caulked all of the studs as i was installing it. and i sealed the 1" xps as i installed that in the cavity.


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## Bud9051 (Nov 11, 2015)

Hi Tally, fun getting out there isn't it .
As Joe said, I also don't use the foam, I use caulking and can employ my fingers. That foam is messy enough without working in tight places.

As for importance, the electrical penetrations and the paper thin gap between the drywall and the top plate allow any air that enters the cavities to make its way into the attic. The Accuvent baffles that extend over the top plate and a bit into the soffit allow for more insulation over the top. Infrared pictures of most homes will always show those double plates as cold, just wood for insulation.

Unfortunately, the sheathing to top plate seam offers a similar leakage path the would have needed to be sealed when built. Do what you can, get the electrical holes, and add another inch of insulation to more than compensate.

Bud


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## Gary in WA (Mar 11, 2009)

I foresee more air sealing requirements that will be enforced. Other than bottom plates of exterior walls and attic knee walls, and others as we have now; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_11_sec002_par022.htm Did you notice "breaks or joints"? --- That is the drywall on the wood stud/plates *after *(meets code at install)the wood expands/contracts with the seasons. Why do we "float" the ceiling drywall at the corners- because the truss up-lifts, taking the drywall with it. Joint compound/tape does not stop moisture as well as the 1/2" thick 15 minute fire resistance barrier = board. 

The biggest problem with fibrous insulation in a cavity is air infiltration to degrade the R-value tremendously. So the drywall to plate has a gap after the studs acclimate and change with each season, and the corner paper/texture mud lets moisture through because it is not 1/2" thick (usually tapers cover the gap without pre filling it first- required by drywall manufacturers, on an exterior wall- coldest of walls. So the heated room wall cavities are supplying warm moist air to the attic to cause ice dams... put a plastic straw extension on the nozzle; automotive vacuum hose or plastic soda straw, or house water filter 1/4" tubing (3') with a stick handle (4'), get creative.

Gary


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## Tally Wacher (Nov 17, 2015)

joecaption said:


> Got some pictures?
> Not even sure why you would be using a foam gun there.
> I've never seen a top plate being sealed.


There are a lot of sites that say to seal the top plate. Here is a pic:








You can see the white joint compound between the drywall and stud.



Bud9051 said:


> Hi Tally, fun getting out there isn't it .
> As Joe said, I also don't use the foam, I use caulking and can employ my fingers. That foam is messy enough without working in tight places.
> 
> As for importance, the electrical penetrations and the paper thin gap between the drywall and the top plate allow any air that enters the cavities to make its way into the attic. The Accuvent baffles that extend over the top plate and a bit into the soffit allow for more insulation over the top. Infrared pictures of most homes will always show those double plates as cold, just wood for insulation.
> ...


I have a new respect for the guys that do this for a living. Repiping my house was a cake walk compared to this. 
As far as using a caulk gun, I am not able to reach the top plate with my finger. Therefore, I am not able to secure the top plate portion of the accuvent with staples as I can not reach.



Gary in WA said:


> I foresee more air sealing requirements that will be enforced. Other than bottom plates of exterior walls and attic knee walls, and others as we have now; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_11_sec002_par022.htm Did you notice "breaks or joints"? --- That is the drywall on the wood stud/plates *after *(meets code at install)the wood expands/contracts with the seasons. Why do we "float" the ceiling drywall at the corners- because the truss up-lifts, taking the drywall with it. Joint compound/tape does not stop moisture as well as the 1/2" thick 15 minute fire resistance barrier = board.
> 
> The biggest problem with fibrous insulation in a cavity is air infiltration to degrade the R-value tremendously. So the drywall to plate has a gap after the studs acclimate and change with each season, and the corner paper/texture mud lets moisture through because it is not 1/2" thick (usually tapers cover the gap without pre filling it first- required by drywall manufacturers, on an exterior wall- coldest of walls. So the heated room wall cavities are supplying warm moist air to the attic to cause ice dams... put a plastic straw extension on the nozzle; automotive vacuum hose or plastic soda straw, or house water filter 1/4" tubing (3') with a stick handle (4'), get creative.
> 
> Gary


I am using the pro 14 foam gun and pro size can of great stuff attached to a 3' section of 1/2" tubing which is in turn connected to a 4' piece of 1/2" pex tubing I had left over from the repipe. This is the only way I can seal the top plate.

Thanks to all the replies. I guess I will press on and do the best I can on the exterior wall top plate.


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## Gary in WA (Mar 11, 2009)

"Therefore, I am not able to secure the top plate portion of the accuvent with staples as I can not reach."--------- foam it in couple of spots, hold for 30 sec.s with stick pressure 'till set. Could you blow the dust/dirt with air nozzle before foam? If needed...

Gary


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