Why caulk between studs, etc?
I understand that a small amount of air can pass through the gap between two or more side-by-side framing members, but so what? Then that air hits the drywall, which is an air barrier. In the middle of a stud bay, that same air is passing through fiberglass batt insulation (not an air barrier) and hitting the drywall. What’s the difference? For that matter, why caulk the drywall to the top plate? Isn’t the intersection of the wall and ceiling drywall taped and mudded? Isn’t that an air barrier? Further, I always caulk that intersection after primer, but in the past that’s been to prevent hairline cracks in the plaster or gypsum from showing. I can understand sealing between the bottom plate and the subfloor. Someone please help me understand this! I’m sure I’m an idiot but would like someone to prove it.
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Here are a couple of slides from a 2014 DOE's ZERH Program presentation I used to teach, based on the 2012 IECC. It shows the air leakage distribution on exterior walls, not counting the leakage around the openings.
I've also attached a few pics that I found on the web. I hope this helps somehow... Cheers!
The PDF attachment is at the bottom.
That small crack is bigger than it looks, and is a thermal bypass around the cavity insulation.
If the gypsum is made air tight to BOTH of the doubled up framing elements it blocks the thermal bypass, but simply caulking the seam is easier, and likely to be more reliable over time.
One opinion about relying on drywall as an air barrier is here:
Also note that two air barriers will outperform one. For example, prevent air from leaking into the wall cavity from the exterior AND prevent it from leaking from the cavity to the interior.
jeffsch1: I wonder the same thoughts. For example I have taped the seams of the OSB sheathing, covered with house wrapped (not taped). Outside of that I have 1 inch of rigid foam -not taped but with staggered seams (staggered from the OSB seams) The taped OSB is air barrier-despite the new data showing OSB makes a "poor air barrier". The OSB even overlaps the top plate/wall connection of the 1st floor/2nd floor--i.e no seam. Other than the slab/sill plate connection that deserves a good bead of caulk I don't see the need to caulk the top plate of my 1st floor/2nd floor connection. On top of that I'm spec'ing dense pack cellulose. Shouldn't this eliminate my need for caulking all those double studs?