How Much Air Sealing Do I Need?
Trying to figure out how much air sealing is needed.
We are building a single story house in central Missouri (Jefferson City are so zone 4c, I think- mixed/humid). It has 2×4 walls and we have spray foamed the exterior walls with open cell spray foam. They also caulked along all the of all exterior walls to the subfloor. Going outwards, it then has house wrap and then HardieBoard siding. It is on a crawl space that has been encapsulated with about 2” closed cell spray foam or more on the inside walls and spray foam is sprayed over the floor joists and sill plate as well. It has a flat ceiling and we will be doing loose fill cellulose up in the attic, and the attic access is from the outside above the insulation level, so no air leakage from inside the house. The insulation isn’t in yet, so I went up to the attic and did “great stuff” spray foam into any holes for wires and also where the interior walls intersect the ceiling, so I tried to seal between the wood and the drywall ceiling from above. I also did a “cap” of great stuff foam over light housings and ceiling fans and tried to seal the bathroom fans similarly as well. All vents go to the soffit or outside. We are using ductless multi-head mini split to heat and cool, so no duct leakages.
—So, my question is:
I was telling my spouse that we should caulk everywhere the drywall meets the floor, the outlets, and the light housings before we put in the plugs, lights, etc to stop any air Leakage going there and up behind the drywall. He says since I did the spray foam up above that this is an unnecessary waste of time and money. I know you can’t have too many air barriers, but he is reluctant to spend time on this unless it really makes a difference. If it is overkill it is not worth the strife. So I am asking for advice. Should we caulk anything now? If so, what. I also wonder if vibration of ceiling fans and bath fans could cause cracks in the great stuff foam that we won’t be able to find under the insulation later.
Thank you all in advance.
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Replies
If you seal all the top plates from the attic side, it's not really necessary to seal the perimeter of the interior drywall. What you're really trying to do is to see the building envelope and not the individual walls themselves. In most homes, the building envelope includes the exterior walls and the upper floor ceiling, then some various things in the crawlspace and/or basement perimeter. When you're done, you want to have a box with no leaks. If you've already air sealed the entire attic floor, which is that upper floor's ceiling, then any leaks into an interior wall still have no where to go since the top of the wall is already sealed.
I would still be careful with any EXTERIOR walls though, since those walls are air barriers themselves. That's where you want to focus any drywall caulking efforts, and don't forget any intersections with those exterior walls where other walls join in. Remember the box of the building envelope, and make sure any possible pathways from the inside of the box to the outside are sealed and you'll be in good shape.
Bill
A blower door test would help you gauge how much more air sealing may be necessary. Add a fog machine (tis the season!) for good measure and you can even start to pinpoint where leaks occur, if any.
It sounds like you've got the main bases covered for a continuous air barrier. The only way to be certain is to test.