What should I seal before insulation?

[VietGnome]

Trying to hash out the insulation plan for my 30x40x12.

I'll be blowing cellulose into the ceiling at R40. I was originally planning on blowing it into the walls as well, but I'm unsure how viable that it as DIY.

So I'm exploring just doing fiberglass bats. I've seen people recommending spray in foam the entire circumference of each stud bay. That seems like an insane amount of foam.

What should I actually be foaming for best effects? Top/bottom plates, around doors, and any penetrations through walls? Between joists?

And how do I calculate how much foam I'll actually need?

 

[jack stand]

Air sealing is critical especially with fiberglass.
You're goal is to have NO air movement within each student bay, wall and plate penetrations and corners.
Insulation is given it's "R" rating in a sealed box. Anyone who's ever pulled an insulated wall apart can testify to the apparent "dirty air filter" look of fiberglass batts. That air flow is removing your conditioned heat/cooling.
This is why the more dense insulation's have higher insulation values such as Roxull and the foams.

 

[VietGnome]

Air sealing is critical especially with fiberglass.
You're goal is to have NO air movement within each student bay, wall and plate penetrations and corners.
Insulation is given it's "R" rating in a sealed box. Anyone who's ever pulled an insulated wall apart can testify to the apparent "dirty air filter" look of fiberglass batts. That air flow is removing your conditioned heat/cooling.
This is why the more dense insulation's have higher insulation values such as Roxull and the foams.

That was my thought, I just don't know if I should be spraying between studs, or just the top/bottom plates, corners, etc.

I also don't know how to calculate how much I need. I dont think cans of great stuff are an option for the volume I need, and the only other option i see are kits from DAP, etc that are easily over $1000 and calculated in board feet.

 

[PCustoms]

That was my thought, I just don't know if I should be spraying between studs, or just the top/bottom plates, corners, etc.

I also don't know how to calculate how much I need. I dont think cans of great stuff are an option for the volume I need, and the only other option i see are kits from DAP, etc that are easily over $1000 and calculated in board feet.

I spray the "corners" with a small bead. So in each bay, that's 4 stripes of foam.

Get one of these:

https://a.co/d/01bO2HFn

And then some variation of this:

https://www.homedepot.com/p/GREAT-STUFF-PRO-24-oz-Gaps-and-Cracks-Insulating-Spray-Foam-Sealant-341557/202892471

The pro gun is easier to use, let's you dial in a consistent bead and let's you close off a can and come back later. I wish I had bought one years ago.

I get the cans as needed at the orange store, if I was buying a case I might look around for better pricing. Personally would stay away from the "no name" brands.

 

[VietGnome]

I spray the "corners" with a small bead. So in each bay, that's 4 stripes of foam.

Get one of these:

https://a.co/d/01bO2HFn

And then some variation of this:

https://www.homedepot.com/p/GREAT-STUFF-PRO-24-oz-Gaps-and-Cracks-Insulating-Spray-Foam-Sealant-341557/202892471

The pro gun is easier to use, let's you dial in a consistent bead and let's you close off a can and come back later. I wish I had bought one years ago.

I get the cans as needed at the orange store, if I was buying a case I might look around for better pricing. Personally would stay away from the "no name" brands.

So essentially you do the entire circumference of each stud bay? Or am I misunderstanding?

 

[PCustoms]

So essentially you do the entire circumference of each stud bay? Or am I misunderstanding?

Yes. It really doesn't use a lot of foam

Stolen picture, I usually get a bit more of a bead:

 

[Bert_]

See a lot that get caulked also. It does seem like a lot at first. A lot of new construction still has terrible air sealing.

 

[bluedog225]

I forget which one, but one of the foam products marketed as fire resistant will not sustain a flame. The others burn pretty readily.

I think beads of PL premium would also seal the cavity. And provide some additional strength.

I’ve been working with mineral wool lately. It’s nice to work with. And you can cut it with a cheap electric carving knife.

I think to blow cellulose into the walls, you staple up the netting type product. I forget what it’s called. Then you cut a slit and blow into it. Seems pretty straightforward. And I think cellulose is more resistant to air flow than fiberglass.

 

[PCustoms]

I think beads of PL premium would also seal the cavity. And provide some additional strength.

No on both, sorry

 

[jack stand]

As long as you're not filling a cavern, a simple caulking gun (buy a good one) and 11oz. tubes would do what's shown in @PCustoms pic.
I've used cheap latex "painters" caulk but it's probably worth a little better exterior caulk. It's my habit to "wet finger" the bead just after applied. Weather it squishes it in a little deeper or not, it makes me feel better!
I have used a pro gun for this because it's what's in my hand, I prefer the results of a caulking gun better.
BTW. after having several of these gun dispensers over the years and eventually having them gum up no matter how **** I am about cleaning these $40 +/- tools, I've found them on Amazon. 2 for less than one at retail stores AND NAPA (probably any) BRAKE CLEANER is just as effective as the $12 "gun cleaner". They seem to loose their propellant once used and removed from the gun.

 

[JohnX14]

Unless you need to comply with a specific energy code, I'd do fiberglass batts, with kraft faced insulation. You won't be as energy-efficient, but you won't be too far off. You can still do the air sealing. I've been to enough seminars on insulation to draw this conclusion. Led by some industry experts. You can make a lot of arguments for certain aspects of open or closed cell foam, but when you look at the entire effect of all the building components, vapor barrier requirements, engineered lumber, moisture, etc. I would keep it as simple as fiberglass batts, or maybe mineral wool.

 

[Bert_]

I've pulled out the dusty dirty fiberglass batts that have been there for 40 years with no air sealing. They were 3-4 times heavier than they should have been because of all the dirt inside the fiberglass. How did the dirt get there? It got carried in with all the air flowing through.

Kraft paper is a joke as far as air sealing goes. I guess it's better than nothing.

 

[mm08822]

The asphalt on the Kraft paper is the actual vapor barrier on faced product.

Unless the Kraft paper flanges are unfolded and stapled neatly to the stud faces, there won't be any chance of an effective air seal. Speed to completion almost certainly assures there will never be a good seal.

Unfaced Fiberglass batts or rock wool with full height sheets of vb applied after is a much better option.

Sealing at the sill plate and rim joists is still needed.

 

[PCustoms]

Nvr mind. Another simple thread going off the rails

 

[Sturgeon]

A lot of ants here in Montana, Concrete contractor, bless his heart put a lot of saw cuts on are slab. So under the bottom plate the little basterds have a easypessy access. That's even with a two foot band of sheet metal wrapping the base of shop. Anyways, wish I would have made a effort to seal those saw cuts under bottom plates.