Spray Applied Air Sealing Other Than Spray Foam?
I’ve had lots of questions recently. We are nearing the end of our framing. I’ve been working with the framers on some of the details to make a continuous air barrier path from the exterior sheathing to the inside of the ceiling. Because we are using parallel chord trusses and a girder beam, our gable walls are built all the way to the roof. I talked to the framer about taping the sheathing to the top plate so I can connect to it on the inside. Unfortunately, when I got on site today, I realized it got missed and they have already started sheeting the roof. I’m trying to figure out what to do to connect the exterior sheathing to the inside now.
My thoughts are to spray the underside of the top plate where it meets the interior side of the plywood. I’m wondering what options there are for this if I can avoid spray foam? 475 has the Aerofixx kit, but it’s $700 and seems overkill for this smallish job.
Any other options or thoughts on how to seal up this joint? I’m hoping on the other end of the house we get it right, he hasn’t done the trusses or roof deck yet.
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The other idea I had was to tape the first foot or so of the roof sheathing to use that to make continuity. This may be achievable.
Based on your description I understood your original plan would have allowed for the air sealing parallel with the ceiling and allow a vented attic. If that is the case, you can try to seal from the inside with a barrier attached to the underside of the bottom chord and sealed to the vertial part of the top plate.
If you plan on a conditioned attic, google Monopoly Framing and Matt Risinger. He does this all the time. If you alreay have rafter tails, watch this on how Scott True in TX seals the exterior envelope at the roof deck and soffits: https://www.youtube.com/watch?v=fjwjeoLi6X0
We are sealing from the underside. The difficulty is making the transition from outside to inside.
The other major complications is the beam that penetrates the air barrier.
You’ll also need a compressor for it. My brother bought the kit and found with an underpowered compressor it worked well as a caulking gun in tight spaces, but not as a sprayer.
However, a decent chunk of the expense is in the tubes that come with the kit.
One alternative is to have them send a can of one of the two the kit comes with instead, it can be spread with a brush. My brother had decent, is messier than he hoped for, results.
Do it soon, they don’t ship once it gets cold.
If doing it by hand, how does it compare to prosoco or zip liquid flash? My concern with those was caulking over head and it dripping down rather than being able to get it in the crevices
I’m afraid I don’t know, he wasn’t using it overhead.
Prosoco and ZIP liquid are both pretty thick. They're used all the time to detail overhead, like window and door openings.
Some of the fluid WRB can be spray applied. Don't know if they will sell you small quantity though.
Probably your simplest is pick up a pail of duct seal mastic and a stiff brush. Apply liberally. For any big gaps, put fiberglass mess tape first before the mastic.
Now that is a new one I haven't heard before. Good thought! Is that stuff a little flexible when it's all dried?
The consistency is closer to Alex+ than any liquid flash. I have some decade old stuff on ducting here and still seems somewhat flexible. Not much stretch to it tough.
For the gable end, you need to install blocking along the truss lower chord. I would install these so they drop about 1" bellow the truss. This will give you a nice solid backing for the interior vapor retarder. You can air seal the blocking from the top with a foam gun.
For the walls the trusses rest on, I would tape the sheathing to the top plate on the inside of the sheathing. The top plate can now carry your air barrier to the inside.
This is really one of those where you get all the blocking in and get a spray foamer out to do these plus any rim joists.
For the ridge beam this might be a good starting point:
https://www.greenbuildingadvisor.com/question/vaulted-ceiling-ridge-beam-sealing-at-drywall-intersection
Make sure to tape along the bottom of the ridge beam plies. They might look tight but a small gap times 30' means a pretty big hole.
Try to get a blower test down once your air barrier is up before any drywall or insulation goes in. This will let you easily find and fix any left over air leaks.
This ridge beam is all tucked up inside the trusses. My intent was to use intello on the underside of the trusses as the air barrier. And it would carry right under the beam. The difficulty is making the connection to the outside of the gable walls. And on the South end, the beam penetrates the wall for an overhang. I don't think the Dense pack guy wants to put the intello on before insulation, so I can't blower door until that's up. It might be easier to try and air seal the inside of the gable wall, at least on the south end. The bottom plate is not exposed on the sides anymore though. Then I could just carry the intello up the inside of the gable walls as an air barrier to the underside of the trusses.
If the beam is above your air barrier, you don't have to tie it into anything, even at the overhang.
See my earlier post on how to deal with the gable ends.
Cellulose can be installed through Intello. You can use insul web to form the vent space, the air while denspacking can escape through there. You can patch the holes through the intello with tape after they are done.
This would let you get the ceiling air barrier up before any insulation and test.