Air barrier continuity at sheathing/top plate/ceiling transition
Hi all,
Does anyone have advice on how to detail the air barrier at the transition from plywood sheathing to top-plate to ceiling (Intello membrane)?
I was planning to lay down an 18” strip of Siga majvest over the top plate to make this connection (I believe Josh Salinger has used this technique ). The problem I’m having is that my plywood sheathing will extend above the top plate to cover a 14” raised heel truss (without a panel joint landing on the top plate). I’m wondering how I would connect the membrane strip to the middle of a sheathing panel. Also, Siga majvest is crazy expensive, is there a cheaper alternative that is still vapor open and durable enough to stand up to dragging trusses over it?
Or perhaps there is a better way than a membrane altogether?
Thanks!
Adam
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My framers are doing the same thing. I am taping the plywood as my air barrier. What I suggested is we tape the seems up, tape the end of the plywood and then back down the inside of this piece that covers the trusses. Then tape to a horizontal piece of plywood that caps/connects the double walls. They didn't want to have the Intello X there because the framers would be walking those walls while setting trusses.
I'm also interested in seeing what you find out for a strip of 18" material. We bought Mento 3000 for the wrb since it came in double wide, but my walls might be just slightly too call for that I'm realizing...
Thanks Tim. That might work if the plywood is in place before the trusses are installed (so that you have access to the plywood seems).
I’m installing the trusses first since they have overhanging top chords and I thought the plywood would get in the way of dragging.
Adam,
After the trusses are up and as you are installing the last course of sheathing, run a bead of flexible sealant (acoustical caulking or Cotenga HF) on the outside of the upper top-plate. Similarly, connect whatever you are using as a ceiling barrier to the inside of those upper top-plates later on.
Ah yes, thanks Malcolm. The flexible sealant is a great idea, and will be a whole lot easier/less expensive.
As for the ceiling barrier membrane, I’m worried there won’t be much to connect to since I’m only using a single top plate. Will taping the edge of the ceiling membrane still work?
Or perhaps an inexpensive membrane 9” strip like Henry moistop-EZ seal (available locally)?
https://henry.com/residential-and-light-commercial/window-and-door-flashings/moistop-e-z-seal
Adam,
I'd fold the membrane down onto the inside face of the top plate and bed it in a bead of the same sealant.
This is what we did. I used lexel. Don’t forget to tape or caulk the joints in the top plate. We haven’t done the blower door yet but I suspect this technique to work well. As far as membrane goes, Rothoblaas has a great selection of membranes and good prices. We’re using “vapor in” membrane in our northwest Montana climate.
We stop our sheathing at the top of our first top plate, we then place a strip of, self adhered membrane, Siga Majvest SA or Adhero (floppy membrane like Intello would work too, just needs sealant or tape to make the connection to exterior WRB) across the top plate and fold it down over our sheathing by a couple inches and the same on the interior. We then install our double top plate so that we have a traction when placing trusses.
The band of sheathing that covers the truss heel gets installed last and since our air barrier is at the ceiling, the sheathing at the heel is simply in place to keep loose fill insulation from escaping.
Thanks Sommerbros,
That makes sense, stopping the plywood at the top- plate, and then adding another strip over the trusses is probably the most common method im guessing. We decided that extending the plywood all the way with one panel would provide more a bit more structural strength for our seismic zone d, but it obviously wasn’t necessary. We’ll see if I regret the extra steps.
Adam
Adam,
Using the sheathing to tie the top plates to each other, to the studs below, and to the trusses above is a good idea in seismic zones, and those with high winds.
If you can't use the sheathing to tie the entirety of your top plate together, so that it can resist uplift forces, then you can use hurricane ties to tie in the remaining pieces. If you're in an area prone to seismic activity or high winds, the extra structural details can make a huge difference. Some years ago I remember seeing some pics of neighborhoods in Florida after a hurricane had gone through. Some houses were nearly flattened, others were relatively undamaged. The big difference between the two was the use of hurricane ties, properly installed, to keep things from blowing apart in the wind. You can make a hugely more robust structure with those small details if you do it right.
Bill
Thanks Bill, glad to know that details like this can make a big difference. In addition to the full sheathing, I’ll be using Simpson truss screws for hold-down resistance.
I was planning to lay down an 18” strip of Siga majvest over the top plate to make this connection https://winrand.co.za