David Joyce | July 25, 2016

Video // WRB & Flashing, Windows & Doors, Insulation & Air Sealing

Superinsulated Sunroom (3): Flashing an Outie Window


Wide tape spans the many layers of a thick wall to make an air tight and water tight seal


Last week we showed how Synergy Construction installs the window bucks for a thick-wall window install.

At the end of the video we showed them cutting an angle into the foam to slope the sill.

That’s where we’re starting this video.

They also clean up the OSB edges. But clean up the foam dust before peeling and sticking the peel and stick flashing tape to the sill.

Because this is extra wide flashing tape with a single release paper, Calvin begins at one end and works to the other. 

For tape with a split release paper, you can remove one strip and work from the middle outward.

Pull the stretch tape around the corners.

The flashing tape is more than a water barrier in thickly layered construction like this—it is the air seal that spans from the innermost framing to the outside of the foam: 

David: "It’s important to get it to the interior framing member so that we have sealed the layers of the foam to our window opening."

And there are five layers in this assembly.

David: "We pay a lot of attention to our window openings be hey are penetrations in a relatively perfect building. And that’s where all the problems happen."

No need to sweat the bottom corners too much, they are already waterproof. It is mostly a matter of keeping the tape from sticking to itself as you let it fall into position. 

But they do add a layer of tape to bridge any gaps between the jamb flashing and OSB.

 Now, it’s time to set some windows.   


—Thanks to David Joyce, for opening his jobsite to our film crews. Thanks also to Calvin Cutts, PJ Burke, Damien Higgins, and John Albert for working with us and playing through the pain.



For a company focused on energy, I find it surprising there is so much unnecessary framing. No one has ever given me a sensible explanation why framers in MA put in two 2Xs for rough window sills. Five 2Xs between the two windows? Run the header all the way across both windows and use two jacks for the opening. And why all the cripples under the sill? None are needed except for nailing the baseboard. For that you can put them on the flat to get insulation behind them.

It appears that the wall you are working on in the video is a side wall. Why have a header there at all?

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