Hello! First post, however I am a long-time appreciative reader of this site’s articles and forums.

I live in Halifax, NS, Canada. Climate zone 6. A carpenter friend, myself, and my spouse are doing a renovation/addition on our home, and we have a question regarding our exterior building envelope.

From inside-out, we currently have: plastic vapor barrier, 2×6 wall studs, interior cavities sprayed with 1/2lb. open-cell foam, 3/4″ plywood sheathing, Vapro Shield IT wrap. The final buildout will add to that: 1 1/2″ Roxul Comfortboard rock wool insulation, 1″ strapping, and finally 5/8″ wood siding. The roof deck is sprayed out with 2lb. closed-cell foam, 3/4″ plywood sheathing, full Ice and Water, and 24ga. galvalume on the roof (standing seam, unexposed fasteners).

Our windows are “innies,” with flanges on the sheathing plane. We used Vapro Flashing and the sonic welded corners in the window install, caulked the window flanges top and sides, nailed all-around. The house wrap runs right up over the window flanges on top and sides, to the base of the brickmold, with DOW Corning 758 holding it in-place on the sides and left loose on top (for the eventual insertion of a metal drip-cap as part of the metal window flashing system).

It was suggested by another builder that we pick up some 3M all-weather flashing tape to really seal up the joint between the Vapro Shield IT and the window flanges. We have the 4″ tape, but now are scratching our heads about how it should integrate with the metal drip cap and the Vapro Shield IT along the header.

The following order of events makes sense to us…

1. The bottom flange of the window should receive NO 3M tape;
2. the side flanges would get taped vertically, all the way up the window, sealing the Vapro Shield IT firmly to the flange, with the tape extending up past the header;
3. the metal drip cap should then slide in underneath the loose flap of Vapro Shield IT, from edge-to-edge of the top of the window, folding the metal over the corners of the brick mold…

…and here is where we get lost. Should the drip cap be caulked to the sheathing plane? Or just nailed? Both? Should it’s top edge be 3M’ed to the sheathing? Does the drip cap get caulked to the brickmold anywhere? If so, where? When the Vapro Shield IT flap goes back down over the drip cap, should that be DOW Corning’ed, 3M’ed, anything?

We are leaving the exterior insulation/strapping/siding off until Spring, so the idea of just putting on the drip cap and taping the edges sounded appealing for the Winter, while we work on the interior.

However, come Spring, some pretty wide metal flashings are going to have to go around all sides of the windows to cover up that exterior buildout, and we don’t want to find out we somehow painted ourselves into a corner.

A window detail is enclosed to illustrate what we are looking at.

Any advice would be much appreciated!

Thank you!