Do you do anything extra to seal up the open outside corners on fold-out window flanges? The little sticky patch the manufacturer supplies and a smudge of sealant don’t seem ideal and I wonder if they’ll stand up for 30, 40, 50 or more years.

I’ve gotten in the habit of back-flashing the flange at the corners with a piece of flexible flashing tape like 3M 8067 – it’s thin so it doesn’t bulk up the flange and it’s very sticky.

I start with a 3 in. x 4 in. piece and score the release paper about 1 1/4 in. in along the 3 in. width so it can be removed in two steps.

First step is to remove the 1 1/4 in. piece of paper, fold the tape face-to-face and bond to the jamb of the window.

Second step remove the remaining release paper while the tape is still against the jamb and rather than fold the tape over the flanges – fold the flanges against the tape. This gives you more control. About 1/4 in. to 1/2 in. of the tape will extend above the edge of the flanges so fold that down onto the face of the flange.

Finally, splay the flange out and use something with a thin edge to press the tape tight to the flange/jamb junction; a mini flat bar, thin end of a shingle or my preferred tool—a card cut from vinyl siding—work well.

Then when you install the windows you can stick on the pasties and smear on the sealant the manufacturer calls for.

For a step-by-step demonstration of this process, look back at this article from the Rhode Island FHB House: “Backflashing Fold-out Window Flanges”

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