I have a few french that go to the outside in my house.
They look like below, the right door swings out while the left door typically remains closed.
In the above photo, the area circled in red is shown in greater detail below – as seen when looking up. You can clearly see that the door does not make contact with the insulation at the top-left corner of the right door.
In dire-emergency during the wildfires, I covered all of the insulation seams with masking tape to prevent smoke from pouring in. This was effective but not a long term solution.
I've tried closing the left door to different degrees. Shoving it in as far as possible vs closing it only so it is as straight as possible in alignment to the door frame. Neither of these situations has helped.
I am looking for the most effective long-term solution to fixing the air gaps that still allow for opening and using the doors.
Best Answer
You found the weak link in weatherizing French doors. I've found that it's as much art as science. Where the two doors meet the jamb is often a problem.
In the pic it appaears that the weatherstrip above the right door is offset from the vertical strip on the left. Did you try simply repositioning the weatherstrip where you have the gap. Sometimes the weatherstripping has peel and stick adhesive on the back side. See if you can reinstall it to conform to the door and fill the gap.
If that doesn't work your local home store should have any number of pliable insulation strips that you can attach to the exizting strip in that corner. At worst, replace the entire weatherstrip - they're pliable and can be made to fit.