Should I fill in gap between window frames?

Question

We are getting new windows. I decided to refinish the trim (from the 60's, but still in good shape other than the lacquer being gone). I removed the trim and found a gap between the frames of adjacent windows (see pic and pardon the chicken scratch). I was told this is normal.

I am concerned that when I nail the trim on the sides of the frame the frame will move (it wiggles a little already). Should I fill the gap with thin strips of plywood, secure the frame some other way, or is it fine as is?

Answer 1

Filling the gaps with wood will cause your windows to jamb as the seasonal change of humidity. I would not fill with a solid for this reason.