Question On Sagging Storm Door

[driz]

I have one of those fully framed aluminum doors that serves as both a screen and storm door . It's attached to the outer casing of my entry door and appears to be one solid assembly with the hinges riveted onto the casing. It sags about 1/2" just enough to let the bugs stop by for a snack. I tried loosening the lower mounting screws on the hinge side and tightening the upper one, no luck. What's next, shimming the bottom out?

[HayZee518]

screen door

take two diagonal measurements to see if the casing and door is square.
if it is square then possibly the addition of a bottom weatherstrip would be sufficient.
if it is NOT square, determine what needs to be shimmed to bring the door back into square.