I was reading the installation instructions for my ThermaTru entry door found at:
Check to be sure the framing walls around the opening are in the same plane. Do this by performing a =93string test=94 for plumb.
String Test for Plumb: Attach a string diagonally across the opening from the outside, as shown. The string(s) should gently touch in the center, if not the opening is =93out of plumb=94 by twice that distance and needs to be corrected. Flip the string over itself to check both planes. Fix any problems now.
An =93out of plumb=94 condition is one of the most common reasons door units leak air and water.
*** End Stolen Text ***It seems to me that the same check should be done for windows, but I never saw this mentioned in any window installation instructions. I know that besides checking the opening we should also check the window/ door itself before (and after) cranking down on the mounting screws, but I've never seen this "Same Plane" check mentioned before.
Thoughts?