"Swingman" ...
"Dean H." message

The reality is that if the window is farther out of the building than
before, there's really no way it's a tighter fit than the window that was
replaced. In other words, a tighter fit or better seal against the
building
would result in the installer needing to trim something off the sill, not
add to it. The whole thing sounds fishy to me. The company should be
reported, IMHO.

IMO, in order for you to say that was indeed the case, you would have to
know with certainty what kind of window was put in.

It is not unusual, for instance, for a modern vinyl window to be thinner
behind the nailing fin than an old window, thereby possibly leaving a gap
between the new window and the old sill when installed, as the OP
reported.

I'm just going by the original poster's first paragraph. If the gap was
caused by window design then the installer should call it what it is and
not blame the previous installation.
If the previous installation wasn't tight enough, that's the one that would
leave a gap, not the new tight one. The logic of the installer's excuse is
entirely backwards.


In addition, the age of the house could be a factor. Thicker because
framing
lumber was a different dimension, 2 x 6 exterior walls instead of 2 x 4,
etc.

Um, a little quick math here...
2x6 vs 2x4 does not yield a 1/4" gap but more like 2".
Maybe good old fashioned 2x4s that really measured ~2x4 instead of 1.5x3.5
is a better guess.
But again, if that's the reason, the installer should have explained it that
way, not blaming the previous installation.
I guess that assumes the installer even knew what he was looking at.