I would think that the best method would be to remove the whole window peel back the siding and replace it with the same size window with a nailing flange with either the built in channel or j it out.
Removing new construction vinyl windows.
My wife s grandfather owns a business which deals in windows and various other building supplies.
The current windows are builders grade new construction vinyl windows with the nailing flange and built in channel.
The process is simple enough for just about any home owner.
Remove the old sill using chisel and hammer.
Then add 3 4 on all sides to allow some wiggle room to make the window plumb and level.
If you are replacing windows on your vinyl sided home and the old window frame sill and jambs are not damaged or rotted you won t need to disturb.
Watch the removal and installation of a single hung window.
Mark the center of the old sill so the new window will be centered.
How to replace windows on a vinyl sided home.
When you build a rough opening for a new window make it big enough to accommodate the window and a false frame that will finish the rough opening.
I can get a replacement window that is around 91x58 that is a beautiful picture casement vinyl window and has triple pane double argon with faux wood grain.
It is around 91x60.
I just gave a quote for replacing windows in a 1940 s home with double hung weighted windows for just under 1000 each in maryland.
I spec d 3 0 5 6 andersen double hung windows with screens for new construction.
I will be removing a new construction triple window from my home.
In fact no tools are used in this tut.