No casing window trim options

Question

We're having new Marvin Essential slider windows installed. The trim options our installation contractor offers are drywall return and a few different styles of pine trim/casing.

Our current windows don't have any casing, but also aren't totally drywall return. They have some kind of material about 3/8" thick lining the bottom and sides of the opening (jamb extensions?),

while the top is drywall.

As far as I can tell, the jamb extensions abut the window frame (rather than extending underneath), based on the fact that more of the frame is visible at the top where there's only drywall.

Q1: what is the term for what I currently have here?

Q2: is this still a generally acceptable method for interior trim?

Q3: my contractor says that if I go with some style of (wood) trim rather than drywall return, the windows will be marginally smaller (~0.5 inches). Why would this be the case? Does wood trim typically sit as an extra layer between the frame and the studs?

Q4. Would that be the case (smaller windows vs. drywall return) as well if I can recreate the current visual style with 2022 construction standards?

Q5: if I opt for drywall return from the installers, can I add jamb extensions at the finishing step without ripping out the drywall? The installers will not be doing the finishing ("painter ready").

Answer 1

If you have room for it, you can have the drywall guy wrap the window openings then add the woo trim directly over the drywall, it acting as a shim. The thing to watch for is casement window crank handles. Those usually only allow 3/4" of material under them without crowding the crank body.

If room is too tight for that, then have the drywall guy run the drywall to the window rough opening and set his corner bead to the drywall on one side, and directly to the framing on the other, mudding in only the wall side, so the trim can cover the bead in the opening.

When this was done in homes I have worked in, I used various thicknesses of material to shim the window opening, so when the wood liner was added, the margin around the window was the same. Typically, when a window is set, it is tight on the bottom, and a gap on the sides and top. This will make the margin different if not shimmed ahead of time. Some rough openings are not level, making a gap on one side and not the other, this will also show if not shimmed ahead of time.