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?),

current window bottom corner

while the top is drywall.

current window top corner

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").

  • Trim is used to hide imperfections between the wall and window, that line shown in your picture. It is up to you with what you are happy at looking at everyday.
    – crip659
    Mar 19, 2022 at 12:15
  • @crip659 the line doesn't bother me. I definitely do not want any casing trim on the wall surface adjacent to the opening.
    – Evan
    Mar 19, 2022 at 12:30
  • If you like it, have the installer copy it for the new windows, or have them suggest a similar finish with no trim.
    – crip659
    Mar 19, 2022 at 13:07
  • That's what I'd like to do, but it's not one of their standard options, and I want to get more information before asking for something outside their standard offerings.
    – Evan
    Mar 19, 2022 at 13:34

1 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.

  • Thanks - getting glider windows, so don't need to worry about cranks, but I don't know exactly how much room there will be - may want to go for the option in paragraph 2. Still not sure why the contractor is saying that wood vs. drywall will require a smaller window. Maybe because they use wood thicker than the drywall and are aiming for a similar margin for each style.
    – Evan
    Mar 19, 2022 at 17:03
  • 1
    If they are vinyl windows, the frame is usually 1 1/2", more or less, not including the shim space. Plenty to add just the 3/4" wood jamb, especially if you choose the same thickness as the original, 3/8". If you do have them add drywall, there may still be room to add the 3/8" still... Depending on what kind of margins you wish to see.
    – Jack
    Mar 19, 2022 at 17:16
  • They're fiberglass, so I think the margin may be smaller. This is good information to have when I go back to talk with the contractor.
    – Evan
    Mar 19, 2022 at 17:26

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