How should I select and install window trim?

Question

We've removed the existing drywall on an uneven wall, along with the trim around a window on this wall.

When we're done making the new wall plumb and even, the window will be more recessed than the new wall.

Here's an image of what I've got:

1. What are the components that I've marked with a question mark?

2. I think I should be installing our backer board up to the outline of the rough opening, is that correct?

3. Will I need to extend out the "?" components and the sub-sill to be flush with the new backer board? If so, can I simply cut pieces of wood to size and nail them onto the existing pieces?

4. We will be tiling all around this window. The tile is 3/8" thick. Do I need to use thicker trim pieces to account for the thickness of the tile that will be cut around it, to ensure that the trim is proud of the tile? (I am assuming that I should be installing the trim before the tile.)

5. Should I fill the gap around the window with some kind of sealant or insulation? There doesn't appear to be anything there right now.

6. I want to use wood for the trim. What type of wood is recommended?

Answer 1

What is the wooden frame around my window?
That's the window "jamb".

Should the wallboard terminate at the rough opening?
Yes. You don't normally extend your wallboard all the way to the jamb so you have room to insulate, etc.

Will I need to extend the jamb to be flush with the wallboard?
Yes, extension jambs are often needed with retrofit construction. Ideally your jamb will be a uniform distance behind the wallboard all the way around. If it varies by more than 1/8" I'd address that.

Do I need to use thicker trim to account for the thickness of the tile?
This is entirely a question of design preference. Normally, tile isn't as thick as the standard trim and therefore whatever is installed elsewhere in the home works fine.

Should I fill the gap around the window with some kind of sealant or insulation?
Yes. Modern practice is expanding foam of the "low expansion" variety. You don't want to bow and bind your window.

What type of wood trim is recommended?
Again, design preference. It can be stained or painted, hardwood or softwood, or whatever you like. It's not exposed to weather, but consider whether it'll be subjected to moisture and choose accordingly.