Hello all, we had a contractor install new windows on a cottage addition. The exterior is finished, but in an effort to save costs, we plan on finishing the interior ourselves. I'm stumped on how to properly trim and finish the windows on the interior. Any advice or resources would be greatly appreciated.

 

That's a pretty vague question. Are you going to drywall the walls around them? That obviously gets done first. You want painted trim or stained? Are you matching any other existing trim? Got pics of what you are after?

 

My apologies. Yes to drywall around them, and then stained trim, with nothing else to match. This may seem like a silly question, but how to I install trim overtop of the plastic frame around the window?

 

The drywall will get applied to the face of the wall only, and they should router it off around the rough opening.

It looks like your windows have a jamb receptor on all 4 sides. Can't tell how wide it is... 3/4"? Basically, after your drywall is done, you will measure from the back of the receptor to the face of the drywall... that will be how wide your extension jambs need to be. You will rip that wood on a table saw, cut the pieces to length, (these are all square cuts) and insert them into the receptors. If you rip them a 1/8" short you will be able to flush them up with the face of the wall a little easier. Shoot the corners together with a brad/finish nailer. Then shim the sides to the rough opening so they run straight and true... nail to the rough opening every 24" or closer as needed.

Once the jambs are done, put your casing on. The 4 corners get mitered at a 45. You leave a 1/4" reveal around the inside perimeter of the extension jamb to the inside edge of the casing... it creates a 1/4" step.

Nothing gets nailed directly to the window, it gets nailed to the framing around the window.