I am replacing my current windows with new construction windows. Because I am in a historic district I need to keep the same size windows (opening size) and exterior molding. My plan is to remove the exterior molding up to the j-channel (leaving the j-channel), installing the new window, and then installing new exterior molding to match the current size that is there now. After I remove the old windows, the rough opening will be too large… i.e. I think if I purchase a new window to fit the rough opening, I would not be able to have the same size molding which is a requirement of the historic district.
Am I correct that I will need to build up the rough opening to provide a place for the new construction window to nail into and also allow enough room for the exterior molding? And what is the correct size windows I should order? Is 30" x 63 1/2" correct?
I plan on using Andersen 400 Series windows like this although they will need to be custom sized.
Best Answer
Yes, I think your plan is correct if you mean to shrink the rough openings. I'd be careful to only shrink as far as necessary, though. I'm very familiar with Andersen 400 series windows, and I think you could incorporate the outer vinyl-wrapped jamb rib into the width of your current casing. This means that you may only need to shrink your rough openings 3/4" or so.
At my previous home, circa 1956, I did work like this using 400s. I laid 3/4" thick vinyl stock over the mounting flanges and caulked it to the vinyl exterior jamb rib so that they appeared to be a continuous unit, with the rib protruding about 1/4". Actually, I caulked it to the window, the wall, and the J-channel and used no other fasteners. It looked nice and worked well for the decade I was there.