I'm replacing some windows in my house. The original window openings were outsized for the rooms, so the replacement windows I've chosen are smaller, which means framing in the part of the opening that I won't be using.

The first window that I'll be replacing was off-center in the wall, so I'll be installing the new window to one side of the opening so that it will be closer to the wall's center. As I see it, I need to create two pieces of framing -- one for the side of the window and one for underneath (I think a single L-shaped piece would be structurally weaker). There are two ways that I could build these pieces: one where the side piece fills the opening vertically with the bottom piece at its side (Figure 1); the other where the bottom piece fills the opening horizontally with the side piece and window resting on top (Figure 2).

Right part fills opening
Figure 1: Side framing piece fills opening

Bottom part fills opening
Figure 2: Bottom framing piece fills opening

Have I considered all the options for how to build the new framing, and is there an advantage for one method over the other?

4 Answers 4


If you were framing this opening from the start, figure 1 is the way it would be done. I would go that direction so it will make sense to anyone working in this area of your home in the future.

Did you consider the possibility of centering the new window horizontally in the existing opening? That may result in a better proportion. In that case I would still use the approach in figure 1 with new vertical sections on both sides extending the entire height of the opening.

  • The original window was off-center, so putting the new window to one side of the opening puts it closer to the center of the wall. But I will be replacing other windows where I'll need new framing on both sides, like you suggested.
    – Niall C.
    Commented Sep 9, 2010 at 19:57

I would suggest you use the method in figure 1. It is conventional, easier and uses less material.


I would use fig. 1. It would give the wall more strength on the side(s). When the new window is installed, it will be a more steady installation for the siding on the outside.


I am assuming that there is a header built into this framed wall that spans the original 'too large' opening. As long as you have no header issues, I would go with figure 2. The reasoning is that, with the header in place, we won't have a structural compression factor in play. My only concerns under these circumstances would be shear and lateral load issues, and figure 2 will allow for the most secure fasting to combat any wind shear issues. Good luck

  • As noted in the accepted answer, Option 1 is the way it would be built if building from scratch. Would you build a brand new wall with option 2 framing? If not, why modify the wall that way - it makes no sense.
    – FreeMan
    Commented Nov 16, 2022 at 12:01

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