We are finishing our basement and would like to install 4 new hopper windows onto the front side of the house. My question is what is the largest reasonably sized window that can be cut from the concrete without degrading the integrity of the house, assuming that 4 windows are being added to the front of the house, one under each first floor window (new basement windows would be no wider than the existing 1st floor windows).

When we laid out approximately where the windows would go (underneath each of the 1st floor windows) and used the width of the existing hopper windows we have (32"), they all span 2 joists. Reducing the width of the window results in only 1 of the 3 spanning 2 joists.

An idea I came across is the possibility of adding something like a steel angle bar that could be inserted to replace the wood sill and overlap onto the concrete by 8 to 10 inches. The steel angle bar of beam would support the joists and everything above them and the concrete would support the angle bar/beam.

Any thoughts on this idea or any other suggestions so that we do not compromise the structural integrity of the house, but maximize the window size.

1 Answer 1


In terms of vertical load coming down, there would be little load under the first floor windows as they always have a header above the window to spread the load to jack studs on the side of the windows. In addition, there are full height king studs next to the jack studs that extend to the top plates.

There may be cripple studs under the window to help reduce any small sagging of the window frame. Your steel angle bar may be needed to support this and the floor joists above your basement windows, depending on how much vertical dimension you want to allocate to this.

If I were doing this, I would determine the length of the floor joists and calculate the square footage supported by the joists above a window. Then use the code required load (typically 40 pounds per square foot for residences) to determine what your basement window header must support.

This link shows how to calculate load: loads-on-headers

And this link shows the beam size required for a certain load: load table

  • Thanks for that input. Our contractor suggested treating the basement openings like regular windows. So he would install a header above the window with jack/king studs on either side to allow the load to be spread out and not sit totally on the top of the window. He suggested a 2"x6" or 2"x8" header to accomplish distributing the load and avoid any future problems. He noted that the cripple studs under the first floor windows do not carry much weight. Any thoughts on this approach?
    – Nick
    Commented Mar 17, 2013 at 14:27
  • 1
    That's what I was trying to say, with the detail that guessing at the header is a guess rather than a calculation. As an engineer I like to do some sanity checks myself. I have added a couple of references to help you get started. Commented Mar 17, 2013 at 22:16

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