Sizing a steel window header 1

[Daniel Berger]

Home-owner question: I am trying to slightly enlarge a basement window. There is no traditional header above the existing windows. Above the existing window is a 2”-thick mud sill on which the first story’s floor joists rest.

I cannot easily add a header w/o taking away significant window space. Would it be structurally sound to 1) add blocking between the joists and 2) add a steel header inside the opening, resting on jack studs. How to size that steel header?

For further information, below is a sketch and here’s additional detail. There are two stories above this basement. The house is from 1905, and unfortunately, I don’t know the type of framing (looks more like platform than balloon since I cannot look up the wall to the second floor). The concrete foundation wall is 7” thick, the mud sill is even wider and extends over the outside of the wall. The wall is 52' long.

 

[KootK]

Would it be structurally sound to 1) add blocking between the joists and 2) add a steel header inside the opening, resting on jack studs.

I feel that the concept is sound.

How to size that steel header?

With help of a registered professional engineer whose hand you can shake and whose wallet you will fatten as remuneration for her services.