Header is a word used in many contexts so, what is a structural header?
Think of it as a bridge. Its purpose is to bridge a span and transfer weight from above to each end of the span.
The header is extremely important. Gravity works over time, and it certainly works on structural framing to pull it down or apart. The wider the span, the larger the header. And if the header spans a load-bearing location, like over a window or exterior door, it might need to be larger still. And the wider the span the more the support it will need underneath.
For example, the International Building Code says that the necessary span over a 4' space would be a double 2x6" beam, with one stud supporting under each end. And a 6' space would require a double 2x8" beam, with two studs supporting under each end. A load-bearing location might require larger members than that.
Typically the header is a doubled-up beam which fills the space and has a flush nailing surface. That way drywall or exterior wall materials have a smooth, flat appearance and can be attached well.
The load on this wall requires a 2x12" double header over this window!
You can see the double stud support on each side.
Those straps are there to provide what is called a "continuous path," used for earthquake protection. A few strategically placed straps can actually prevent a house from racking during an earthquake. A previous post on that practice can be read here.
This is the third of three windows in the same wall of the same room of the same house.
Do you notice any differences between this photo and the one above?
There is a gap, without a second beam for support filling it.
You can see the center window in this room has intermediate stud supports (called cripple studs) over the window.
This corner window has the same load as the other corner.
Continuous path straps would typically not be placed on the center window, but would on each corner window.
And here the straps are nailed to air! Not sure how much supportive strength that provides ... says he with a wink.
On my report I simply state that this location needs investigation to insure that it is properly completed. And that an evaluation by a structural specialist be recommended.
My recommendation: pre-drywall inspections are the only time a house can be seen in a skeletal condition. Once the drywall is up a multitude of sins can be covered. Hence the so-called "pre-drywall" inspection need! Following that it is important to have a final inspection just prior to the final walk through. Together the two inspections provide a lot of information, and a lot of peace of mind.