How a house is built
Beams over openings
A beam carries load sideways to its supports. A header is a short beam over an opening. This sketch does not size one.
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The drawing needs WebGL. The notes on the page still stand.
A beam bends. The top is squeezed, the bottom is stretched, and the supports at each end take the vertical load. Deeper beams can span farther, but depth, species, grade, and the supports are a design. A header is the short beam that replaces the studs taken out for a window or a door.
The garage door on this house is the opening that makes the header obvious. The wide windows need the same idea. Highlighted edges in the model mark openings. They are not a beam schedule.