How a house is built
Wind and earthquakes
Wind and earthquakes push sideways. Floors share that push with braced walls. This sketch does not show the nailing.
Arrow keys turn the house. Plus and minus, or the zoom buttons, change the zoom. A horizontal drag turns it after you tap the drawing. Reset view returns to the step camera.
The drawing needs WebGL. The notes on the page still stand.
Gravity goes down. Wind and earthquakes push the house sideways, and they try to slide it or tip it. Floors and roofs can act as stiff diaphragms that hand that push to walls which are braced to take it. A shear wall uses its sheathing for that push and is held down at the ends so it does not lift. A moment frame resists by bending of beams and columns, which is useful when a wall cannot be solid.
The Puget Sound region is not a low-seismic place. The design category comes from the site and the code edition, not from this drawing. The model shows walls that could be braced. It does not show hold-downs, nail spacing, or a frame.