Great rooms with high ceilings and walls full of windows have become popular in contemporary house design. But for the unprepared builder, a 16- foot-high wall can spell big headaches. When a strong wind hits an underdesigned wall, excessive flexing and racking may cause problems ranging from cracked plaster and stucco to cracked or rattling glass. To prevent these headaches you need to understand how structures react to wind loads (see Figure 1). All walls have to resist three types of forces: flexing, which acts perpendicular to the wall, pushing or pulling it in or out; shear, which acts in the plane of the wall to cause racking; and normal gravity loads. Most builders are familiar with gravity loads. In this article I'll