Open, Closed, Partially Open, and Partially Enclosed Structures.

(Negligible Internal Forces)

Partially Open

(Moderate Internal Forces)

Partially Enclosed

(High Internal Forces)


(Moderate Internal Forces)

Wind pressures can destroy a structure in more ways than just blowing it over. When wind is allowed to flow through or around a building, then the pressures generated can be relatively moderate and be limited to pushing and uplift. However, if the conditions are just right, wind can blow into a structure, inflate it like a balloon, and burst it from the inside.

(Image from Simpson-Strongtie – Maybe re-work this ourselves to fit our narrative above?)

When calculating pressures on a structure, it is important to first determine its enclosure classification. As defined in ASCE 7-16, Chapter 26.2, these 4 classifications – Open, Partially Open, Partially Enclosed, and Enclosed – help determine the severity of pressures that may accumulate in and around the structure during a storm.

Classifying a structure may require a bit of calculation and critical thought:

Open & Enclosed Structures

Open and Enclosed structures are the easiest to identify, as long as you remember that the entire structure must satisfy the classification:

An Open structure is one where each wall must be at least 80% open (allowing wind to flow into and through it).