How do I tell if my building/enclosure is considered “partially enclosed”?

A building is considered “Partially Enclosed” if it complies with both of the following conditions (ASCE 7-16, Section 26.2, “BUILDING, PARTIALLY ENCLOSED”):

1. the total area of openings in a wall that receives positive external pressure exceeds the sum of the areas of openings in the balance of the building envelope (walls and roof) by more than 10%, AND
2. the total area of openings in a wall that receives positive external pressure exceeds 4 ft² (0.37 m²) or 1% of the area of that wall, whichever is smaller, and the percentage of openings in the balance of the building envelope does not exceed 20%

IF EITHER IS NOT TRUE, THE ENCLOSURE BY DEFINITION IS NOT PARTIALLY ENCLOSED.

On occasion, building officials will assume a building originally designed as enclosed to be partially enclosed if storm shutters are not provided, which is a conservative worst-case approach, but is defendable by the fact that there is no written code provision for this and the structure won’t meet the above definition. Also, everything needs to be designed for partially enclosed, roof, connections, walls, foundation, beams, columns, etc. A building won’t stand if only 1 part of it is designed as partially enclosed and not the rest.

Another way to view the two conditions above is as expressed by the following equations:

1. A_o > 1.10A_oi
2. A_o > 4 ft² (0.37 m²) or > 0.01A_g, whichever is smaller, and A_oi/A_gi ≤ 0.20

where

A_o = total area of openings in a wall that receives positive external pressure, in ft² (m²)

A_g = the gross area of that wall in which A_o is identified, in ft² (m²)

A_oi = the sum of the areas of openings in the building envelope (walls and roof) not including A_o, in ft² (m²)

A_gi = the sum of the gross surface areas of the building envelope (walls and roof) not including A_g, in ft² (m²)
EXAMPLE:

Partially Enclosed

However, a building that meets both the “open” and “partially enclosed” definitions should be considered “open” (ASCE 7-16, Section C26.2, “BUILDING, ENCLOSED; BUILDING OPEN; BUILDING PARTIALLY ENCLOSED”).

From the ASCE 7-16 Commentary C26.2 Definitions:

BUILDING, ENCLOSED; BUILDING, OPEN; BUILDING, PARTIALLY ENCLOSED; BUILDING, PARTIALLY OPEN:

These definitions relate to the proper selection of internal pressure coefficients, (GCpi). “Enclosed,” “open,” and “partially enclosed” buildings are specifically defined. All other buildings are considered to be “partially open” by definition, although there may be large openings in two or more walls. An example of this would be a parking garage through which the wind can easily pass but which does not meet the definition for either an open or a partially enclosed building. The internal pressure coefficient for such a building would be ±0.18, and the internal pressures would act on the solid areas of the walls and roof. The standard also specifies that a building that meets both the “open” and “partially enclosed” definitions should be considered “open.”

See also “Enclosed Building” and “Open Building”