Enclosed Structures Explained
Determining whether a structure is classified as an enclosed building is a key step in wind-load design. The enclosure classification determines the internal pressure coefficient (GC pi) and therefore affects how much internal wind pressure is considered when sizing components like walls, windows, doors, roofs, and connections.
Definition
(ASCE 7-16 )
An enclosed building is a structure that does not meet the definitions for “open” or “partially enclosed” buildings. In practical terms:
- No wall (including the roof) has an opening larger than 4 ft² (≈ 0.37 m²) and no opening is larger than 1% of the area of the wall in which it is located.
- All windows, doors and other openings are considered part of the building envelope (and assumed closed during wind events).
Because the openings are small and dispersed, the interior is relatively sealed against major ingress or egress of wind.
Engineering Interpretation & Design Implications
In an enclosed building, wind cannot freely pass through the structure, so internal pressures remain moderate and predictable. The building envelope stays mostly sealed, and the dominant loads come from external pressures acting on walls and the roof.
Designers use enclosed internal pressure coefficients (GCpi ≈ ±0.18) in both C&C and MWFRS calculations when openings are small and well distributed. Maintaining the integrity of doors, windows, and wall systems is crucial—if an opening fails, the building can quickly behave as partially enclosed, leading to much higher internal pressures.
Even in enclosed structures, engineers must carefully detail roof-to-wall connections, anchors, and uplift resistance, as external forces can still be severe in high-wind environments.
ASCE 7-16 Guidance on Enclosure Definitions
According to ASCE 7-16 Section C26.2, the definitions of enclosed, open, and partially enclosed buildings are specifically intended to guide the selection of the correct internal pressure coefficient (GCpi).
All other structures that do not clearly meet one of these three definitions are classified as partially open by default. These include buildings with large openings on multiple walls—such as parking garages, where wind can pass freely through but the structure does not satisfy the strict “open” or “partially enclosed” criteria.
For such partially open structures, the internal pressure coefficient (GCpi) is typically ±0.18, and these pressures are applied to the solid portions of the walls and roof.
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Last Update: December 2, 2025