Classifying a building as “enclosed” by default, without calculating its actual opening ratio, can miss that the structure genuinely qualifies as partially enclosed — a classification that requires a materially different internal pressure coefficient.
Why Enclosure Classification Is a Calculation, Not an Assumption
ASCE 7-16 defines specific enclosure classifications — enclosed, partially enclosed, and open — based on the ratio of opening area to total wall area on each face of the building. This classification is not a visual judgment; it is a calculation based on actual opening dimensions, and it directly determines the internal pressure coefficient, GCpi, used in the facade pressure calculation.
A building with large openings — bay doors, operable facade sections, or significant glazing that can fail under wind-borne debris impact in certain risk categories — may qualify as partially enclosed even if it appears to function as a conventional enclosed structure under normal conditions.
Where the Default Assumption Breaks Down
Engineers frequently default to “enclosed” classification as the standard case, reserving partially enclosed classification for obviously open structures like parking garages or canopies. This default overlooks that any building with a sufficiently high opening ratio on a single wall — regardless of the building’s general type — meets the partially enclosed criteria under the code’s actual definition.
Why This Classification Materially Changes Facade Load
The internal pressure coefficient for partially enclosed structures is meaningfully higher than for enclosed structures, because a partially enclosed building can experience significant internal pressurization when wind enters through a dominant opening. This internal pressure adds directly to the external pressure the facade must resist — meaning a misclassified building is being designed against a total facade load that understates what the structure will actually experience.
Calculating Classification From Actual Opening Ratios
After clarifying how enclosure classification is determined by opening ratio rather than building type assumption, the fix is calculating the actual opening ratio for every project rather than defaulting to enclosed classification as a starting assumption. Wind Master calculates the correct classification based on actual opening dimensions entered for the project and applies the corresponding internal pressure coefficient automatically, rather than relying on an engineer’s initial visual impression of the building type.
Validate your enclosure classification — Audit your opening ratio inputs