How you classify your building's openings can change wind loads by 50% or more. Enclosed, partially enclosed, or open - the GCpi makes a huge difference!
Get accurate ASCE 7-22 wind load calculations for your Broward County project.
Get Wind Load CalculationsMinimal openings, sealed tight
Dominant opening on one wall
80%+ of each wall is open
In Broward County's WBDR, all glazing must be impact-resistant or protected to qualify as "enclosed." Unprotected glass is assumed to break in a hurricane, automatically triggering "partially enclosed" classification with GCpi = 0.55. This can add 30-50% to your structural requirements!
Imagine your building is a balloon. When it's sealed (enclosed), air pressure inside and outside stay balanced - the balloon holds its shape easily. But poke a hole facing the wind, and suddenly air rushes in, inflating the balloon and pushing outward on all sides.
That's exactly what happens when a window breaks on the windward wall during a hurricane. The building tries to explode from inside.
Impact-resistant windows aren't just about keeping debris out - they're about keeping your building classified as enclosed. A single broken window can:
Engineers in Broward County face a decision: specify impact-rated glazing and design for enclosed pressures, or use standard glazing and design the entire structure for partially enclosed loads.
Usually, impact windows are cheaper than beefing up every connection, beam, and fastener to handle the higher GCpi. But you need to run the numbers for your specific project!
ASCE 7 defines three enclosure classifications: Enclosed (openings less than 1% of wall area), Partially Enclosed (openings exceed the 1% threshold with specific distribution requirements), and Open (80% or more of each wall is open). Each classification has different internal pressure coefficients (GCpi) that significantly affect wind load calculations.
Enclosed buildings use GCpi = plus or minus 0.18. This relatively low internal pressure coefficient applies when total openings are less than 1% of the gross wall area on each wall, or less than 4 square feet, whichever is smaller. Both positive and negative internal pressure must be checked.
A building is partially enclosed when: (1) Total area of openings on one wall exceeds 1.1 times the sum of openings on all other walls, AND (2) Total area of openings on that wall exceeds 4 sq ft or 1% of gross wall area. This typically occurs when a large door or window fails during a storm.
Partially enclosed buildings use GCpi = plus or minus 0.55, which is 3 times higher than enclosed buildings. When wind enters through a large opening on the windward side, it pressurizes the interior, adding to the outward forces on walls and roof. This can increase design loads by 30-50% or more.
In Broward County's Wind-Borne Debris Region, glazing must be impact-resistant or protected by shutters to qualify as enclosed. Without protection, the building must be designed as partially enclosed. Using impact-rated windows and doors allows the lower GCpi = 0.18 and significantly reduces structural requirements.
Get accurate ASCE 7-22 wind load calculations for enclosed and partially enclosed buildings in Broward County.
Get Wind Load Calculations