The Hurricane Zone

What does building in Miami-Dade High-Velocity Hurricane Zone require?

An envelope in Miami-Dade's High-Velocity Hurricane Zone has to resist wind pressure and impact without failing, and every product in it carries a Miami-Dade Notice of Acceptance. Here the aluminium window-wall is rated to ±130 psf and impact-rated throughout, and every roof opening is framed with added steel rather than left to span.

What a Notice of Acceptance is

Miami-Dade County operates the only glazing product-approval programme in the United States that carries the force of county code. A Notice of Acceptance — NOA — is the county’s written confirmation that a window or curtain-wall system has been tested to High-Velocity Hurricane Zone standards and may be installed in Miami-Dade. Without one, the system cannot go in. The approval is product-specific: it names the manufacturer, the series, the configuration, and the tested pressure range. At Leslie House the aluminium window-wall carries an NOA for the ES-8000 series.

What design pressure means

Design pressure is the wind load a glazing assembly must resist without failure, expressed in pounds per square foot. The positive number is pressure inward — wind pushing against the glass. The negative number is pressure outward — the suction that forms on the leeward face of a building during a hurricane, and is often the larger force of the two. A rating of ±130 psf means the system is tested and approved to withstand both directions at that magnitude. The ES-8000 window-wall carries that rating on this house, and the product approval is on file.

Impact rating in place of shutters

Miami-Dade’s High-Velocity Hurricane Zone requires the building envelope to remain weather-sealed after the first impact. A glazing system that shatters admits wind-borne debris, changes the internal pressure of the building, and can contribute to structural failure of the roof. Impact-rated glass uses a laminated interlayer that holds the pane together on impact. On this house the glazing is impact-rated throughout — there are no removable storm panels and no roll-down shutters. The glass itself is the protection, and the NOA is the document that confirms it has been tested as such.

Roof openings and added steel

Cutting an opening through a structural roof is not the same problem as setting a window in a wall. The roof carries load — the dead load of the assembly and in a hurricane zone the wind uplift that acts on the entire plane. Every opening is a penetration through a waterproofed assembly, so the edge of each opening has to be sealed as well as structurally framed. At Leslie House each roof opening is framed with added steel rather than left as an unsupported span. That steel is what the glass and the waterproofing are set into. On a building in the High-Velocity Hurricane Zone, a roof opening is a structural decision before it is a daylighting one.