Aluminum storefront framing systems in Broward County's High Velocity Hurricane Zone must resist design wind pressures of +65 to +100 psf while passing large missile impact testing. This guide covers mullion depth selection, glazing capture methods, anchor engineering, vestibule pressure design, and the critical challenge of simultaneously meeting Florida Energy Code and hurricane impact requirements for commercial fenestration.
Permit Alert: Broward County HVHZ requires all storefront systems to carry Florida Product Approval with large missile impact certification per TAS 201/203. Systems approved for non-HVHZ only will be rejected at plan review regardless of DP rating.
How building height, exposure, and zone placement drive DP ratings from manageable to extreme
Design pressure (DP) is the calculated wind load a storefront system must resist without failure, expressed in pounds per square foot. In Broward County's HVHZ, the basic design wind speed of 170 MPH (per ASCE 7-22 Figure 26.5-1B) creates component and cladding pressures that vary dramatically based on the storefront's position on the building envelope. A ground-floor storefront in the interior zone of a 30-foot building in Exposure B may only need DP +55, while the same system at a corner zone on the 10th floor of a coastal high-rise in Exposure D faces pressures exceeding DP +110.
The critical distinction in Broward County is between HVHZ and non-HVHZ areas. Broward's HVHZ boundary runs roughly along I-95, with everything east falling under the High Velocity Hurricane Zone. Storefront systems east of this line must carry product approvals tested to TAS 201 (large missile impact at 50 fps with a 9-lb 2x4 timber) and TAS 203 (cyclic pressure endurance of 4,500 positive and 4,500 negative cycles). West of I-95, standard Florida Product Approval suffices, though the design wind speed remains 170 MPH throughout the county.
The structural backbone of every hurricane-rated storefront is its vertical mullion
Vertical mullions carry the full wind load from each lite of glass to the head and sill anchors. In Broward HVHZ, where design pressures routinely exceed +65 psf at ground level, standard 4.5-inch commercial storefront mullions manufactured from 6063-T6 aluminum extrusion are often inadequate for spans beyond 7 feet. The controlling factor is typically deflection, not stress. ASCE 7-22 limits storefront mullion deflection to L/175 of the span under design wind load, meaning an 8-foot mullion can deflect no more than 0.549 inches. At +75 psf on a 5-foot tributary width, that 8-foot mullion experiences 3,000 lbs of total wind force.
Mullion gauge (wall thickness) matters as much as depth. A 6-inch mullion at 0.125-inch wall thickness provides a moment of inertia approximately 30% lower than the same profile at 0.187-inch thickness. For HVHZ projects where DP exceeds +70, engineers typically specify the heavier gauge to maintain adequate stiffness, even though the lighter gauge may satisfy stress criteria. The heavier section also provides greater pull-out resistance at screw-chase connections for mechanically captured glazing.
| Mullion Depth | Wall Gauge | Ix (in4) | Max Span @ DP+65 | Max Span @ DP+80 | Max Span @ DP+100 |
|---|---|---|---|---|---|
| 4.5" (Standard) | 0.125" | 3.2 | 6' - 8" | 5' - 10" | 5' - 0" |
| 6.0" (Heavy Duty) | 0.125" | 6.8 | 8' - 6" | 7' - 8" | 6' - 6" |
| 6.0" (Heavy Duty) | 0.187" | 9.1 | 9' - 4" | 8' - 6" | 7' - 4" |
| 7.5" (HVHZ) | 0.187" | 14.6 | 11' - 2" | 10' - 0" | 8' - 10" |
Horizontal mullions (transoms) deserve equal attention. In hurricane zones, horizontal members must resist the full negative (outward) wind suction without relying on the glass for lateral stability. This contrasts with non-hurricane applications where the glass often braces the horizontal mullion. For Broward HVHZ, horizontal transoms at storefront head heights of 10 to 12 feet typically require 4.5 to 6-inch depths, depending on the unsupported span between vertical mullions.
Single continuous aluminum extrusion with no thermal barrier. Offers maximum structural integrity because the full cross-section transfers load. U-factor typically ranges from 8.0 to 10.0 BTU/hr-ft²-°F for the frame alone. Best suited for unoccupied commercial spaces or projects where spandrel panels offset fenestration thermal losses through area-weighted averaging.
U-frame: 8.0-10.0Two-piece aluminum extrusion bridged by a structural polyamide thermal barrier (typically 6/6 nylon). Reduces frame U-factor to 4.0-5.5 range. In Broward HVHZ, the thermal barrier must transfer full shear load under cyclic wind pressure. Requires verification that the thermal break maintains structural capacity through TAS 203 cyclic testing. Higher material and installation cost, but often necessary to meet Florida Energy Code requirements.
U-frame: 4.0-5.5Florida Energy Conservation Code (7th Edition, based on IECC 2021) requires commercial fenestration in Climate Zone 1 (all of Broward County) to achieve a maximum assembly U-factor of 0.50 and maximum SHGC of 0.25. Hurricane-rated storefront systems face an inherent conflict: the heavier aluminum framing needed for HVHZ wind loads increases the frame's thermal conductivity, while laminated impact glass adds weight that demands even heavier framing. Three strategies resolve this tension: (1) specify thermally broken profiles with structural-grade polyamide breaks of 0.375 to 0.500 inches; (2) use high-performance low-E coatings on the laminated interlayer to boost center-of-glass performance; (3) employ area-weighted averaging per ASHRAE 90.1 where opaque spandrel panels with low U-values offset the higher U-factor of storefront sections.
Two fundamentally different approaches to keeping glass in the frame under 170 MPH winds
How glass is secured within the storefront framing determines the system's failure mode under extreme wind pressure. In Broward County's HVHZ, where large missile impact strikes the outer lite and cyclic pressure flexes the entire assembly, the glazing retention method must maintain positive engagement through thousands of pressure reversals. Two primary approaches dominate: mechanically captured glazing using aluminum pressure plates and setting blocks, and structural silicone glazing (SSG) using engineered adhesive bonds.
Aluminum pressure plates secured with stainless steel screws at 6 to 9 inch spacing compress neoprene gaskets against the glass perimeter. Provides positive mechanical restraint independent of any adhesive bond. Most inspectors and plan reviewers in Broward prefer this method because failure is visible and testable. Requires exposed aluminum caps on the exterior or interior face.
Preferred for HVHZDOW 795 or equivalent structural sealant bonds glass to the mullion bite surface with calculated adhesion. Provides flush exterior aesthetics with no protruding pressure plates. Minimum bite dimension per ASTM C1401 calculation with 4:1 safety factor on design wind pressure. Must pass TAS 201 and TAS 203 as a complete system. Requires climate-controlled application above 40°F.
4:1 Safety Factor RequiredCombines structural silicone primary retention with mechanical clip backup restraint. The SSG bond carries day-to-day wind loads and thermal movement, while discrete stainless steel clips engage only if the silicone bond degrades. Provides both aesthetic benefit and mechanical redundancy. Increasingly specified for high-profile Broward HVHZ commercial projects where flush aesthetics are critical.
Best of BothThe storefront perimeter anchorage transfers all wind loads from the aluminum frame to the building's primary structure. In Broward HVHZ, anchorage design must account for combined inward pressure, outward suction, and impact-induced shock loads. Every anchor connection involves three failure modes: anchor pull-out from the substrate, anchor shear at the fastener, and local bearing failure in the aluminum frame. The controlling mode depends on substrate material, anchor type, edge distance, and embedment depth.
Sill members carry dead load of the glass plus the horizontal wind reaction at the base. Use 1/4" minimum stainless steel wedge anchors into concrete slab or structural steel with shim-space grouted. Tightest spacing at corner zones where Zone 5 pressures apply. Critical: maintain minimum 1.5" edge distance from anchor centerline to concrete edge to prevent blow-out. Verify slab reinforcing does not conflict with anchor locations.
Head anchors resist outward suction (the critical load case) and must accommodate vertical deflection of the structure above. Slotted anchor clips allow up to 1/4" vertical movement while maintaining full lateral load transfer. For steel structures, weld or bolt clip angles to the steel beam with engineered connections. For concrete, use post-installed anchors verified per ACI 318 Chapter 17 with seismic qualification per ICC-ES AC193.
Jamb anchors transfer horizontal wind reactions at vertical mullion ends. Wider spacing is acceptable because jamb loads are typically lower than sill/head loads. Use stainless steel angles or clips with minimum two fasteners per anchor point. When adjacent to masonry walls, use through-bolts with back plates rather than expansion anchors to prevent block face blow-out.
ASCE 7-22 Zone 5 corners experience wind pressures 1.5 to 2.0 times the interior zone value. Anchors within the corner zone width (10% of building least dimension or 3 ft minimum) must be spaced at 60-75% of the interior zone spacing. For a system designed at 12" o.c. in the field, corner zones require 7-9" spacing. Document corner zone boundaries on shop drawings.
Commercial storefront vestibules in Broward County present one of the most complex wind engineering challenges. The vestibule is a pressure transition zone between the building interior and the hurricane environment. When both doors are closed, internal pressure is controlled and relatively low. The moment the outer door opens, whether by a person, an automatic operator, or wind force, the vestibule instantaneously pressurizes to near-external wind pressure. This pressure wave then acts on the inner door and the vestibule sidewalls.
The design implication is severe: the inner vestibule wall and inner door must be designed for the same DP rating as the exterior building envelope. Many designers incorrectly treat the inner wall as an interior partition with no wind load requirement. In Broward HVHZ, this error creates a direct breach path: if the outer door is compromised, the inner wall becomes the building's primary wind barrier. Failure of this inner wall converts the entire structure to a partially enclosed condition, dramatically increasing internal pressure on the roof diaphragm and all other building components.
Automatic sliding door operators for Broward HVHZ must include wind-lock mechanisms that engage when wind speed exceeds the operator's rated capacity. Standard commercial operators fail at 50-60 MPH. Hurricane-rated sliding operators from manufacturers like Besam or NABCO offer wind-lock ratings to 110+ MPH. The track assembly must resist uplift from negative pressure and the panels must be impact-rated laminated glass. When the wind-lock engages, the door essentially becomes a fixed storefront panel, and the mullion framing must support it as such.
Wind-Lock: 110+ MPHThe vestibule header span is often the widest unsupported storefront member in the building because vestibule entries typically range 8 to 12 feet wide without intermediate mullion support. This header must carry not only the wind load but also the dead load of any signage, canopy, or transom glass above. In Broward HVHZ, headers spanning more than 8 feet typically require steel tube reinforcement (HSS 4x4x1/4 minimum) within the aluminum frame to achieve adequate stiffness at L/175 deflection limits.
Steel Reinforcement TypicalGetting a hurricane-rated storefront system approved in Broward County requires navigating both state-level product approval and local plan review. The process differs substantially from non-HVHZ jurisdictions. Storefront manufacturers must first obtain a Florida Product Approval (FPA) or Miami-Dade NOA (which is accepted throughout the state, including Broward HVHZ) through accredited testing laboratories. The product approval must list the specific DP rating, impact classification, water resistance rating, and air infiltration rate for each frame configuration and glazing combination.
During Broward County plan review, the structural engineer of record must demonstrate that the specified storefront system's approved DP rating meets or exceeds the calculated component and cladding wind pressure at every location on the building envelope. This is not a single number: the engineer must map the building envelope zones per ASCE 7-22 Figure 30.3-1, calculate pressures for each zone, and verify the product approval covers each condition. Corner zones (Zone 5) near building edges often govern the entire system selection because their higher pressures may require a different mullion depth or narrower spacing than the interior zone.
Storefront systems in Broward County HVHZ typically require DP ratings between +60 and +100 psf depending on building height, exposure category, and wall zone placement per ASCE 7-22. Ground-floor storefronts in Exposure C at 15 feet above grade commonly require DP +65 to +75 psf for Zone 4 (interior) and DP +85 to +100 for Zone 5 (corners). Multi-story buildings see increasing pressures with height: at 60 feet in Exposure C, Zone 4 pressures reach approximately DP +80 and Zone 5 can exceed +110. All systems in the HVHZ must also carry large missile impact certification per TAS 201 with 9-lb 2x4 lumber impactor at 50 fps.
Thermally broken storefront framing includes a polyamide or polyurethane thermal barrier between the interior and exterior aluminum sections, reducing heat transfer and improving frame U-factor from approximately 9.0 to 4.5 BTU/hr-ft²-°F. In hurricane zones, the thermal break must be engineered to transfer full wind load shear across the barrier without separation or creep under cyclic loading. This typically requires wider thermal breaks (0.375 to 0.5 inch) with higher-density polyamide and mechanical interlocking profiles to maintain structural integrity through TAS 203 cyclic pressure testing of 9,000+ total cycles.
Mullion depth directly determines the section modulus and moment of inertia, which govern bending resistance and deflection under wind load. A standard 4.5-inch mullion in 6063-T6 aluminum at 0.125-inch wall thickness handles approximately DP +50 psf at 5-foot spans (governed by L/175 deflection). Increasing to a 6-inch depth raises capacity to roughly DP +75 at the same span. For Broward HVHZ requiring DP +65 or higher, mullion depths of 6 to 7.5 inches with 0.125 to 0.187-inch wall thickness are standard. The moment of inertia scales roughly with the cube of the depth, so a 50% increase in depth yields approximately 3.4x the stiffness.
Hurricane-rated storefront systems in Broward HVHZ typically require anchor spacing of 9 to 12 inches at sill and head members, and 12 to 18 inches at jamb members. Corner zones per ASCE 7-22 may require reduced spacing of 6 to 9 inches to handle the elevated Zone 5 pressures. Anchors must be stainless steel (316 grade for coastal exposure) or hot-dip galvanized, minimum 1/4-inch diameter concrete expansion or adhesive anchors with verified embedment depth per ACI 318 Chapter 17. Edge distance must be maintained at minimum 1.5 inches from anchor centerline to prevent concrete blow-out. All anchorage must be designed to transfer the full component and cladding wind pressure from the storefront framing to the building's primary structure.
Yes, structural silicone glazing (SSG) is permitted in Broward County HVHZ when the complete system holds a valid Florida Product Approval or Miami-Dade NOA covering hurricane impact and cyclic pressure performance. The structural silicone must maintain a minimum bite dimension calculated per ASTM C1401 with a safety factor of 4:1 on the design wind pressure, meaning if the DP is +75 psf, the silicone joint must resist +300 psf before failure. SSG systems must pass TAS 201 large missile impact testing and TAS 203 cyclic pressure testing as an assembled unit. Many structural engineers in Broward prefer mechanically captured glazing in HVHZ because it provides a positive mechanical connection that does not degrade with UV exposure, temperature cycling, or improper surface preparation.
Vestibule design requires addressing internal pressure equalization, door operation under differential pressure, and structural continuity at the header-to-storefront transition. When both doors are closed, internal pressure is minimal. When the outer door opens during a storm event, the vestibule experiences full external wind pressure internally, creating a pressure wave that acts on the inner wall and inner door. The inner vestibule wall must be designed for the same DP rating as the exterior envelope. Automatic door operators must include wind-lock features rated for 90+ MPH. The vestibule header must span without intermediate mullion support, often requiring steel HSS tube reinforcement within the aluminum framing for spans exceeding 8 feet.
Florida Energy Conservation Code 7th Edition requires commercial fenestration in Climate Zone 1 (Broward County) to achieve maximum assembly U-factor of 0.50 and maximum SHGC of 0.25. Hurricane-rated storefronts face inherent conflicts because heavier aluminum framing increases thermal conductivity, impact-rated laminated glass with PVB or SGP interlayers adds weight requiring heavier framing, and thermal break integrity must survive cyclic pressure testing without delamination. Solutions include specifying high-performance low-E coatings on laminated assemblies, using thermally broken profiles with structural-grade polyamide breaks, and employing area-weighted averaging per ASHRAE 90.1 Section 5.5.4.2 where insulated spandrel panels offset higher-U storefront sections to achieve compliance on a wall-area basis rather than per-component.
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