A skylight is one of the most vulnerable components in your roof assembly. In Broward County, where design wind speeds reach 170-180 MPH, an unprotected or improperly rated skylight becomes a direct path for pressurization that can tear a roof apart from the inside. Understanding flat vs domed performance, curb vs deck mounting, large missile impact certification, and FBC product approval is what separates a compliant installation from a catastrophic failure chain.
When a skylight fails during a hurricane, the financial damage compounds exponentially. Each phase of failure triggers the next, turning a single glazing breach into a six-figure insurance claim.
The skylight itself costs only $2,400 to replace. But once the envelope breaches, water infiltration and internal pressurization drive damage 24 times beyond the original component cost. Investing $800 more in a properly impact-rated skylight eliminates the entire cascade.
Profile geometry determines how wind interacts with a skylight. The choice between flat and domed is not merely aesthetic — it has measurable structural implications in Broward's high-wind environment.
Flat skylights sit flush with the roof plane, presenting a surface that wind flows across abruptly. The sharp edges create flow separation, generating intense suction peaks at the windward and leeward edges. In ASCE 7-22 terminology, flat skylights experience Component and Cladding (C&C) pressures at full intensity because wind cannot transition smoothly across the surface.
The GCp coefficient for flat roof-mounted glazing ranges from -1.8 to -2.8 depending on tributary area and zone location. At roof corners (Zone 3), where wind accelerates around building edges, flat skylights encounter the most severe uplift. A 4 ft by 4 ft flat skylight in a corner zone on a 30-foot building in Broward can see net uplift pressures exceeding -65 psf — requiring DP-65 minimum rating.
Flat skylights also face perpendicular debris impacts. Wind-borne missiles strike the glazing surface at 90 degrees, concentrating maximum kinetic energy at the impact point. This is the worst-case scenario for impact resistance testing.
Domed profiles force wind to follow a curved path, reducing flow separation and lowering peak suction coefficients by 15-25% compared to flat glazing at the same roof location. The dome shape distributes wind pressure across a three-dimensional surface rather than a flat plane, reducing stress concentration at edges.
The optimal dome rise-to-span ratio of 1:4 to 1:3 provides the best balance. Too flat and you lose the aerodynamic benefit. Too tall and the dome creates additional drag and projected area that increases total wind force. Most impact-rated domed skylights use acrylic or polycarbonate outer layers that are inherently more impact-resistant than monolithic glass.
Wind-borne debris strikes domed surfaces at oblique angles, deflecting some of the kinetic energy laterally instead of absorbing it all at the impact point. This geometric advantage allows domed skylights to pass large missile impact testing with thinner glazing layers in some configurations.
Skylights sit at the highest point of the building envelope. When one fails, wind enters the attic or interior space and transforms your roof from a shelter into a sail.
ASCE 7-22 classifies buildings as "enclosed" or "partially enclosed" based on envelope openings. An intact building uses GCpi = +0.18 / -0.18 for internal pressure. When a skylight breaches, the building shifts to partially enclosed with GCpi = +0.55 / -0.55 — tripling the internal pressure coefficient. This dramatically increases net uplift on every roof panel, truss connection, and fastener across the entire roof area, not just near the failed skylight.
A skylight breach is worse than a window breach for internal pressurization because of its location. Wind entering at the roof level pressurizes the attic space directly against the roof deck — the exact surface that is simultaneously experiencing maximum external uplift suction. The combined effect of external suction plus internal pressure can exceed the roof-to-wall connection capacity by 40-60%, initiating progressive roof failure that cascades across the entire structure.
Hurricane-force rain driven through a breached skylight at 100+ MPH deposits 2-4 gallons per minute into the building interior. This water saturates ceiling insulation (adding dead load to the roof structure), degrades drywall and wood framing, causes electrical system failures, and promotes mold growth within 24-48 hours. The structural weakening from water saturation reduces the capacity of wood trusses and connections to resist the next wind gust.
Broward County enforces wind-borne debris protection requirements throughout the county per FBC Section 1609.1.4. All glazed openings — including skylights — within the wind-borne debris region must be protected with impact-resistant glazing or approved shuttering systems. Skylights present a unique challenge because rooftop shutter systems are impractical, making impact-rated glazing the only viable compliance path for most skylight installations.
Before a skylight can be installed in Broward County's wind-borne debris region, it must survive one of the most demanding impact tests in the building products industry.
The large missile impact test fires a 9-pound section of 2x4 lumber at the skylight glazing at 50 feet per second (34 MPH). The projectile is accelerated by a pneumatic cannon and strikes the skylight at a specified point — typically center of the largest glazing panel and near a corner. After surviving the impact without penetration, the skylight must then pass a cyclic pressure loading test simulating 8,500 positive and negative wind pressure cycles at the design wind pressure. This combined impact-plus-cycling sequence ensures the skylight can take a hit from flying debris and continue resisting wind loads for the remainder of the storm. Products that crack but do not allow penetration through the full glazing assembly can still pass — the standard measures breach prevention, not cosmetic integrity.
The skylight assembly is mounted in a test frame that replicates actual installation conditions — including the curb or deck mounting hardware. Temperature conditioning ensures the glazing is tested at realistic conditions, not ideal laboratory temperatures that might artificially improve impact resistance.
Two separate impacts are delivered: one at the center of the largest glazing area and one within 2 inches of a corner or edge. The corner impact is typically the critical test because glass and laminate layers are less supported near frame intersections. Both impacts must result in no through-penetration of the complete glazing system.
After impact, the skylight is subjected to 4,500 positive pressure cycles and 4,000 negative pressure cycles at the rated design pressure. The positive cycles simulate wind gusts pushing against the damaged glazing; negative cycles simulate suction pulling the impacted panel outward. No failure of the glazing retention or frame is permitted during cycling.
Products that survive both impact and cycling receive a test report that documents the maximum design pressure achieved. This report becomes the basis for Florida Building Code product approval. The product approval specifies the exact skylight model, glazing configuration, frame type, and mounting method — changing any component requires retesting.
The mounting method determines how wind forces transfer from the skylight frame into the roof structure. Each approach carries distinct engineering trade-offs for hurricane resistance.
| Characteristic | Curb-Mounted | Deck-Mounted |
|---|---|---|
| Profile Height | 4-8 inches above roof plane | Flush with roof surface |
| Wind Exposure | Higher — increased projected area | Lower — reduced by 10-20% |
| Structural Connection | Continuous wood/metal curb bolted to framing | Flange brackets screwed to deck sheathing |
| Uplift Resistance Path | Direct to roof rafters/trusses via curb | Through deck sheathing to framing — requires blocking |
| Typical DP Requirement | 10-20% higher than deck-mounted at same location | Lower DP needed for same roof zone |
| Water Management | Curb height provides natural drainage dam | Relies on counter-flashing and sealant integrity |
| Replacement Ease | Skylight lifts off curb — curb stays | Full removal required including flashing |
| Code Prevalence in Broward | Standard for commercial and retrofit residential | Common for new residential construction |
For hurricane-prone areas, curb-mounted skylights generally provide superior wind resistance due to the direct structural load path from the curb frame through continuous fastening into roof rafters or trusses. The curb acts as a built-up beam that distributes uplift forces across multiple fastening points. While deck-mounted skylights offer lower wind exposure, their reliance on sheathing connections creates a weaker link in the load chain. When a deck-mounted skylight is specified, structural blocking between rafters beneath the mounting flanges is essential to prevent pull-through failure of the deck fasteners under design wind uplift.
Wind rating is only one piece of the skylight specification puzzle. Condensation resistance and thermal performance interact with wind design in ways that affect long-term durability.
As skylight size increases, the tributary area for wind pressure grows, requiring higher total wind force resistance. A 2x4 ft skylight in a roof corner zone might need DP -50, while a 4x6 ft skylight at the same location could require DP -45 per square foot but must resist 3x the total force. Most impact-rated skylights max out around 4x8 ft for a single unit. Larger openings need multiple units with structural mullions engineered for wind load transfer.
Broward's subtropical humidity (average 75% RH) makes condensation management critical. Skylights with low CRF ratings develop interior condensation that corrodes frame hardware, degrades sealants, and weakens laminated glazing interlayers over time. A skylight that passes impact testing when new may fail after 5-7 years if condensation has compromised its structural integrity. Specify CRF ratings of 50 or higher for Broward installations.
Florida Energy Code requires skylights to meet U-factor maximums (currently 0.75 for residential). Impact-rated skylights use laminated glass with PVB or SGP interlayers that inherently improve thermal performance. Low-E coatings reduce solar heat gain coefficient (SHGC) to 0.25 or below, cutting cooling loads. The thicker glazing assemblies required for impact rating — typically 9/16 to 3/4 inch total — also improve thermal insulation compared to standard single-pane skylights.
TDDs (sun tunnels) are a skylight alternative with inherent wind advantages. Their small diameter — 10 to 21 inches — produces low total wind forces even at high pressures. The acrylic or polycarbonate dome on most TDDs provides natural impact resistance. Impact-rated TDDs typically achieve DP -40 to -55 easily, and their small roof penetration minimizes the pressurization risk if a failure did occur. Most major TDD manufacturers offer FBC-approved impact-rated models.
Fixed skylights outperform operable units for wind resistance because the glazing panel is continuously supported on all four sides. Operable skylights introduce hinges, latches, and weatherstrip seals that create structural discontinuities. Most impact-rated operable skylights carry DP ratings 15-25% lower than equivalent fixed units at the same size. Broward code requires operable skylights to meet full DP requirements in the closed and locked position.
Every skylight installed in Broward County must hold a valid Florida Building Code product approval. The approval document specifies the exact model, glazing makeup, frame material, maximum size, and approved mounting methods. Product approvals are searchable at the FL DBPR product approval site. Using a skylight without valid FBC approval — even if it has ASTM test reports — will not pass Broward County building inspection and will require removal and replacement.
Skylight installations in Broward require building permits with specific documentation that demonstrates code compliance for wind loads, impact resistance, and energy performance.
A skylight permit application in Broward County requires a signed and sealed wind load calculation showing the design pressure at the specific roof location where the skylight will be installed. The calculation must follow ASCE 7-22 methodology and account for building height, exposure category, roof slope, and the skylight's zone position (field, edge, or corner).
The FBC product approval number must be listed on the permit application, and the approved product's DP rating must meet or exceed the calculated design pressure. If the skylight is in a wind-borne debris region (most of Broward), the product approval must include large missile impact certification per TAS 201/203 or ASTM E1886/E1996.
For curb-mounted installations, a detail drawing showing the curb construction, fastener schedule, and flashing system is typically required. Deck-mounted installations require documentation of structural blocking beneath the mounting points. Energy code compliance documentation showing U-factor and SHGC values must also be included.
Verifies roof framing, headers, blocking, and curb construction match the approved plans before the skylight is set.
Inspector confirms step flashing, counter flashing, and sealant details comply with manufacturer installation instructions and the FBC.
Installed skylight model, size, and glazing are verified against the FBC product approval. Labels must be visible and match the permit documents.
Answers to the most common questions about impact-rated skylight requirements in Broward County.
Skylights in Broward County must meet the Florida Building Code design wind speed of 170-180 MPH depending on location within the county. The required design pressure (DP) rating depends on skylight size, roof slope, building height, and position on the roof. Corner and edge zones require higher DP ratings than field-of-roof locations. Typical residential skylights need DP ratings from -40 to -65 psf for uplift, with higher values required near roof edges and corners.
Yes. In Broward County's HVHZ areas and wind-borne debris regions (within one mile of the coast or in areas with design wind speeds of 130 MPH or greater), skylights must pass large missile impact testing per ASTM E1886/E1996 or TAS 201/203. This involves a 9-pound 2x4 lumber projectile fired at 50 feet per second at the glazing. The skylight must resist penetration and maintain structural integrity after impact, then pass a subsequent cyclic pressure test.
A skylight failure during a hurricane creates a breach in the building envelope that allows wind to pressurize the interior. Internal pressurization can increase roof uplift forces by 50-80% compared to an enclosed building. This cascading failure often leads to roof deck separation, soffit blowout, additional envelope breaches, and potentially total roof loss. A single 2x4 ft skylight breach can generate enough internal pressure to lift roof sections across the entire structure. This is why code treats skylights as critical wind-borne debris protection components.
Domed skylights generally perform better aerodynamically than flat skylights in hurricane conditions. The curved profile reduces suction coefficients by 15-25% compared to flat glazing at the same roof location. Domed shapes deflect wind-borne debris more effectively because impacts occur at oblique angles rather than perpendicular strikes. However, domed skylights must still carry impact certification and meet the same DP rating requirements. The dome rise-to-span ratio affects performance — a ratio of 1:4 to 1:3 provides optimal wind deflection without creating excessive drag.
Curb-mounted skylights sit on a raised frame (curb) built on the roof deck, while deck-mounted skylights attach directly flush with the roof surface. Curb-mounted units have a taller profile that increases wind exposure and typically requires higher DP ratings to account for the additional projected area. However, curb mounting provides a more robust mechanical connection to the roof structure through continuous anchoring around the curb perimeter. Deck-mounted skylights present a lower profile, reducing wind loads by 10-20%, but rely on flashing and sealant connections that must be carefully detailed to prevent water intrusion under wind-driven rain.
While there is no absolute size cap for skylights in Broward's HVHZ, practical limitations arise from product availability and engineering constraints. Most impact-rated skylights max out at approximately 4 ft x 8 ft for a single glazed unit. Larger openings require multiple skylight units with structural mullions or continuous ridge skylights with engineered framing. The required DP rating increases with skylight size because wind pressure on larger glazing areas generates greater total force. Skylights exceeding 16 square feet in HVHZ areas often require structural engineering review and custom product approvals.
Yes, tubular daylighting devices (TDDs) are roof penetrations and must meet the same wind load and impact requirements as skylights. The rooftop dome of a TDD must be impact-rated for wind-borne debris regions, and the entire assembly must have a DP rating meeting the calculated wind pressure at its roof location. Most TDD manufacturers offer impact-rated models with FBC product approval. The advantage of TDDs is their small diameter — typically 10 to 21 inches — which results in lower total wind loads compared to traditional skylights, often requiring DP ratings of only -30 to -45 psf.
Operable skylights can be installed in Broward County but must meet the same wind load and impact requirements as fixed skylights when in the closed position. The hinge mechanism, locking hardware, and weatherstripping must be rated for the full design wind pressure. Operable skylights typically carry DP ratings 15-25% lower than equivalent fixed units because the hinge and seal reduce structural continuity. Many impact-rated operable skylights are limited to smaller sizes — typically 24 x 48 inches maximum. During a hurricane warning, operable skylights must be closed and locked to function as rated envelope protection.
Calculate the exact design pressure your skylight needs based on building height, roof zone, and Broward County wind speed requirements.
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