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Broward County PEMB Secondary Framing

Wall Girt Spacing & Wind Pressure Distribution

Wall girt design is where most pre-engineered metal building failures originate during hurricanes. In Broward County at 170 MPH design wind speed, wall suction pressures in corner zones can exceed 50 psf on secondary framing. Girt spacing, profile selection, and connection type determine whether your wall cladding stays attached or becomes wind-borne debris.

Calculate Wall Girt Loads View Pressure Distribution

Corner Zones Destroy Undersized Girts

ASCE 7-22 wall Zone 5 (corners) produces GCp values 40-50% higher than Zone 4 (field). A girt spacing that works in the middle of the wall can fail catastrophically at corners. Every PEMB wall must be designed with zone-specific pressures and independently verified girt capacity at each spacing.

0 MPH Design Wind Speed
L/120 Deflection Limit
C & Z Girt Profiles
0 psf Peak Corner Suction

Wall Girt Pressure Distribution

Side elevation showing wind pressure loading across girt spans. Adjust spacing to see how tributary area affects stress and deflection.

Low Stress
High Stress
Wind Pressure
Girt Members
4'-0" | Tributary Load: 26.8 psf

C-Girt vs. Z-Girt: Choosing the Right Profile

Both cold-formed steel profiles resist wall wind loads, but their behavior differs under Broward County hurricane pressures

C-Girt (Channel)
Symmetric cross-section

C-girts have a symmetric channel shape with equal flanges. Under wind pressure, the load passes directly through the shear center, producing pure bending without twist. However, C-girts cannot be lapped at column supports, limiting them to simple-span behavior that reduces moment capacity.

  • Simple-span only between columns
  • No biaxial bending correction needed
  • Common sizes: 6C054, 8C054, 8C068, 10C075
  • Ideal for spans under 20 feet
  • Easier connection detailing at columns
  • Cannot nest for shipping efficiency
Z-Girt (Zee)
Asymmetric cross-section

Z-girts are the industry standard for pre-engineered metal buildings in hurricane zones. Their asymmetric shape allows lapping at column supports, creating semi-continuous spans that increase negative moment capacity by approximately 30%. This additional capacity is critical for Broward County's 170 MPH wind loads on long spans.

  • Lapped at columns for continuity
  • 30% higher moment capacity than simple-span
  • Common sizes: 8Z060, 8Z075, 10Z060, 10Z075
  • Biaxial bending must be designed for
  • Nest together for lower shipping cost
  • Standard for PEMB wall systems

Girt Spacing Guidelines for 170 MPH Wind Speed

Typical maximum spacings for Broward County non-HVHZ zones. Reduce spacing 10-15% for HVHZ (180 MPH) areas.

Girt Size Wall Zone 4 (Field) Wall Zone 5 (Corner) Max Span Deflection Control
6Z060 3'-6" 2'-6" 20 ft L/120 governs above 16 ft span
8Z060 4'-6" 3'-0" 25 ft L/120 governs above 20 ft span
8Z075 5'-0" 3'-6" 27 ft Strength may govern for short spans
10Z060 5'-6" 4'-0" 30 ft Best balance of strength and stiffness
10Z075 6'-0" 4'-6" 32 ft Strength governs for most spans
Design Note: All spacings assume lapped Z-girt connections providing semi-continuous behavior, Exposure C, Risk Category II, and standard metal panel cladding. Corner zone width per ASCE 7-22 is the lesser of 10% of the least horizontal dimension or 0.4 times the mean roof height. Actual spacings require calculation by a Florida-licensed PE using project-specific parameters.

Bypass vs. Flush Girt Connections

Connection type affects both wind load path and cladding continuity on Broward County PEMB projects

Bypass Connection (Outboard Mount)

The girt mounts on the outside face of the column flange, bypassing the column entirely. This is the standard connection for pre-engineered metal building wall systems because the exterior cladding runs continuously past the column without interruption.

In Broward County, bypass connections must resist the full tributary wind pressure load on the girt plus the eccentricity moment from the offset between the girt web and the column flange centerline. This offset is typically 2-4 inches and adds 15-20% to the bolt shear demand.

  • Cladding is continuous past columns
  • Simpler erection sequence
  • Eccentricity adds bolt demand (15-20%)
  • Standard 2-bolt clip angle connection
  • Allows girt lapping at column face
  • Preferred for 90% of PEMB wall systems

Flush Connection (Inboard Mount)

The girt sits between column flanges, creating a flush exterior plane. This configuration eliminates the eccentricity problem but requires cladding to span across column flanges or use column closure trim pieces, adding material and labor cost.

Flush connections transfer wind load directly through the girt web to the column web via clip angles or seat brackets. While structurally simpler, the lack of cladding continuity creates potential weatherproofing challenges at every column location in Broward County's wind-driven rain environment.

  • No eccentricity in connection
  • Flush exterior wall plane
  • Cladding interrupted at every column
  • More trim and sealant needed
  • Limits girt depth to column flange width
  • Used for aesthetic or insulation reasons

Wall Girt Deflection Limits

Deflection criteria often control girt sizing in Broward County rather than bending stress

L/120
Standard Metal Panels

The minimum deflection limit for wall girts supporting through-fastened or standing seam metal cladding per AISI S100 and IBC Table 1604.3.

25 ft span: 2.50" max
30 ft span: 3.00" max
L/150
Insulated Metal Panels

Used when insulated metal panels (IMP) or foam-core panels are specified. Panel manufacturers often require tighter limits to prevent joint separation.

25 ft span: 2.00" max
30 ft span: 2.40" max
L/180
Brittle Finishes / Masonry Veneer

Required when girts support EIFS, stucco, thin-brick veneer, or other brittle cladding systems. Cracking occurs at lower deflections.

25 ft span: 1.67" max
30 ft span: 2.00" max
Why Deflection Controls in Broward County: At 170 MPH design wind speed, girt bending stress may be within allowable limits while deflection exceeds L/120. A 10Z060 girt at 5' spacing spanning 28' may have only 85% stress ratio but 110% deflection ratio. Upgrading to 10Z075 solves the deflection issue. Always check both criteria. Deflection is calculated using service-level wind loads (unfactored), not strength-level loads.

Cladding Attachment to Wall Girts

Fastener pattern design determines whether wall panels stay attached under Broward County hurricane suction pressures

Through-Fastened Metal Panel Systems

Through-fastened wall panels connect directly to girt flanges using self-drilling screws. Each screw resists wind suction through two failure modes: pull-out from the girt flange (screw thread withdrawal) and pull-over through the panel (head punching through the sheet). The lower of these two capacities governs the fastener spacing design.

In Broward County, negative (suction) pressures on walls range from -22 psf in field zones to -52 psf in corner zones at 170 MPH (Risk Category II, Exposure C, enclosed building). These pressures attempt to pull the cladding off the girts. The fastener pattern must resist these pressures with a safety factor per AISI S100.

For typical 26-gauge ribbed metal panels on 16-gauge girts, a single #12 TEK screw provides approximately 150-200 lbs pull-out and 300-400 lbs pull-over capacity. At -52 psf corner pressure with 12-inch fastener tributary width, each screw resists 52 psf x 1.0 ft = 52 plf. A single screw per rib at 12" spacing provides 150/52 = 2.88 safety factor, which is adequate. But at 24" spacing, the safety factor drops to 1.44, which fails the required 1.67 ASD factor per AISI.

Standing Seam Wall Panels

Standing seam wall panels use concealed clips similar to roof systems. Clip capacity must be verified against the same zone-specific suction pressures. Standing seam systems provide better weatherproofing but have lower pull-off resistance than through-fastened panels, requiring closer clip spacing in Broward County corner zones.

Fastener Spacing by Wall Zone

Zone 4 - Field
12"
Standard spacing
-22 to -28 psf
Zone 4 - Near Openings
9"
Enhanced spacing
-28 to -35 psf
Zone 5 - Corner Edge
8"
Reduced spacing
-35 to -45 psf
Zone 5 - Corner Peak
6"
Maximum density
-45 to -52 psf
Critical: Fastener spacing shown is for #12 TEK screws into 16-gauge minimum girt flanges with 26-gauge panels. Thinner girts or panels require closer spacing. Verify per AISI S100 Section J6.

Tributary Area and Effective Wind Area

Understanding ASCE 7-22's effective wind area provision saves material cost on every girt in the building

Tributary area for a wall girt is calculated as the girt spacing multiplied by the girt span length. A girt at 5'-0" spacing spanning 25 feet has a simple tributary area of 125 square feet. However, ASCE 7-22 defines effective wind area as the larger of (a) the span times tributary width, or (b) the span squared divided by three (L2/3).

For the same 25-foot span girt: L2/3 = 625/3 = 208 sq ft, which exceeds the 125 sq ft simple tributary area. This larger effective area reduces the GCp coefficient used in pressure calculations, resulting in lower design pressures and potentially allowing wider girt spacing or lighter gauge steel.

This provision recognizes that long, narrow tributary areas experience spatial averaging of wind pressure fluctuations. The peak pressure that hits one portion of the girt span does not occur simultaneously across the entire span. Designers who miss this provision overdesign wall girts by 10-20%, adding unnecessary steel weight and cost to every bay of a Broward County metal building.

Girt Span Spacing Simple Trib. Effective Area Governs
20 ft 5'-0" 100 sq ft 133 sq ft L2/3
25 ft 5'-0" 125 sq ft 208 sq ft L2/3
25 ft 4'-0" 100 sq ft 208 sq ft L2/3
30 ft 5'-0" 150 sq ft 300 sq ft L2/3
30 ft 5'-0" 150 sq ft 300 sq ft L2/3
Key Insight: For typical PEMB girt spans (20-30 ft), the L2/3 rule almost always governs effective wind area. Only at very close girt spacings combined with short spans does the simple tributary area control.

Wall Girt Design FAQs

Common questions about wall girt spacing and wind loads for pre-engineered metal buildings in Broward County

What is the maximum wall girt spacing for a pre-engineered metal building in Broward County?
Maximum wall girt spacing in Broward County depends on the design wind speed (170 MPH for non-HVHZ, 180 MPH for HVHZ), wall zone location per ASCE 7-22, girt profile depth and gauge, and the cladding panel span rating. In wall field zones (Zone 4), typical maximum spacings range from 4'-0" using 8" deep girts to 6'-0" using 10" deep girts. Corner zones (Zone 5) require reduced spacing, often 3'-0" to 4'-6" depending on girt capacity. These spacings assume lapped Z-girt connections providing semi-continuous behavior, Exposure C, and Risk Category II. Each spacing must be verified by calculating the tributary area wind pressure against both the girt bending capacity per AISI S100 and the L/120 deflection limit.
What is the difference between C-girts and Z-girts for metal building walls?
C-girts have a symmetric channel cross-section, while Z-girts have an asymmetric Z-shaped cross-section. The critical difference for wind design is that Z-girts can be lapped at column supports, creating semi-continuous spans that increase moment capacity by approximately 30% compared to simple-span C-girts. Z-girts also nest together for efficient shipping. However, Z-girts produce biaxial bending under lateral wind pressure because the load does not pass through the shear center of the asymmetric section. AISI S100 Section C3.1.4 provides methods to account for this effect. In Broward County's 170 MPH wind zone, Z-girts with lapped connections are preferred for spans over 20 feet because the additional continuity capacity outweighs the biaxial bending penalty.
What is the difference between bypass and flush girt connections?
Bypass connections mount the girt on the outboard face of the column flange, allowing cladding panels to run continuously past columns without interruption. Flush connections position the girt between column flanges, creating a flush exterior plane but requiring cladding to be interrupted at every column. Bypass connections are the industry standard for PEMB wall systems because they simplify erection and cladding installation. The trade-off is an eccentricity moment: the girt centerline is offset from the column flange by 2-4 inches, which adds approximately 15-20% to connection bolt demands. In Broward County, bypass connections must be designed for the full tributary wind load plus this eccentricity using a standard clip angle with two bolts minimum. The eccentric moment is often the controlling load case for connection design.
What deflection limit applies to wall girts under wind load in Florida?
The Florida Building Code adopts IBC Table 1604.3, which requires L/120 deflection limit for wall girts supporting flexible finishes like metal panels. This means a 25-foot span girt can deflect no more than 2.5 inches under service-level (unfactored) wind load. More stringent limits may apply: L/150 for insulated metal panels per manufacturer requirements, and L/180 for girts supporting brittle cladding like EIFS or stucco. In Broward County at 170 MPH, deflection frequently controls girt sizing for spans exceeding 20 feet. A girt that passes the bending stress check may still fail the deflection check, requiring either a deeper section (increasing moment of inertia) or a heavier gauge (marginally increasing stiffness). Always calculate both strength and serviceability before finalizing girt selection.
How does tributary area affect wall girt wind pressure per ASCE 7-22?
Tributary area directly determines the GCp coefficient in ASCE 7-22 C&C wall pressure calculations. The effective wind area equals the span times tributary width, but ASCE 7-22 specifies it cannot be less than the span squared divided by three (L^2/3). For typical PEMB girt spans of 20-30 feet, the L^2/3 rule almost always produces a larger effective area than the simple span-times-spacing calculation. Larger effective areas correspond to lower GCp values on the ASCE 7-22 wall C&C pressure charts (Figures 30.3-1 through 30.3-7), which reduces the design pressure applied to each girt. For example, moving from 100 sq ft to 200 sq ft effective area can reduce the Zone 5 corner GCp from approximately -1.4 to -1.2, saving 14% on wall girt design loads. Designers who overlook this provision systematically overdesign every wall girt in the building.
How do you attach metal wall cladding to girts in hurricane zones?
Metal wall cladding attaches to girts using self-drilling screws for through-fastened panels or concealed clips for standing seam systems. For through-fastened panels in Broward County, #12 or #14 diameter screws with neoprene-backed EPDM washers are standard. Screw spacing varies by wall zone: 12" in field zones where suction is -22 to -28 psf, reducing to 6-8" in corner zones where suction reaches -45 to -52 psf. Each fastener must be checked for pull-out from the girt flange (thread engagement into minimum 16-gauge steel) and pull-over through the panel (washer bearing on 26-gauge minimum panel). Per AISI S100 Section J6, the required safety factor is 1.67 for ASD. Standing seam wall clips provide cleaner aesthetics but typically have 30-40% lower pull-off capacity per clip compared to through-fastened screws, requiring closer clip spacing in Broward County's high-wind environment.

Calculate Your Wall Girt Wind Loads

Get zone-specific C&C pressures for wall girt design in Broward County. Our MWFRS calculator provides the wind load data your girt design requires.

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