What are Components and Cladding (C&C)?
Components and Cladding (C&C) refers to individual building envelope elements and their attachments to the primary structural system. Unlike the Main Wind Force Resisting System (MWFRS) which addresses overall building stability, C&C design focuses on localized pressures acting on specific building components and their fasteners.
C&C elements experience significantly higher wind pressures than MWFRS due to their smaller tributary areas and localized wind effects such as corner suction and edge pressures. These elements are the building's first line of defense against wind and weather, making proper C&C design critical for preventing water infiltration, air leakage, and localized damage.
ASCE 7 Definition: Components and Cladding
ASCE 7 defines Components and Cladding as "elements of the building envelope that do not qualify as part of the Main Wind Force Resisting System." This includes all exterior wall coverings, roofing materials, windows, doors, and their attachments that receive wind loads directly or from surfaces tributary to them.
Typical Components and Cladding Elements
Wall Components
- Windows: Fixed glass, operable windows, skylights, glazing systems
- Doors: Entry doors, garage doors, overhead doors, sliding glass doors
- Wall Panels: Metal panels, precast concrete panels, curtain walls, EIFS
- Siding: Vinyl siding, wood siding, fiber cement, brick veneer
- Cladding Fasteners: Screws, clips, anchors, bolts connecting panels to structure
Roof Components
- Roofing Materials: Shingles, tiles, metal roofing, membrane roofing, standing seam
- Roof Panels: Structural panels, deck panels, insulated metal panels
- Roof Fasteners: Nails, screws, clips, adhesives securing roofing to deck
- Roof-Mounted Equipment: HVAC units, solar panels, satellite dishes, signs
- Parapets: Parapet walls and coping systems
Other Components
- Canopies and Awnings: Entrance canopies, window awnings, sunshades
- Louvers and Vents: Roof vents, wall louvers, soffit vents
- Soffits and Overhangs: Eave soffits, fascia boards, overhangs
- Architectural Features: Decorative trim, cornices, signage, screening
C&C vs. MWFRS: Key Differences
Understanding the distinction between C&C and MWFRS is fundamental to proper wind load design:
C&C (Components & Cladding)
- Scope: Individual building envelope elements and fasteners
- Tributary Area: Small areas (typically < 700 sq ft)
- Pressure Magnitude: Higher due to localized wind effects
- Pressure Zones: Multiple zones with varying pressures (corners, edges, interior)
- Load Path: Element → fastener → supporting structure
- Failure Consequences: Localized damage, blown-off panels, broken glass, water infiltration
- Design Goal: Prevent envelope breach and component failure
MWFRS (Main Wind Force Resisting System)
- Scope: Primary structural system and overall building stability
- Tributary Area: Large areas (typically > 700 sq ft)
- Pressure Magnitude: Lower due to area averaging
- Pressure Zones: Windward, leeward, side walls, roof zones
- Load Path: Roof/wall → diaphragm → lateral system → foundation
- Failure Consequences: Structural collapse, building instability
- Design Goal: Ensure overall structural integrity and stability
Important Note: Both C&C and MWFRS Must Be Designed
Every building project requires BOTH C&C and MWFRS wind load calculations. Engineers must design the structural frame using MWFRS pressures AND design the building envelope using C&C pressures. These are separate, independent calculations with different methodologies and pressure magnitudes.
ASCE 7 Calculation Procedures for C&C
Part 1: Low-Rise Buildings (Mean Roof Height ≤ 60 ft)
ASCE 7 Chapter 30 Part 1 provides a simplified method for low-rise buildings using pressure coefficient tables. This is the most commonly used procedure for residential and light commercial construction.
Chapter 30 Part 1 Requirements
- Mean roof height ≤ 60 feet
- Regular-shaped building (rectangular, L-shaped, etc.)
- Flat terrain or with topographic multiplier applied
- Uses Figure 30.4-1 through 30.4-7 pressure coefficients
- Simplified zones: corner, edge, and interior regions
Part 2: Low-Rise Buildings - Alternate Procedure (Mean Roof Height ≤ 60 ft)
ASCE 7 Chapter 30 Part 2 provides an alternative approach for low-rise buildings with different pressure zones and coefficients. Results are similar to Part 1 but with different zone configurations.
Part 3: Buildings with Mean Roof Height > 60 ft
For taller buildings, ASCE 7 Chapter 30 Part 3 must be used. This method accounts for pressure variation with height and requires calculations at multiple elevations.
Part 4: Buildings with Mean Roof Height ≤ 160 ft
Chapter 30 Part 4 provides an additional simplified procedure for buildings up to 160 feet in height with specific geometry and exposure requirements.
C&C Design Pressure Formula
The basic C&C design pressure equation per ASCE 7 is:
C&C Design Pressure Formula
p = qh × [(GCp) - (GCpi)]
Where:
- p = Net design wind pressure (psf) - acting perpendicular to surface
- qh = Velocity pressure at mean roof height (psf)
- (GCp) = External pressure coefficient (from ASCE 7 figures/tables)
- (GCpi) = Internal pressure coefficient (±0.18 or ±0.55)
Note: The external and internal pressures are combined algebraically. For worst-case design, external suction (-) is combined with internal positive pressure (+), or external positive pressure is combined with internal suction.
Velocity Pressure at Mean Roof Height (qh)
The velocity pressure is calculated as:
qh = 0.00256 × Kh × Kzt × Kd × V²
- Kh = Velocity pressure exposure coefficient at mean roof height h
- Kzt = Topographic factor (1.0 for flat terrain)
- Kd = Wind directionality factor (0.85 for buildings)
- V = Basic wind speed (mph) from ASCE 7 wind speed maps
External Pressure Coefficients (GCp)
External pressure coefficients for C&C vary based on:
- Zone Location: Corner zones have highest suction, edge zones intermediate, interior zones lowest
- Effective Wind Area: Smaller areas experience higher pressures (size reduction factor)
- Building Geometry: Roof slope, wall height, building proportions
- Component Type: Positive pressures (inward) and negative pressures (suction/outward)
Typical C&C Pressure Zones (Low-Rise Buildings)
- Zone 1: Interior zone (lowest pressures)
- Zone 2: Edge zone along perimeter
- Zone 3: Corner zone (highest suction pressures)
- Zone 4: Roof ridge/hip (for sloped roofs)
- Zone 5: Roof overhang
Zone dimensions are typically defined as a function of building dimensions (e.g., edge zones extend 10% of building width or 40% of eave height from corners).
Effective Wind Area
Effective wind area is one of the most critical parameters in C&C design. It represents the area of the building surface contributing wind load to the component being designed, including tributary areas.
How to Determine Effective Wind Area
- For cladding fasteners: Area = fastener spacing × fastener spacing
- For single panels: Area = panel width × panel height
- For windows: Area = window width × window height
- For continuous elements: Area = span length × effective width
- For girts/purlins: Area = member span × tributary width
Effect of Area on Pressure Coefficients
ASCE 7 pressure coefficients vary with effective wind area. Smaller areas experience higher pressures due to peak suction effects:
- 10 sq ft: Highest (GCp) values - governs small fasteners and attachments
- 100 sq ft: Intermediate (GCp) values - typical for panels and windows
- 500 sq ft: Lower (GCp) values - large panels or multiple windows
This is why corner fasteners on metal roofing often require closer spacing than interior fasteners - they experience much higher suction.
Pressure Zones and Design Regions
Wall Zones
Building walls are divided into zones based on proximity to corners and edges:
- Corner Zones (Zone 5): Highest suction; extend from corners based on building dimensions
- Edge Zones (Zone 4): Moderate pressures; adjacent to corner zones
- Interior Zones (Zone 4 or 5): Lowest pressures; central wall areas
Roof Zones
Roof zoning depends on roof slope and configuration:
- Corner Zones: Highest roof suction at building corners
- Edge Zones: Perimeter zones along eaves and rakes
- Interior Zones: Central roof areas with lower pressures
- Ridge/Hip Zones: Special zones for sloped roofs at ridges and hips
Internal Pressure Coefficients (GCpi)
Internal pressure acts on the interior surfaces of the building envelope. The magnitude depends on the building enclosure classification:
Enclosed Buildings
GCpi = ±0.18
- Buildings with all openings protected or limited in size
- Most residential and commercial buildings
- Both positive and negative internal pressures must be considered
Partially Enclosed Buildings
GCpi = ±0.55
- Buildings with large openings in one wall (e.g., garage door open during storm)
- Significantly increases net design pressures
- Common for agricultural buildings, parking structures with open sides
- Must be considered if dominant opening could occur
Open Buildings
Buildings with no enclosed space use special provisions per ASCE 7 Section 26.4.
Design for Both Internal Pressure Coefficients
C&C elements must be designed for BOTH +GCpi and -GCpi to determine the worst-case net pressure:
- Outward pressure: External suction (-GCp) + Internal positive (+GCpi)
- Inward pressure: External positive (+GCp) + Internal suction (-GCpi)
The governing case is typically suction (negative external + positive internal), especially at corners and edges.
Common C&C Design Applications
Window and Door Design
Windows and doors must resist both positive (inward) and negative (outward) pressures:
- Design pressure determines required performance grade (PG rating)
- Corner windows require higher ratings than interior windows
- Large windows may require structural framing or intermediate mullions
- Impact-resistant glazing required in HVHZ and coastal high-wind zones
- Anchor spacing and fastener selection based on C&C pressures
Metal Roof Panel Design
Standing seam and through-fastened metal roofing requires detailed C&C analysis:
- Panel Selection: Panel gauge and profile based on span and design pressure
- Clip Spacing: Closer spacing at corners and edges where suction is highest
- Fastener Selection: Through-fastened systems require appropriate screw size and spacing
- Effective Wind Area: Calculated for individual fasteners and panel spans
- Zone-Specific Design: Different fastener patterns for corner, edge, and field zones
Wall Cladding Systems
Exterior wall panels and cladding attachments:
- Pressure equalized rainscreen systems reduce net pressures
- Fastener load capacity must exceed C&C design loads with safety factor
- Panel deflection limits prevent glass breakage and seal failure
- Corner and edge zones may require supplemental framing or closer spacing
Special Considerations for C&C Design
Roof Overhangs and Soffits
Roof overhangs experience combined upper and lower surface pressures that can be substantial. ASCE 7 provides specific (GCp) values for overhang surfaces that account for simultaneous pressures on top and bottom surfaces.
Parapets
Parapets are subject to wind from both sides and require special pressure coefficients. Parapet height significantly affects design pressures, with taller parapets experiencing higher loads.
Roof-Mounted Equipment
HVAC units, solar panels, and other rooftop equipment must be designed as C&C elements. Equipment location (corner, edge, or interior) affects design pressures. Attachment points require careful design for uplift and overturning.
Canopies and Awnings
Free-standing canopies and building-attached awnings experience unique wind loading. Both upper and lower surface pressures act simultaneously, often producing significant net uplift. Attachment to building or support structure is critical.
Testing and Product Approval
Performance Testing Standards
Many C&C products require testing to verify wind resistance:
- Windows and Doors: ASTM E330 (structural testing), AAMA standards
- Roof Assemblies: FM 4470, UL 580, UL 1897 wind uplift testing
- Wall Cladding: ASTM E330, manufacturer specific testing
- Impact Resistance: ASTM E1996, ASTM E1886 (large missile), Florida Building Code TAS protocols
Product Approval in High-Wind Zones
Florida HVHZ and other high-wind jurisdictions require:
- Florida Product Approval: Notice of Acceptance (NOA) from Miami-Dade or Florida Building Commission
- Testing: Products must pass wind pressure, wind-driven rain, and large missile impact tests
- Quality Assurance: Special inspection requirements during installation
- Installation Instructions: Must follow manufacturer's approved installation details exactly
C&C Calculation Software
Due to the complexity of C&C calculations with multiple zones, varying effective wind areas, and numerous building elements, professional wind load calculator software is essential for accurate and efficient design:
- Automatic zone determination based on building geometry
- Pressure coefficients from ASCE 7 figures/tables for any effective wind area
- Both enclosed and partially enclosed internal pressure calculations
- Zone-specific design pressures for corners, edges, and interior
- Detailed pressure diagrams showing zone boundaries
- Calculation reports suitable for permit submittal and product specification
Why Manual C&C Calculations are Error-Prone
- Multiple pressure zones require separate calculations for each component
- Interpolation of (GCp) values between table/figure areas is complex
- Easy to miss worst-case load combinations (internal pressure sign)
- Effective wind area determination requires careful attention
- Different procedures for different building heights add complexity
Best Practices for C&C Design
- Always calculate both MWFRS and C&C: Both are required and serve different purposes
- Identify all pressure zones: Use ASCE 7 figures to properly define corner, edge, and interior zones
- Calculate effective wind area correctly: Tributary area including attachments, not just component size
- Check both positive and negative pressures: Both inward and outward loading cases
- Consider internal pressure: Include both +GCpi and -GCpi in calculations
- Use appropriate procedure: Chapter 30 Part 1, 2, 3, or 4 based on building height and geometry
- Account for topographic effects: Hills and escarpments increase pressures significantly
- Verify product ratings: Ensure windows, doors, and roofing meet required design pressures
- Detail connections properly: Fastener size, spacing, and edge distances per manufacturer requirements
- Consider construction sequencing: Partially complete buildings may be more vulnerable
Conclusion
Components and Cladding design is critical for building envelope performance and weather resistance. C&C pressures are typically higher than MWFRS pressures due to smaller tributary areas and localized wind effects, making proper analysis essential to prevent costly failures, water damage, and building envelope breaches.
Understanding ASCE 7 C&C procedures, pressure zones, effective wind areas, and internal pressures enables engineers and designers to specify appropriate products and fastening systems. Professional wind load calculator software automates these complex calculations while ensuring accuracy and code compliance across all zones and building geometries.