Thank you to everyone who attended our "Basics of Boardwalk Design" webinar. Your participation and engagement was was greatly appreciated!
In case you missed it, here is the webinar recording from May 7, 2025.
You can browse the topics discussed and main takeaways using the sections and time stamps below (see detailed key takeaways at the bottom):
- 00:00 - Introduction and Objectives
- 02:00 - Boardwalk Location Planning
- 05:00 - Width and Clearance Considerations
- 09:00 - Material Options
- 14:00 - Design Codes and Vertical Loads
- 19:00 - Lateral Loads and Load Combinations
- 24:00 - Material Design and Specifications
- 28:00 - Foundation Selection Overview
- 31:00 - Foundation Types
- 37:00 - Railings and Add-ons
- 41:00 - Construction Methods
- 44:00 - Material Properties Comparison
- 48:00 - Case Studies and Applications
- 53:00 - Question & Answer Session
- Our resource on top-down construction and how to build a boardwalk over wetlands here (includes video from presentation).
- Our 'Basics of Boardwalk Design' webinar presentation
Basics of Boardwalk Design - Detailed Key Takeaways
[00:02:00 - 00:05:00] Boardwalk Location Planning
- Cost Awareness: Boardwalks are typically the most expensive components of trails/greenways
- Placement Strategy: Minimize boardwalk length where possible for cost efficiency
- Regulatory Considerations:
- EPA and Corps of Engineers regulate wetland areas
- Clean Water Act Section 404 provides permitting guidelines
- Regulations discourage placing fill in wetlands, necessitating elevated trails
- Environmental Impact Considerations:
- Shadowing effect of boardwalks
- Footprint of piles/foundations
- Pile diameter and spacing (both horizontal and longitudinal)
- Planning Approach: Identify delineated wetland areas for boardwalk placement
[00:05:00 - 00:09:00] Width and Clearance Considerations
- Vertical & Horizontal Clearances:
- Account for obstructions like signs or trees
- Bridge clearances (minimum 8 feet for cyclists)
- Consider emergency vehicle access requirements
- Factor in construction material delivery requirements
- Common Trail Widths:
- Most common: 10-12 feet wide
- Recent trend: 14-16 feet for larger applications
- Clear Width Definition:
- Distance measured between obstructions (handrails, grab rails, etc.)
- Actual boardwalk width may be wider to accommodate railings (add ~15 inches)
- Design Best Practice: Maintain consistent width between trail and boardwalk (avoid narrowing at bridges)
[00:09:00 - 00:14:00] Material Options
- Concrete Boardwalk Systems:
- Components: precast abutments, piers, stringers/beams, treads
- Advantages:
- Allows prefabrication during foundation installation (time-efficient)
- Enables longer spans (20-50 feet vs. 10-12 feet for timber)
- Reduces wetland impact due to fewer foundations required
- Structure: Longitudinal beams supported by piers with perpendicular treads on top
- Timber Boardwalk Systems:
- Traditional, widely-used approach with established methodology
- Components: timber piles, cross-bracing, headers, stringers, treads, railings
- Limitations: Typically limited to 10-12 foot spans
- Advantages:
- Often inexpensive
- Parts readily available (e.g., from home improvement stores)
- Many contractors familiar with construction method
- Composite Boardwalk Systems:
- Relatively newer option (~20 years on market)
- Fiberglass-type systems for piles, stringers, headers
- Often combined with timber substructures
- Examples: Wagner materials, TRX products
- Alternative: Metal grating systems for reducing shadowing on wetlands
[00:14:00 - 00:19:00] Design Codes and Vertical Loads
- Design Code Challenges:
- No dedicated boardwalk design code exists
- Boardwalks typically considered pedestrian bridges for design purposes
- Primary design guides:
- LRFD Bridge Design Specifications (for highway/vehicular bridges)
- LRFD Guide Spec for Design of Pedestrian Bridges
- International Building Code (IBC) when boardwalks connect buildings
- Speaker estimates 90% of projects use AASHTO guidelines, 10% use IBC
- Vertical Load Requirements:
- Uniform pedestrian load: 90 pounds per square foot (AASHTO)
- Vehicular loads based on boardwalk width:
- Under 7 feet: No vehicular load requirement (but typically design for 5,000 lb gator)
- 7-10 feet: H5 truck (10,000 pound total load)
- Over 10 feet: H10 truck (20,000 pound vehicle)
- Owner-prescribed vehicles/construction equipment often exceed standard requirements
- IBC load requirements: Based on usage, typically 60-100 psf (up to 250 psf for concert/stage uses)
[00:19:00 - 00:24:00] Lateral Loads and Load Combinations
- Wind Loads:
- Most areas governed by 115 mph wind speed
- Coastal areas up to 180 mph
- Special wind areas (e.g., Pike's Peak: 170 mph)
- Critical for both uplift and lateral design
- Seismic Loading:
- Most critical in high seismicity areas (West Coast, Charleston area, Memphis, Hawaii)
- Structural engineer must determine if seismic or wind controls design
- Additional Lateral Forces:
- Braking loads (typically 25% of design truck load)
- Snow loads (example: 240 psf in South Lake Tahoe)
- Hydraulic forces from submerged conditions
- Water velocity and stream debris impacts
- Temperature effects requiring proper detailing
- Load Combinations:
- For pedestrian bridges, simplified to: 1.25 × Dead Load + 1.75 × Live Load
- This is "Strength #1" in AASHTO load combinations
- Represents 25% increase on dead load, 75% increase on live load
[00:24:00 - 00:28:00] Material Design and Specifications
- Reinforced Concrete Design:
- Designed as rigid beam members
- Top portion in compression, bottom in tension
- Steel reinforcement added for tensile loads
- Capacity determined by: amount of steel, beam geometry (width/height)
- Flexible design allows adjustment to specific loading requirements
- Timber Member Design:
- Also uses beam design principles (compression top, tension bottom)
- Utilizes standard dimensional lumber sizes (2×4, 2×6, 2×8, etc.)
- Advantages: Readily available sizes
- Disadvantages: Typically tall and slender, requiring blocking and cross ties
- Limited to approximately 10-foot spans
- Composite Design:
- Many shapes available (solid, scalloped, hollow)
- Material capacities specific to manufacturers
- Requires consulting manufacturer charts for load capacities
- Specifications Importance:
- Critical for communicating design intent
- Provides clear outline of boardwalk components and alignment
- Ensures fair competition among bidders
- Protects owner and designer from non-equivalent alternatives
- Performance specifications or "basis of design" approach recommended
[00:28:00 - 00:31:00] Foundation Selection Overview
- Foundation as Critical Component:
- Potentially the most expensive portion of boardwalk
- Four major components of boardwalk cost:
- Foundation system
- Boardwalk material
- Installation labor
- Railings/curbs
- Geotechnical Report Importance:
- Essential for proper foundation selection
- Several thousand dollars investment usually well spent
- Provides soil analysis through hand augers/soil borings
- Identifies appropriate foundation type for soil conditions
- Prevents guesswork, change orders, and delays
- Helps match foundation loading with soil capacity
[00:31:00 - 00:37:00] Foundation Types
- Foundation Options (Least to Most Expensive):
- Precast pier system (shallow foundation)
- Cast-in-place spread footing
- Timber piles
- Concrete piers (sonos tube with reinforcement)
- Steel helical piers
- Composite piles
- Drilled shafts (caissons)
- Driven concrete piles
- Driven steel piles
- Shallow Foundations:
- Precast footings: Stackable component systems, best for upland soils
- Cast-in-place concrete: Circular or square, extends to frost depth
- Deep Foundations:
- Timber piles: Common, inexpensive, driven/vibrated, installation with lighter equipment
- Fiberglass composite piles: Started in marina environments, light with good vertical load capacity
- Drilled shafts: Common in southeastern/south central US, involves augering, casing, rebar cage, and concrete fill
- Driven steel/concrete piles: Often excessive capacity for boardwalk needs, but necessary for poor soil conditions or deep hard layers
[00:37:00 - 00:41:00] Railings and Add-ons
- Height-Based Requirements:
- Under 30 inches above ground: Curb or no railing acceptable
- Over 30 inches: Handrail required
- Curbs: Used as safety measure to prevent accidental stepping off
- Handrail Height Specifications:
- Pedestrian use: 42 inches high
- Bicycle traffic: 54 inches high
- Design Code Differences:
- Both AASHTO and IBC require:
- 50 pounds per linear foot force at top of rail
- 200 pound point load
- AASHTO: Forces applied together
- IBC: Forces applied independently
- Both AASHTO and IBC require:
- Connection Requirements:
- Based on design forces
- Two-bolt or four-bolt connections
- Railing Aesthetics and Costs:
- Timber railings: Most economical ($50-75 per linear foot)
- Stainless steel cable systems: Premium option (over $300 per linear foot)
- Railing can be major cost driver alongside foundation
- Consider aesthetic fit with surroundings and client preferences
[00:41:00 - 00:44:00] Construction Methods
- Three Primary Construction Approaches:
- Traditional (from ground): Most cost-effective and quickest
- Partial top-down: Foundations built from ground, boardwalk built from top
- Full top-down: Both foundations and boardwalk built from top
- Construction Method Selection Factors:
- Environmental permit conditions
- Site limitations
- Nearby building constraints
- Access issues
- Top-Down Construction Limitations:
- Restricted to 10-12 foot spans
- Limited equipment size/weight
- Equipment must operate on the boardwalk itself
- Resources available on PermaTrak website (articles, videos)
[00:44:00 - 00:48:00] Material Properties Comparison
- Slip Resistance:
- ANSI test protocol measures coefficient of friction
- Minimum passing value: 0.42
- All materials perform well when dry
- Concrete maintains slip resistance when wet
- Wood and composite surfaces become slippery when wet
See our slip resistance study here.
- ADA Compliance:
- Rigid systems (concrete) tend to maintain compliance
- Wood and composite warp over time, potentially creating non-compliant conditions
- Durability:
- Wood/composite: Begin warping within couple years, require maintenance, full replacement in 10-20 years
- Precast concrete: 50-75 year design life with minimal maintenance
- Aesthetics:
- All materials look good initially
- Wood/composite show wear over time
- Concrete offers color and texture options
- Environmental Considerations:
- Pressure-treated timber: Chemicals can leach into soil
- Composites: More eco-friendly but non-renewable, non-biodegradable, not recycling friendly
- Precast concrete: No chemical treatments, long lifespan reduces site impact for maintenance
[00:48:00 - 00:53:00] Case Studies and Applications
- Multi-Use Trail Example:
- 12-foot clear width, 900 linear feet
- Town of Cary, NC standardized on precast concrete for maintenance benefits
- Used wooden railings to soften appearance
- Top-Down Construction Example:
- 450 linear feet, 6-foot clear width
- Equipment size constraints required careful planning
- Avoided need to drain lake or use barges
- Bridge Approach Application:
- Boardwalks commonly used as approaches to longer span truss bridges
- Low elevation example using curbs instead of railings
- Specialized Applications:
- Observation decks for viewing historic features
- High-elevation installation (Pike's Peak at 14,000 feet)
- 45,000 square feet of boardwalk
- Harsh conditions required durable solution
- Modular system advantageous for mountain installation
- Dune crossings: Alternative to typical wooden beach structures
- Rain garden crossings in urban parks
- Curved segments using rectangular and trapezoidal pieces
- Wildlife viewing platforms/observation decks
- Fishing piers
- Tree root protection/crossings (requires arborist consultation)
- Cantilevered designs to avoid waterway impacts
- Replacements for deteriorated timber structures
[00:53:00 - 01:19:00] Question & Answer Session
Top-Down Construction
Q: When should you use top-down construction? What are the advantages and when is traditional construction appropriate in wetlands?
- Recommendation: Avoid top-down if possible (more costly, more time-consuming)
- When necessary:
- Permitting limitations that prevent temporary wetland impacts
- Avoiding 12-18 month Corps of Engineer review process
- Avoiding wetland mitigation requirements
- Limitations:
- Restricted to 10-12 foot spans due to equipment size limitations
- Foundation types limited (helical piers work well but not suitable for rocky soils)
- Option for "partial top-down" where foundations are installed with temporary access mats, then boardwalk installed from above
Tidal and Coastal Installations
Q: What are considerations for boardwalk designs along tidal rivers and ocean fronts?
- Tidal River Considerations:
- Water flow and velocity impacts foundation and structure design
- Moving water creates lateral load requirements
- Salt environment may require epoxy-coated steel
- Permitting and access constraints more complex
- Ocean Front Considerations:
- Salt environment requires epoxy-coated steel and durable concrete mix designs
- Higher wind load requirements in coastal areas
- Wave impact during storm surge difficult to design for economically
- Option to elevate structure above anticipated flood elevation (adds significant cost)
Specifications Support
Q: What kind of specification support is available?
- PermaTrak has experience with 600+ completed projects (90% publicly funded)
- Can share public document examples
- For precast concrete systems, PermaTrak provides engineering that can serve as "basis of design"
- Performance specifications can include allowance for "or equal" alternatives
- For other systems, structural engineers may need to be hired separately
Geotechnical Report Scoping
Q: What should be included in geotechnical report scoping?
- Critical First Step: Understand boardwalk loading requirements and potential span ranges
- For 100-200 foot boardwalk:
- Minimum 2-3 borings recommended
- More may be needed if soil profiles show significant variation
- Maximum 5-6 borings typically sufficient
- Request from geotechnical engineer:
- Evaluation of shallow foundation feasibility with bearing capacity
- Recommendations for deep foundation system if required
- Guidance on skin friction and end bearing for pile systems
- Optional lateral pile analysis for additional information
Common Foundations in Wetlands
Q: What are the most common foundations used in wetland environments? What about vinyl-coated timbers?
- Most common in wetlands: Helical piers (small, light, installable with light equipment, compatible with top-down construction)
- Vinyl-coated timber piles:
- Good option to protect and improve timber pile lifespan
- Particularly useful at water line where exposure creates durability issues
- Common around boat docks
Handrail Requirements in Natural Areas
Q: Are handrails required for boardwalks over 30 inches high in natural area trails?
- Requirement depends on ADA compliance needs and local jurisdiction requirements
- Most owners choose to include railings due to liability concerns
- In remote natural areas, choose less expensive railing options while maintaining safety
- Generally recommended to include railing when over 30 inches high regardless of setting
Component Dimensions
Q: What are the typical dimensions of planks, beams, and other components?
- Planks:
- 4 inches thick (up to 8 feet wide)
- 5.5 inches thick (for wider applications)
- Can go up to 15.5 feet in one piece
- Heavier loading may require 6-8 inch thickness (non-standard)
- Plank length in walking direction:
- Range from 10 inches to 4 feet
- Most common: 2, 3, and 4 feet
- Beams:
- Small series: 9.5 inches tall
- Medium series: 14 inches tall
- Custom beams for spans over 24 feet
- Largest spans (up to 50 feet) may require 27-inch thick beams
Curb Requirements
Q: Are curbs required for boardwalks under 30 inches high?
- Curbs are not required for boardwalks under 30 inches high
- Adding curbs is owner preference and good practice but not mandated
- Beach access boardwalks often have no side protection
Cost Considerations
Q: What are typical square footage costs for concrete systems?
- Total cost includes boardwalk material, foundation, installation, and railing
- Foundation type has major impact on total cost
- Larger projects have lower per-square-foot costs due to distributed fixed costs
- Range: $70-$150 per square foot depending primarily on foundation type
- Critical to get geotechnical report early to make cost-effective foundation decisions
- Strategic design can reduce overall cost (e.g., using custom beams for longer spans to reduce foundation count)
Scour and Erosion
Q: How to address water drainage causing scour/erosion that exposes helical piers?
- Issue requires structural engineer inspection to assess damage
- Possible solutions:
- Pour concrete collar around exposed area
- Replace soil and add riprap protection to prevent recurrence
- Proper design should include scour analysis (using HE-RAS software)
- Foundation should be designed to remain stable even with calculated scour
Licensing and Installation
Q: Do you have licensed structural engineers and what are typical installation rates?
- PermaTrak has access to professional engineers licensed in various states, including Illinois
- No certified contractor requirement - qualified civil site contractors can install
- PermaTrak provides field consultant at project start for contractor training
- First-time contractors can successfully install with proper guidance
- No specific installation rate provided
