Thank you to everyone who attended our "How to Build a Boardwalk Through a Wetland" webinar. The questions and engagement from the audience made for a great session!
In case you missed it, here is the full webinar recording from May 13, 2026.
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 Speaker Bios
- 01:50 - PermaTrak System Overview
- 03:20 - Why Top-Down Construction Matters
- 06:35 - Drivers for Top-Down: Permits, Site Conditions, Equipment Limitations, and Wildlife
- 11:15 - Key Permit Language to Watch For
- 13:55 - The Four Construction Methods Explained
- 17:50 - The Three Types of Top-Down Construction
- 21:40 - Cost Impact by Method
- 23:20 - Material Comparison: Timber, Composite, and Precast Concrete
- 24:40 - Case Study 1: Jean Lafitte National Park (Partial Top-Down)
- 27:25 - Case Study 2: Shot Pouch Greenway, Sumter, SC (Helical Piers)
- 31:00 - Case Study 3: Panther Creek Greenway, Cary, NC (Vibrated Timber Piles)
- 34:00 - Specification Language and Bid Document Considerations
- 43:25 - How PermaTrak Supports Your Project
- 45:15 - Q&A Session
Check out:
- Our full written guide on how to build a boardwalk over wetlands using top-down construction, including cost comparisons and method breakdowns, at permatrak.com
- Download the slides used during the webinar
How to Build a Boardwalk Through a Wetland - Detailed Key Takeaways
[00:03:20] Why Top-Down Construction Matters
Top-down construction comes up on the majority of wetland boardwalk projects, but it is actually required far less often than designers assume. Of the 750+ structures PermaTrak has installed, top-down was discussed on roughly 60% of them but was ultimately used on only about 7%. Understanding the difference between when it is a need versus a want is one of the most important decisions a design consultant can make, and the best time to make it is during the design phase, before permits are finalized and bids go out.
[00:06:35] Drivers for Top-Down Construction
Several factors can push a project toward top-down construction:
- Permit requirements under Clean Water Act Section 404 and Army Corps of Engineers Nationwide Permits (NWP 10, NWP 14) that restrict equipment in wetlands or limit clearing outside the boardwalk footprint
- Site conditions such as steep slopes, roadway adjacency, or locations where conventional equipment simply cannot operate
- Equipment limitations that prevent cranes or large machinery from reaching the site
- Heritage or protected trees where arborists restrict what equipment can operate over root systems
- Sensitive wildlife habitats with seasonal work windows or time-of-day restrictions
The key takeaway: review permit draft language carefully and ask for clarity. Language like "no equipment in the wetland" is very restrictive and costly. "No clearing outside the footprint of the structure" gives contractors more flexibility and results in a more manageable bid.
[00:17:50] The Three Types of Top-Down Construction
Not all top-down construction is the same. There are three distinct methods, each with different cost and schedule implications:
- Partial Top-Down: Foundations are installed from the ground first, within the permitted footprint. Once complete, the contractor backs out and the boardwalk is installed from the top down. This is the most cost-effective top-down method and can achieve installation rates of 100 to 150 linear feet per day under good conditions.
- Full Top-Down with Helical Piers: The entire operation, including foundation installation, is performed from the top of the boardwalk as it is built. Helical piers are installed with equipment reaching out in front of the work area. This method is slower, typically producing 10 to 40 linear feet per day, and works best when geotechnical conditions support helical pier use.
- Full Top-Down with Vibrated Piles: Similar to the helical pier method but uses vibrated timber or composite piles instead. Requires heavier equipment on the boardwalk deck and is typically used when driven piles are not feasible due to site constraints such as overhead clearances.
[00:21:40] Cost Impact by Method
Construction speed directly drives cost. Traditional ground-based construction is the baseline. Partial top-down adds a moderate premium. Full top-down with helical piers or vibrated piles adds the most significant premium, primarily due to the slower pace of installation. When evaluating budget early in design, consider running cost scenarios for multiple methods rather than assuming one approach.
[00:23:20] Material Comparison: Timber, Composite, and Precast Concrete
- Timber is the most common boardwalk material and offers flexibility in the field since members can be cut and adjusted on site. However, once boardwalk widths exceed 10 feet and H10 loading is required, timber members must increase significantly in size and complexity.
- Composite materials are less commonly used in commercial applications and offer moderate durability advantages over timber.
- Precast concrete offers the highest structural capacity, standard component sizing, and the ability to design members specifically for construction equipment loads, which is a major advantage in top-down scenarios.
[00:34:00] What to Include in Your Specifications
Clear spec language is one of the most effective tools for protecting your owner and getting consistent, comparable bids. Key items to address:
- Which top-down method is required or allowed
- Allowable equipment type and weight
- Construction live load assumptions (AASHTO H5 or H10, or a project-specific construction load if heavier equipment is anticipated)
- Whether mats are permitted and where
- Construction sequencing requirements for partial top-down
When construction equipment loads exceed H10 (20,000 lbs), the boardwalk structure and foundation must be designed to account for both the increased axial load and the additional lateral load. Specifying the assumed construction load upfront puts all contractors on the same footing and reduces the likelihood of change orders after award.
[00:45:15] Q&A Session
Does top-down construction always require stronger or larger beams?
- Standard PermaTrak beams (14 inches tall, 20 feet long) can generally handle construction equipment under 20,000 lbs without changes to beam dimensions or reinforcing
- Above that threshold, additional rebar may be required but beam dimensions typically stay the same
- The key is specifying the assumed construction load clearly in bid documents so any contractor proposing heavier equipment understands it may result in a material cost premium
How deep can helical piers be installed during top-down construction?
- Helical piers are segmental, with sections typically ranging from five to seven feet bolted together as they go deeper
- Most installations fall in the 20 to 30 foot range; beyond 30 feet, an alternate foundation type is worth evaluating
- PermaTrak does not design helical pier systems; that is a delegated design handled by specialty subcontractors
- A load test is recommended to confirm capacity before full production installation begins
Can precast foundations be used for top-down construction?
- Standard precast driven piles are generally not compatible with top-down construction because they require large crane-based pile driving equipment
- Cast-in-place concrete piers can work in partial top-down scenarios when footprint disturbance is permitted
- Helical piers and vibrated timber or composite piles are the most practical foundation options for full top-down applications
How does PermaTrak handle publicly bid projects where sole sourcing is not allowed?
- 725 of PermaTrak's 750+ installed structures have been on publicly funded projects
- Consultants typically specify a precast concrete boardwalk system with PermaTrak listed as the basis of design, or use performance-based language describing the system requirements
- PermaTrak is the only precast concrete boardwalk system in the United States with a dedicated engineering staff
- PermaTrak can share specification examples from major consulting firms on request
What finish and texture options are available for the decking surface?
- Two standard textures are available: a timber-look texture and a sand texture, both cast directly into the tread using a form liner
- Both textures have been third-party tested for slip resistance and perform well when wet
- Standard color options include Melbourne Tan, Adelaide Gray, and a premium color called Savannah Brown
- Natural (unpigmented) concrete is also available
- Custom colors and textures beyond the standard offerings are available at additional cost
