Here's What Matters: We'll discuss the importance of choosing the right lumber, installing joists at a good spacing, the importance of waiting for your floats, and why you should reinforce with stringers.
When you're building a floating dock, the framing is the backbone of the entire structure. It's what keeps everything square, solid, and ready to use. Doing the work on the front end can help save you from those headaches down the road.
IMPORTANT NOTE: You can skip most of this blog, if you want! Go and check out our DIY Kits, where we've done all measuring and layout of your frame, you just have to assemble it!
A Few Key Definitions:
Not everyone uses the same terminology in dock building. For the sake of this clarity we are using the following terms:
- Outer Frame: The border of the dock. This outer frame dictates the total square footage and squareness of the dock platform.
- Joists: The beams that run perpendicular to the decking and stringers, and is used to support the outer frame, your floats, and your decking.
- Stringer: A piece of lumber running under the joists, attached with hardware, that helps prevent warping of the joists.
Dock Frame Materials: What You Can Use (and What Most DIY'ers Choose)
Dock frames can be built from a variety of materials; galvanized steel, aluminum, and composite systems. Pressure treated lumber is the go-to for the vast majority of DIY dock builders. It’s strong, cost-effective, and easy to work with.
Most DIYers build their frames with 2×6 treated lumber (This is what our DIY Kits are designed for). It hits the sweet spot between strength, weight, and generally gives you the best bang for your buck.
Joist Spacing: 12", 16", or 24" on Center?
Joist spacing (or “on center,” meaning the distance between joist centers) determines how stiff your dock will feel underfoot:
- 12" OC (Heavy Duty): Maximum structural integrity; transfers the primary load to the frame for a rock-solid feel.
- 16" OC (The Standard): The ideal balance of performance and material efficiency for most residential projects.
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24" OC (Light Duty): Budget-friendly spacing for low-impact areas; relies more heavily on the decking material's span strength.
We base our DIY dock kit calculations on 16" OC Max, because it balances strength, weight, and cost in the most efficient way.
A note about 24" joists- Unfortunately, most decking is not designed to support a 2' gap between joists. It's important to confirm decking tolerances before designing & building.
Why You Should Always Wait for Your Floats Before Framing
Manufacturers list standard dimensions, but rotationally molded floats can vary slightly up to 1–2% in size. That’s totally normal, but if you frame based on catalog dimensions instead of the floats sitting in front of you… well, you may end up with joist spacing that doesn’t match your float’s mounting pattern. Its critical that the outer frame and joist align with four dock float mounting locations.
You can learn more about attaching floats HERE.
Stringers vs. Blocking: Preventing Long-Term Warping
Pressure treated lumber isn't what in once was. In marine environments and under a non stationary load the lumber will want to warp over time. A stringer is a support board that runs perpendicular beneath your joists. Its job is simple but critical as it:
- Prevents joists from warping
- Keeps the dock rigid
- Adds long-term structural integrity
Some builders prefer blocking (short pieces installed between joists) but we find stringers to be easier and better for maintaining straight joist. Here is an image of a blocking example.
That’s why our Dock Kits include the hardware for stringer installation. It’s the method we trust for durability and stability.
Your dock may require more or less support depending on the environment. In general, adding a stringer gives you extra security to know your dock is built for the long haul.
Final Thoughts
A well-framed dock makes every other step of the build easier. When you choose the right lumber, install joists at a good spacing, wait for your floats, and reinforce with stringers, you end up with a dock that’s sturdy, square, and built to last for years.
If you’re ready to dive deeper into the DIY process or want help picking floats and hardware, reach out on our Contact Us page.
