Dock and Marina Lumber: Species, Treatment and Hardware
Dock and marina framing lives in the harshest exposure any wood structure faces: constant wetting, UV, abrasion from boats and feet, and in salt water, marine borers that can destroy untreated wood in a single season. Material selection here is less about appearance and more about matching treatment retention and fastener metallurgy to the water you are building in.
Key Takeaways
- Treatment retention level, not just "pressure treated", is the specification that matters for marine use
- Salt water exposure requires higher retentions and, for pilings, dual treatment in borer-heavy regions
- Tropical hardwoods work well as dock decking but should not be substituted for treated structural members below water
- Use Type 316 stainless or hot-dip galvanized hardware rated for the exposure — standard coated deck screws fail quickly
Understand exposure before choosing material
Three exposure zones exist on almost every dock. Above-water framing and decking see wetting, spray and UV. The splash and tidal zone cycles wet and dry, which is the most aggressive zone for decay. Permanently submerged members face marine borers in salt and brackish water, and bacterial decay in fresh water.
Freshwater lakes and rivers are considerably more forgiving than coastal salt water. In salt water, teredo and pholad borers and gribble attack submerged wood, and a piling specified for a freshwater lake will not survive the same service life in a coastal marina.
Pressure treated lumber and retention levels
Preservative-treated Southern Yellow Pine is the default structural material for dock framing and pilings across most of the US. The important number is retention — the amount of preservative retained per cubic foot of wood — which is matched to the use category by the treating standard.
Ground-contact deck lumber sold at a general lumberyard is usually treated for above-ground or ground-contact use, not for immersion. Marine-use material is a different product and often a special order. Always confirm the retention and use category on the end tag rather than assuming.
- Above-water framing and decking: ground-contact rated treated lumber is generally appropriate
- Freshwater immersion: a higher retention rated for fresh water immersion
- Salt water immersion: marine-grade retention; dual treatment (creosote over waterborne, or comparable) is common for pilings in high-borer regions
- Field cuts and drilled holes must be brush-treated with an approved end-cut preservative
- Creosote and heavy oil-borne treatments carry handling and jurisdictional restrictions — confirm local rules before specifying
Decking options
Dock decking takes abrasion, bare feet and standing water, so hardness, splinter resistance and slip behavior when wet all matter more than they do on a residential deck.
Dense tropical hardwoods perform very well in this role. Ipe, Cumaru and Massaranduba resist wear and decay, hold up under sun and spray, and stay dimensionally reasonable when detailed with proper gaps. They are decking, not substructure — use treated or engineered marine members for framing and pilings.
- Ipe: hardest and most durable of the common options; pre-drill everything, expect silver-gray weathering
- Cumaru: similar performance at lower cost; acclimate on site, allow slightly larger gaps for movement
- Massaranduba: excellent in humid coastal exposure; can check in hot, dry sun
- Treated Southern Yellow Pine 5/4x6: lowest cost, widely available, expect more maintenance
- Western Red Cedar: pleasant underfoot and stable, but soft — better on light-duty freshwater docks than commercial piers
Hardware and fasteners
Fasteners fail before lumber does on most poorly built docks. Modern waterborne wood preservatives are more corrosive to metal than older formulations, and salt spray accelerates everything.
Type 316 stainless is the appropriate choice for salt and brackish exposure. Type 304 stainless or hot-dip galvanized hardware rated for treated lumber is generally acceptable in fresh water. Electro-galvanized screws, standard coated deck screws and mixed metals in contact are all reliable ways to produce rust streaks and failed connections within a few seasons.
- Salt/brackish water: Type 316 stainless fasteners, bolts, brackets and hidden clips
- Fresh water: Type 304 stainless or hot-dip galvanized rated for contact with treated lumber
- Use through-bolts with washers rather than lag screws at structural connections where possible
- Avoid dissimilar metals in direct contact — galvanic corrosion attacks the less noble metal
- Isolate aluminum framing components from treated lumber with an approved barrier
Permits and environmental rules
Building over water is regulated. Depending on location, a dock may require approval from a state environmental agency, a local conservation commission, and in navigable US waters the Army Corps of Engineers. Rules commonly restrict which preservatives may be used over water, how much surface area you may cover, and when in-water work may occur.
Confirm the permitted materials list before ordering. It is common for a jurisdiction to prohibit a treatment type that is otherwise standard elsewhere, and preservative-treated material is generally not returnable once cut.
Specifying a dock material quote
Marine material is frequently a special order with real lead time, so give suppliers the exposure details up front.
- Salt water, brackish or fresh water
- Whether members are above water, in the splash zone, or submerged
- Piling diameter, length and required retention, if pilings are in scope
- Decking species, profile and total square footage
- Fastener metallurgy required by your jurisdiction or engineer
- Site access for delivery — long pilings and timbers need room to offload