marine grade lumber

What Is Marine-Grade Lumber?

When it comes to woodworking, medium-density overlay (MDO) lumber is often enough for the job. As a result, contractors use this all-purpose building material in many different applications. But when it comes to marine environments, think again.

You’ll need to invest in marine-grade lumber for docks and other marine uses, like seawalls and water walkways. But what makes lumber marine-grade, and why is that so important?

What Is Marine-Grade Lumber?

Marine-grade lumber is wood you can use for water applications, both near or in the water. The wood goes through a unique treatment process to make it acceptable for use in various marine environments. There are specific types of wood for saltwater applications and others for freshwater applications.

Let’s explore the difference between marine-grade lumber and pressure-treated lumber.

Marine-Grade Lumber vs. Pressure-Treated Lumber

Considering marine-grade lumber goes through a treatment process, you may think these two wood types are the same. However, there are distinct differences between marine-grade and pressure-treated wood, as shown.

Natural Marine Timbers

Most docks use marine lumber because not just any wood will do for piles. Being constantly submerged in water means piles require either treated softwood or hardwood.

Treated softwood is affordable and customizable, making it popular. However, it can still be vulnerable to decay and marine pests. Some common softwoods include:

  • Cedar
  • Douglas fir
  • Pine
  • Redwood

On the other hand, hardwoods, like Greenheart, are naturally strong and have protection against water corrosion and rot. Therefore, they don’t require pressure treatment.

Marine-Grade Pressure Treatment for Lumber

Pressure treatment describes the process of fortifying natural lumber against mold, rot, and pests. A unique chemical treatment penetrates deep into the wood fibers. The most common chemical in the treatment is copper.

There are many types of pressure treatments, creating wood that you can use for various applications.

How Long Does Marine-Grade Lumber Last?

Experts say high-quality marine-grade lumber can last up to 30 years or more with proper maintenance.

Using EPA-approved wood preservatives and sealants can make your lumber last even longer. When looking at the lumber label, pay attention to the type of preservative on the treated wood. Different preservatives work best for various applications. The most common treatments are:

  • Alkaline copper quaternary (ACQ)
  • Chromated copper arsenate (CCA)
  • Micronized copper azole (MCA) and copper azole (CA)

The APWA Classification System

The American Wood Protection Association (APWA) sets the standards for treated wood in residential and commercial applications. Although APWA standards are only informational, many building code laws reference them at the federal, state, and local levels. Thus, it’s imperative to understand the classification system when purchasing lumber for your project.

For example, if you’re undertaking a marine construction project, you only want to use a classification of UC4A or greater. This classification proves the wood is water-resistant. 

Conversely, those working specifically in saltwater should look for the UC5B and UC5C classifications. While you may use UC4B for a freshwater boardwalk, you’ll need something with more durability for saltwater deck boards.

Remember that saltwater environments also require stainless (not galvanized) steel for the fasteners.

By understanding the standards listed here, you’ll have a much better idea of the type of wood to use for your project.


Contractors typically use UC4A in the following applications:

  • Crossties
  • Decking
  • Fencing
  • Guardrail posts
  • Utility posts in low-decay areas

The wood will withstand exposure to regular weather cycles but can succumb to decay, fungi, and insects with time.

The service conditions are:

  • Freshwater
  • Ground contact
  • Non-critical components


Common uses for UC4B wood are as follows:

  • Building poles
  • Crossties
  • Horticulture posts
  • Permanent foundations
  • Utility poles

Like UC4A, UC4B wood can withstand exposure to regular weather cycles but can also resist high decay. This includes splashes of saltwater (not submerged). However, the wood can still experience decay, fungi, and insects with an increased potential for biodeterioration.

The service conditions are:

  • Freshwater
  • Ground contact
  • Critical components or difficult replacement areas


UC4C is standard for the following applications:

  • Crossties
  • Foundation piling
  • Land piling
  • Water piling
  • Utility poles in high-decay areas

Unlike the other UC4 classifications, UC4C can withstand severe environments, including those with extreme decay potential. However, that increases its likelihood of biodeterioration.

The service conditions are:

  • Freshwater
  • Ground contact
  • Critical structural components


UC5B describes wood for these saltwater applications:

  • Bracing
  • Bulkheads
  • Piling

It’s the ideal classification for continuous marine exposure. But, it may succumb to saltwater organisms, such as Limnoria Tripunctata.

Thus, UC5B is best for salt or brackish water on the east coast from New Jersey to Georgia.


UC5C has the same applications as UC5B but is best for salt or brackish water on the east coast, south of Georgia, and along the Gulf.

It, too, has the potential to deteriorate from saltwater organisms like Martesia and Sphaeroma.

How Do You Choose the Right Marine-Grade Lumber?

To guarantee you choose suitable lumber for your project, consider the following questions:

  1. What kind of water is in the construction environment?
  2. What’s the weather like? Are there frequent hurricanes?
  3. Does the water freeze in winter?
  4. How much boat traffic is there?
  5. Is the project residential or commercial?

By further understanding the conditions of your project, you will know which marine lumber to choose using the APWA classification system. When in doubt, ask our professionals for advice.

Get the Marine-Grade Lumber You Need for Your Project

If you need assistance with any dock construction undertaking, including DIY projects or a special order, get in touch with us at Harbor Exports today. Our team is happy to answer your questions, point you in the right direction, and assist you with your next marine project.

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