A pressure-treated wood item that has been subjected to high amounts of chemicals will last anywhere from 15-20 years before it begins to show signs of wear and tear. Pressure-treating a piece of timber with chemicals makes it quite durable to survive outdoors. However, over time these chemicals will break down and the wood will become more susceptible to damage from weathering, rot, and insects.

How Long Will Pressure-Treated Wood Last In The Ground?

Pressure-treated wood that is in contact with the ground will have a shorter lifespan than pressure-treated wood that is not in contact with the ground.

The chemicals in pressure-treated wood are designed to protect the wood from rot and decay, but they will eventually break down.

Expect pressure-treated wood in contact with the ground to last around 10-15 years before it needs to be replaced.

Related: How Does Pressure-Treated Wood and Lumber Work?

How Long Will Pressure Treated Wood Last Above Ground?

Pressure-treated wood that is not in contact with the ground will last much longer than pressure-treated wood that is in contact with the ground.

The chemicals in the pressure-treated wood will protect the wood from rot, decay, and insects.

Expect pressure-treated wood that is not in contact with the ground to last 15-20 years before it needs to be replaced.

How Long Does Pressure-Treated Wood Last if It’s Not Treated?

Pressure-treated wood will not last as long as untreated wood. Pressure-treated wood is impregnated with biocides that make it resistant to decay, moths, and other pests.

Untreated wood will not have these chemicals and will therefore not last as long. Expect untreated wood to last around 10-15 years before it needs to be replaced.

What is the Best Way to prolong the Life of Pressure-Treated Wood?

There are a few things you can do to prolong the life of your pressure-treated wood.

First, if the wood is in contact with the ground, make sure to put a layer of mulch around it. This will help protect the wood from moisture and rot.

Second, if you are going to paint or stain your pressure-treated wood, make sure to use a quality product that is designed for pressure-treated wood.

Third, if you have pressure-treated wood that is not in contact with the ground, make sure to clean it and inspect it regularly.

If you see any signs of rot or decay, make sure to repair it as soon as possible.

Related: Things You Need to Know Before Repairing Your Deck

Pressure Treated Lumber Grades

Pressure-treated wood comes in four grades: Premium, Select, Number 1, and Number 2.

The fewer the flaws, the higher the grade; that is, splinters or knots. For decks, in particular, you should select Number 2 grade boards or higher since they will have fewer faults.

The highest grades, which are Premium and above, have the greatest grain, strength, and appearance.

Because of the expense, these timbers are rarely utilized in-country. The majority of 5/4 decking is a mid-range grade – somewhere between #1 and #2 lumber or a combination of the two.

If you don’t want to settle for anything less than #2 construction grade pressure-treated wood, you’ll have to choose and pick from a very restricted variety.

If the wood was wet after being treated with a chemical solution, it will shrink as it dries, producing cupping, curling, warping, and bow. When purchasing treated timber with an ECA (such as ACQ) always check the label to see if it is kiln-dried or air-dried.

Kiln-drying removes most of the moisture from the wood, reducing the possibility of warping and cupping.

Air-drying can take up to two years, so there is a greater chance that the lumber will warp or cup.

Construction grade pressure-treated lumber is the least expensive and is often used for structural purposes such as framing, beams, joists, fence posts, and decking.

The wood is not as smooth as premium grades and may contain knots or other imperfections.

The Best Pressure Treated Wood for Ground Contact

When wood comes into direct contact with the ground or vegetation, it is within 6 inches of the ground, or it is placed where it sits in, on, or over freshwater (water), wood will have a moist heat seal.

The use of treated wood to build your project will increase its longevity and safeguard your investment.

The best pressure-treated wood for ground contact is UC4A, B, or C, depending on the sort of contact.

UC4A has more chemicals per cubic foot of wood than the previous categories, and UC4B contains more chemicals than UC4A.

Meanwhile, while the amount of chemicals in each category is equal to or less than that seen previously, it is greater than in the previous three categories.

UC4A uses:

  • Nominal exposure to decay.
  • Within 6 inches of the ground is ideal.
  • Ground contact is light.
  • Dampness, exposure to a lot of moisture, or living in a tropical region
  • Contact with wet leaves or vegetation that has been standing for an extended period of time.
  • If there is a lack of airflow or circulation.
  • If boards, joists, beams, or posts are difficult to replace, repair, or maintain on a ledger system.
  • Decking, stringers, and boardwalk materials.

UC4B uses:

  • Docks and piers that are intended to last for an extended period of time.
  • High potential for decay.
  • Wood foundations.
  • Contact with salt water spray or freshwater such as marine structures.
  • Difficult to replace framing members and heavy-duty functions.
  • Heavy duty functions or difficult to maintain or replace framing members.
  • Utility poles, cross-ties, or garden posts are all possible alternatives.
  • Exposure to the tropics or all types of weather cycles.

UC4C uses:

  • Direct contact or installation in concrete, gravel, or earth
  • Contact of structural components – Ground or freshwater.
  • High potential for decay.
  • Exposure to the tropics or all types of weather cycles.
  • Utility poles, cross-ties, or garden posts are all possible alternatives.
  • Land, building pilings, and freshwater.
  • Utility poles and cross-ties in areas of severe decay potential.

FAQs

Can you paint pressure-treated wood?

Yes, you can paint pressure-treated wood, but it is not necessary. The pressure treatment process already provides a layer of protection against the elements. Painting pressure-treated wood can also seal in any chemicals that may be harmful to the environment.

Can you stain pressure-treated wood?

Yes, you can stain pressure-treated wood, but it is not necessary. The pressure treatment process already provides a layer of protection against the elements. Staining pressure-treated wood can also seal in any chemicals that may be harmful to the environment.

What is the best way to clean pressure-treated wood?

Pressure-treated wood should be cleaned with a pressure washer, ideally setting the pressure to no more than 1,500 psi. A garden hose with a nozzle attachment can also be used to clean pressure-treated wood.

In Summary

Pressure-treated wood is a must for many outdoor construction projects, but it demands special treatment and maintenance than other woods.

Be sure to kiln-dry pressure-treated lumber before using it, and don’t forget to use the right chemical solution depending on the application.

With proper care, your pressure-treated wood project will last for many years.

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