How Long Does Pressure-Treated Wood Last Outside?

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Despite its durability, pressure-treated wood can still succumb to harsh elements over time, leaving you with unsightly and unsafe structures. So, it’s essential to understand how long pressure-treated wood lasts to anticipate these concerns. 

For those contemplating using this wood for outdoor project, let me shed light on pressure-treated wood and what you can expect in terms of its longevity.

What to Know About Pressure-Treated Wood: How it’s Treated

The treatment process begins with placing the wood in a large depressurized holding tank, where it is infused with a chemical solution under high pressure to remove wood excess air.

The chemical solution in pressure treatments typically includes copper, which is a natural fungicide, as well as other chemical treatment that resist rot and insect damage.

Types and Lumber Grades of Pressure-Treated Wood

Lumber classified as #1 grade is of higher quality and has a better appearance, with fewer defects such as warping, blemishes, and knots. It is commonly used for visible decking and railing projects due to its premium quality. 

pressure treated lumbers

On the other hand, #2, or construction grade lumber, has a rougher appearance and is usually used for framing and other non-aesthetic projects. 

Benefits, Uses of Pressure-Treated Wood

The benefits of pressure-treated wood are:

  1. Durability: Pressure-treated lumber is treated with chemicals that make it resistant to rot, decay, and insect damage, making it a long-lasting option for outdoor structures. 
  2. Cost-effective: Compared to other wood species, pressure-treated lumber is relatively inexpensive, making it a popular choice for budget projects.
  3. Versatile: Pressure-treated lumber is available in various sizes, types, and grades, making it suitable for various projects.
  4. Low maintenance: It requires minimal maintenance compared to other wood species, making it a convenient option for outdoor application.
deck built with pressure treated wood

Pressure-treated wood is commonly used in the following:

  1. Decks: Treated lumber is a popular choice for deck construction due to its durability, cost-effectiveness, and ease of installation.
  2. Fences: It is a common choice for fencing due to its resistance to rot, decay, and insect damage, making it ideal for long-lasting outdoor structures.
  3. Retaining walls: Treated lumber is often used in retaining wall construction due to its ability to resist water damage and prevent soil erosion.
  4. Playsets: It is a safe and durable option for playset construction, as it can withstand heavy use and exposure to the elements.

The Lifespan of Pressure-Treated Lumber + Indicating Factors

On average, pressure-treated wood last anywhere from 20 to 50 years, depending on the level of exposure to the elements and the quality of its installation. 

pressure treated lumber

In some cases, pressure-treated lumber can last even longer if it is well-maintained and protected from excessive moisture and sunlight. However, the lifespan of treated lumber highly depends on the following factors:

Maintenance

With the right care and maintenance, you can definitely stretch the lifespan of pressure-treated wood. Proper upkeep and attention can prevent damage that may be caused by extreme temperature changes, sun, and rain.

I recommend applying a water-resistant coating approximately six weeks after building the decks and other outdoor structures. And don’t just stop there; make it an annual ritual. This kind of diligence goes a long way in protecting your investment.

Type of Wood

Different types of wood have varying abilities to absorb and retain the chemicals used in pressure treatment. This leads to varying levels of durability when used in different applications. 

Certain wood species are better suited for pressure treatment and are more long-lasting than others. The top-performing wood species for this purpose are:

Douglas Fir lumber

Climate/Temperature

In regions with high humidity or sub-tropical climates, a pressure-treated deck is more susceptible to decay because they absorb moisture and come into contact with damp plants, shrubs, and trees.

Usage

Vertical wood construction usually has a more extended lifespan than horizontal wood projects, as the former can expel moisture more efficiently.

Chemical Preservatives

The pressure treatment process is created by injecting preservative chemicals into the wood in a vacuum-sealed, pressurized tank [1]. 

lumber pressure treated

The type and amount of chemical preservative used and its depth of penetration determine how long the wood will last. But if you want to discard it, can you burn pressure-treated wood? Find answers here. 

Type of Project

The type of project determines the amount and type of wood pressure treatment needed for the wood, which affects its lifespan. 

The amount of preservative required is called “chemical retention levels” and varies depending on the use and stress placed on the wood. 

The Lifespan of Pressure-Treated vs Untreated Deck

On average, a pressure-treated wood deck can last up to 25 years with proper maintenance, while untreated decks may only last 10 to 15 years. 

repainted deck

However, it’s important to note that the lifespan of a deck is influenced by factors such as your area’s climate, exposure to the elements, and your maintenance practices.

What Causes Pressure-Treated Lumber to Rot?

Lack of Air Circulation

Even properly maintained pressure-treated wood rot due to a lack of airflow and moisture buildup, especially in areas close to the ground, surrounded by vegetation, or near water. 

Using UC4 B-treated wood and improving airflow can help prevent rot and retain moisture.

Fungal Infestations

Fungi can cause rot in treated wood, despite initial protection from fungicides in the treatment process. 

mold on wood

Fungi can penetrate the wood and weaken it from within, leading to decay and rot. Regular treatment with fungicides can help protect pressure-treated structures.

Dirt and Vegetation

Dirt and decaying vegetation left sitting on a deck or structural elements can become moisture traps, which isn’t good news for wood. In fact, these trapped seeds can embed themselves into the wood and become catalysts for rot.

To prevent this, it’s important to sweep or wash off dirt and dead vegetation from the structure regularly.

Moisture

Pressure-treated wood rot because of weathering, particularly deck boards, as they expand and contract with seasonal changes. 

moist deck

This can result in cupping or splitting of the boards, which can allow moisture to penetrate deeper into the wood, causing rot.

Applying Paint, Stain, or Sealant Before it Dries

Should You Paint or Stain It?

It is possible to paint or stain pressure-treated wood. In fact, it’s recommended to do so to maintain its quality and durability over time. 

Annual maintenance, such as staining and washing with a high-intensity washer, will help to repel moisture and keep the wood in good condition.

Do You Need to Seal It?

Sealing pressure-treated wood is not always necessary, but it can provide an extra layer of protection against prolonged moisture and UV rays, helping to extend the lifespan of the wood. 

Ready Seal Stain and Sealer for Wood

Sealing is particularly important if the wood will be exposed to the elements or if it will be used in a high-traffic area.

Protecting Pressure Treated Wood + How to Extend its Lifespan

Drying

After the process of pressure treating wood, it takes some time for the wood to dry before painting, staining, or sealing it. It’s necessary to wait for weeks or months before applying these treatments. 

A handy trick I’ve always relied on to gauge if the wood is adequately dry is the water droplet test. Simply sprinkle a bit of water onto the wood; if it soaks in rather than beading up, you know it’s primed and ready for the next step in treatment.

Sealing

Applying sealers that resist or repel water annually and using mildewcide cleaner at first sight of mildew is essential for maintaining the quality of pressure-treated wood. These steps help prolong the lifespan of the wood.

Maintaining

Regular maintenance is required for pressure-treated wood to prevent mildew and rot. Clear snow and leaves regularly, and cut back or prune any plants or foliage near the wood to help it dry more easily.

stairs made with pressure treated wood

Best Pressure-Treated Wood for Ground Contact

UC4A Uses

UC4B Uses

UC4C Uses

Is Pressure-Treated Wood Safe?

Pressure-treated lumber is wood treated with chemicals, including copper-based preservatives like CCA or chromated copper arsenate, were once considered harmful. 

indoor seating bench

However, newer chemicals with less toxic chemicals have been developed for pressure treatment processes like alkaline copper quaternary, and many of the wood industry choose not to use CCA-treated wood. 

Moreover, to avoid risks, it’s important to wear protective gear when handling pressure-treated wood and avoid burning it. 

Bonus Tips When Working with Treated Wood

protective gears

Is there a Warranty Period for Pressure-Treated Lumber?

Yes, pressure-treated lumber usually comes with a warranty period, but the specifics can vary depending on the manufacturer and the product. In general, the warranty period for treated lumber can range from 20 to 50 years or more.

More about pressure-treated wood:

Conclusion

Knowing how long does pressure-treated wood last is beneficial if you are considering using this type of wood for outdoor projects. 

While its lifespan can vary based on several factors, it generally offers a longer lifespan than untreated wood. However, like any other wood, it still requires proper care and maintenance to ensure longevity.

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Robert Johnson is a passionate furniture maker & carpenter, sought after for his knowledge on the craft.
You’ve probably seen his down-to-earth wisdom in USA Today, Bobvila, Family Handyman, and The Spruce, where he has shared commentary and guidance on various woodworking topics.

Robert is the brain behind Sawinery, where he aims to share tips, tricks, and a passion for all things carpentry.

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