How Long Does Pressure Treated Wood Last?

Pressure treated wood is a famous deck-building material, thanks to its impressive durability. However, various factors affect the lumber’s longevity.

Today, let’s look at how long does pressure treated wood last?

Pressure treated wood experiencing wet-dry and freeze-thaw cycles will last about ten years.

But it can go up to 40-plus years with proper maintenance and treatment.

In addition, many suppliers warranty their treated lumber for 30 years against insects and rot.

Factors such as climate, the type of wood, its uses, and how well it’s maintained are the major players in the durability of pressure treated wood.

The wood type and its uses also affect pressure treated lumber’s longevity. Therefore, read this article to learn about the material and how to get the best from it.

What Is Pressure Treated Wood?

Image of wolmanized wood, but Is Wolmanized Wood the Same as Pressure Treated?Pressure treated (PT) wood undergoes chemical treatment to enhance its resistance to insect infestation and fungus growth.

Manufacturers place the wood in a depressurized holding container and use a high-pressure vacuum to remove wood moisture.

Then, they infuse chemical preservatives in the lumber’s grain.

Generally, pressure treating means immersing wood in a liquid preservative. And then subject it to high pressure.

The chemicals keep the wood termite resistant and rot-free. So, you can expect it to stay longer than natural lumber.

Woodworkers have used different compounds and oils to preserve wood throughout history. For instance, the ancient Greeks utilized olive oil, while the Romans used tar.

Railway companies also began large-scale wood pressure treatment in the last half of the 19th century. They used creosote to protect bridge timbers and ties.

Modern pressure treatment involves soaking the wood in a water-based chemical bath. Then, put it under high pressure in a cylindrical chamber.

This way, you force the solution deeper into the lumber’s cell structure. And the water evaporates, leaving the preservative behind.

The wood also undergoes incision. The process involves making minor cuts into the wood’s surface for deeper penetration by the chemicals.

However, creosote and oil-based chemicals leach out over time. Hence, although they are acceptable for industrial use, they are too toxic and messy for residential use.

Suppliers have three pressure treatment categories for lumber.

  • Waterborne Chemical Infusion primarily works for wood in residential, commercial, and industrial construction.
  • Creosote Treatment is suitable for marine timber structures, railway ties, and guardrail posts.
  • Oil Treatment is less frequent today but mainly works for utility posts.

Some famous wood preservatives include Ammoniacal Copper Zinc Arsenate (ACZA), Copper Azole, Borates, Alkaline Copper Quart (ACQ), and Chromated Copper Arsenate (CCA).

Here is a summary of each preservative.

  • Chromated Copper Arsenate (CCA)

CCA is a chromium, copper, and arsenic mixture that turns lumber green. Further, it is a common preservative from the mid-1930s to 2004.

However, an EPA study in 2000 confirmed the chemical was too hazardous for household use.

Therefore, the lumber industry stopped using it for residential purposes in 2003.

  • Micronized Copper Azole (MCA)

MCA is eco-friendly and water-based, making it a safe alternative to CCA. In addition, it is excellent for animals and humans.

But please avoid using it with food or animal feed.

The preservative protects against mold, fungus, mildew, insects, and rot. 

It also gives the lumber a light brown hue and works best for in-ground, above-ground, and fresh-water contact locations.

  • Borate

Borates refer to the sodium salts in water-based pressure treatment formulas.

Though they do not discolor the lumber, the surface will enjoy unmatched protection against rot and elements.

Unfortunately, the chemical’s water-soluble attribute makes it prone to leaching out in wet and rainy regions.

But they are an ideal preservative for wood in arid areas.

  • Alkaline Copper Quaternary (ACQ)

ACQ is an environmentally safe chemical featuring soluble copper and quaternary ammonium alkyl.

Also, the manufacturer can use substitute compounds depending on the desired outcome.

This solution protects the lumber from fungus, insects, rot, mold, and mildew. In addition, it gives the surface a brown hue.

However, ACQ should not contact food or animal feed.

NB: All copper-based lumber preservatives corrode unprotected steel and iron fasteners or brackets.

Thus, use bituminous tape or tar paper to protect hot-dipped galvanized or stainless steel materials and metal brackets. 

Moreover, treat all cuts and drilled holes with chemicals to preserve exposed untreated wood.

The above compounds treat various wood types, including Douglas Fir.

Besides, we have an oil-type chemical preservative for pressure treatment. It delivers oily lumber surfaces and is suitable for pilings and utility poles.

But the formula gives the wood an unpleasant odor. Thus, consider using it for applications with minimal human contact.

Pressure treated wood has come a long way in the past century. Even better, the current process is computerized and mechanized with modern technology.

Therefore, it is much easier and yields a lasting outcome.

Finally, the treated lumber undergoes natural or kiln drying before shipping to the retailer.

So, the preservative remains in the material and fortifies it against mildew, mold, fungal growth, insects, and rot.

Types of Pressure Treated Wood

Many DIYers and even some woodworking professionals do not know different pressure treated wood types.

Moreover, various lumber categories have numerous uses, and the information stapled on the end tag may not be enough.

Hence, walking into a wood store or lumberyard can be daunting.

Pressure treated lumber comes in different types depending on its retention level and the preservative amount retained after treatment.

We measure the retention level in pounds of chemical per cubic foot of wood (PCF). 

The longer the lumber is in the pressure chamber, the more the chemical preservatives are forced and retained in the wood grain.

Pressure treatment does not make the lumber stronger or weaker. It only adds more insect and moisture damage resistance.

Thus, the more the chemical amount is retained in the material, the more resistant it becomes.

Furthermore, the American Wood Protection Association (AWPA) sets the retention level standards appropriate for different lumber types.

It also regulates different chemical preservative compositions depending on the wood’s specific use.

This unified rating helps in identifying the wood. Furthermore, the lumber’s end-tag tells how well it can withstand different conditions, regardless of its chemical cocktail.

We have five different pressure treatment ratings used in categorizing wood.

Each type identifies the chemical retention, determining where and how to use the lumber.

For instance, use UC3A pressure treated wood for above-ground exterior projects. But ensure that the lumber is six inches above the ground.

The wood also needs good air circulation and drainage to guarantee longevity.

Conversely, use UC3B or UC4A for ground contact applications. These projects include anything within six inches or in direct contact with the ground.

You can use this wood for areas with poor air circulation and drainage or for sill plates that are difficult to maintain or repair.

Pressure treated wood for ground contact projects possesses twice the chemical retention of above-ground-rated lumber.

Alternatively, go for in-ground lumber like UC4B and UC4C. They have a higher retention rate than lower graded types.

Use in-ground type wood whether you have a greater deterioration risk. It also withstands severe environmental exposure.

Further, you can utilize the material for critical structural parts like foundation and utility posts.

Lastly, heavy-duty wood is perfect for seals, docks, and other marine applications.

What Are the Different Grades of Pressure Treated Wood

Pressure Treated Wood. can you paint pressure treated wood?Trained inspectors often grade wood at lumber mills for quality control and structural strength.

They evaluate the lumber’s knots, splits, and other flaws compromising its integrity.

All structural wood in Canada and the U.S. need a stamp identifying its grade. These grades may be SS, #1, #2, or #3.

Further, building codes, engineers, builders, and other professionals use wood grades to ensure the structures are safe.

Some lumber mills prefer to identify pressure treated wood as A, B, C, or D depending on blemishes and knots on the surface.

However, there is no standard for grading the lumber’s appearance.

Thus, Select and Premium options could be 1 or #2 structural grade, but with an increased cost.

The knot’s number, size, location, moisture content, and the wood grain’s slope determine the lumber’s grain.

In addition, the wood stamps identify the wood’s inspection organization, mill, wood species, moisture content, and grade.

Below are pressure treated wood grades and categories.

  • Premium Grade

Premium grade refers to wood types with few or no knots and blemishes. It capitalizes on DIYers’ wish to get better-looking lumber.

There is no structural premium grade. It’s only a term for bright-looking lumber free of knots and blemishes.

Besides, this wood category has impressive structural strength but fewer flaws. As a result, it has a better appearance.

Premium wood types are often available as #1 or #2-grade lumber.

You can identify it as A, B, C, and D. Type’ A often has no visible splits, knots, or defects, whereas ‘B features few minor blemishes.

Conversely, ‘C has tiny knots on one side and none on the other, while ‘D may have pin-size knots on both sides.

The treated lumber’s transparent appearance makes it perfect for cabinetry, trim, and furniture.

Its appearance needs to be 80% free of blemishes.

  • Select Structural

SS is the highest pressure treated wood grade based on durability and strength. Further, it features a grain slope of one in 12.

The lumber also has seasoning checks and tight, well-spaced knots of up to 2¼ on a two times eight.

Select grade wood has a knothole every four inches and is more potent than #1 or #2.

Moreover, it is perfect for all structural constructions and can span extended distances. For example, SPF SS 2×8 reaches 15’-3″.

Lastly, the lumber’s appearance is also 80 percent free of flaws,

  • Grade #1 Structural 

Wood structurally graded #1 & BTR (#1 and better) or #1 has a wood grain slope of one in ten.

It is more robust than #2 or #3-grade lumber. In addition, you’ll find well-spaced and tight knots to keep them from falling out.

The knots are also less prominent, say 2¾ inches in a 2×8 board.

Grade #1 Structural wood may have a hole every three inches. And an SPF #1 2×8 spans distances between 14 to 11 inches.

The lumber’s appearance requires it to be 75 percent free of defects and knots.

  • Grade #2 Structural

Generally, grade 2 lumber has more blemishes and knots than #1. But it is clear enough to pass as Premium or Select.

Further, the wood has a one-in-eight slope.

Grade #2 Structural lumber shows splitting up to 1½ times the board’s width and one hole every two inches. And the wood knots are no larger than 3½ inches.

This pressure treated lumber is ideal for lintels, framing, joists, rafters, trusses, beams, and fencing.

In addition, an SPF #2 2×8 spans distances of 14 to 11 inches, and in appearance grade, the wood boards are 66 percent clear wood.

  • #3 Grade Structural

This wood type has more splits, checks, well-spaced knots, holes, wane, and a grain slope of one in four.

It is also perfect for light framing and construction, packaging, shipping, and bracing.

Woodworkers use this lumber in projects where it is not visible. And it is at least 57 percent clear of defects.

Moreover, an SPF #3 2×8 spans distances of 12 to 4 inches.

  • Construction Grade

This grade primarily refers to #1-grade wood. Further, it works well for all residential construction, from trim to load bearing.

  • Standard Grade 

Standard grade wood features more knots and defects. Also, it is primarily a #2 structural lumber type.

You will find it in trusses, joists, and other load-bearing projects. And its appearance grading is 43 percent clear of defects.

  • Utility Grade 

Utility grade is #3 wood and has fewer defects and knot restrictions. However, it is not as strong as other lumber types.

Therefore, it is only used where it’s not visible and in light framing projects such as crates, pallets, and bracing.

Also, the lumber must be 29 percent clear of blemishes.

  • Appearance Grade

To grade wood, Mills and retailers use Select and Premium classifications and the wood’s transparency percentages.

But the appearance does not affect the lumber’s structural grade. It only makes the surface more appealing.

Nonetheless, the wood’s beauty makes it suitable for railings, deck boards, and other visible structural parts.

Pressure treated wood is commonly available as construction grade or #1 grade and #2.

This category is less likely to twist, warp, or cup and works best for railings and decking.

Premium and Select grades feature the best grain, appearance, and strength. But they are commonly reserved for special orders.

Moreover, most 5/4 decking is standard to mid-range grade somewhere between 1 and #2-grade lumber, or a combination of the two.

However, many lumber yards only have #2 construction grade pressure treated wood. So, you’ll need to pick and choose.

The wood will shrink more during drying if wet from the treatment bath. As a result, it will twist, warp, bow, and cup.

How Long Will Pressure Treated Wood Last In Concrete?

Pressure treated wood in concrete lasts up to 70 years or an entire century.

Besides, concrete provides a moisture-free environment and minimizes decaying and rotting possibilities.

In addition, the material is ideal for pressure treated poles and keeps them in good shape for longer.

You can also use the lumber type for wood foundations, which guarantees superior protection.

How Long Does Painted Pressure Treated Wood Last?

Depending on humidity and other environmental factors, painted Pressure treated wood lasts two to seven years.

Also, consider using a latex primer and water-based paint to guarantee a longer lifespan.

However, constant exposure to harsh weather conditions wears out the finish in a few years.

How Long Will Pressure Treated Wood Last In Water?

Pressure treated wood delivers a longer lifespan than untreated lumber.

Besides, it can last up to 30 years if in direct water contact. But ensure that there are no entry points into the lumber’s grain.

How Long Does Pressure Treated Wood Last Outside?

Pressure treated wood lasts 40 years when used in outdoor projects. Moreover, it is the standard lifespan for treated lumber.

However, ensure the wood has no cracks or water and moisture entry points. Otherwise, it will rot.

How Long Does It Take for Pressure Treated Wood to Rot?

Well maintained pressure treated lumber takes up to forty years before rotting.

But this duration lengthens or shortens depending on the type of wood, its climate, and climate.

However, pressure treated decks and flooring may only last ten years.

How to Maintain and Extend the Life of Pressure Treated Wood

Granted, proper pressure treated wood maintenance prolongs its lifespan. Besides, these practices help protect the lumber from naturally occurring issues.

The problems include shrinkage, mildew growth, swelling, and ultraviolet damage.

Also, maintenance practices protect all wood types, including underground, above the ground, and marine contact lumber.

They are as follows:

  • Step One

Start with cleaning the material with a mildewcide. Also, this step is suitable for new wood structures and keeps mildew from growing on the surface.

  • Step Two

Apply a water-repellent with an ultraviolet stabilizer. Choose the best finish for treated wood and keep water at bay.

This way, you will avoid wood shrinkage and swelling.

Also, the ultraviolet stabilizer slows down the lumber discoloration process.

  • Step Three

Carry out the above maintenance practices annually or every two years. You will guarantee a long-lasting pressure treated deck.

NB: Ensure the lumber is dry from cleaning before adding a sealer topcoat. Further, check how long the wood needs to dry.

Alternatively, sprinkle some water on the surface to test dryness.

If the wood absorbs the water, consider it a green light. Otherwise, wait another few days if it beads up on the wood.

Pressure treated wood has toxic chemicals. Thus, wear a dust mask and gloves when working.

Also, wash your hands after handling treated lumber. And avoid using the product indoors or on cutting boards to prepare food.

Causes of Rot In Pressure Treated Wood

Fungal issues are the primary reason for pressure treated wood rot. Further, fungi are tiny organisms moving and feeding on the lumber.

Hence, they cause the material to decay and soften, which eventually turns to rot.

Fungal spores usually affect wet lumber. And the fastest way to stop the damage is to keep the treated wood fry.

Unfortunately, dry wood is also susceptible to brown-rot fungi, which do not need much moisture to thrive.

Brown-rot fungus mainly affects birch wood and looks like brick-like cracking or an uneven pattern.

Generally, though, dry-treated lumber is less likely to rot. Besides, the rotting is easy to repair than wet, rotted treated wood.

Below is a detailed account of the causes of wood rot.

  • Water Damage

Water soaking into wood never ends well. Moreover, lumber with high moisture content is susceptible to rot.

Moisture also delivers a microorganism-friendly environment since they rarely grow in dry areas.

Although the pressure treatment seals the wood pores, bends and cracks can allow water into the lumber.

  • Chemicals Reactions

Pressure treated wood has chemicals to make it rot and insect resistant. And thus, the wood lasts longer.

However, these preservatives undergo chemical reactions with galvanic fasteners, causing galvanic rot.

It is challenging to detect or solve galvanic rotted lumber. Usually, you’ll need to replace the nails and screws.

  • Fungal and Microbial Infestation

Microorganisms, like builders and constructors, love lumber. Further, bacteria and fungi are the most famous culprits of microbial wood infestation.

These wood-eating organisms grow in damp locations, meaning wet lumber is a perfect habitat.

They multiply rapidly and constantly eat up the lumber. Eventually, the structure softens and decays.

Unfortunately, fungi spores are everywhere; the only controllable aspect is moisture around the wood.

So, always inspect the structure for suitable fungi growth spots. Also, keep the wood fry as the organisms do not grow well in such areas.

Use your hands to feel pressure-treated wood and check for any soft areas crumbling under pressure.

The supports and beams are most vulnerable to rot for treated wood decks.

In addition, the base of wood stairs and where treated wood trims meet can also be a fungi breeding area.

Hence, pay more attention to them.

Thankfully, you can preserve pressure treated wood or at least retard it to the lowest minimum.

Below are simple guidelines.

  • Use a Sealer

This product seals the lumber’s surface and provides an extra protection layer. Further, it includes stains, oils, sealants, paints, and varnishes.

These substances improve the deck’s durability and longevity. Even better, you will find formulas made for pressure treated wood.

Fortunately, the product is available at local wood hardware and is cheap. Therefore, you save money.

However, its protection is not absolute, requiring you to reapply the finish periodically.

In addition, some sealers need more frequent reapplication than others. For example, products protecting the wood from moisture need annual application. 

You can also get durable sealants but at a higher price.

Sealing the wood is a pretty straightforward venture. All you need to do is ensure that the material is dry for enhanced adhesion.

Sometimes, you may need to give the deck a few months to dry. But it will pay off, thanks to the resulting durable finish.

Moreover, use the sprinkle test to verify the material is dry for sealing.

Sprinkle some water on the lumber and observe how it behaves.

If the wood absorbs it, then it is dry. Otherwise, if water beads on the surface, wait some more.

Although some sealers work on damp lumber, allowing it to dry is essential for most formulas.

Use a brush to coat the pressure treated wood. Also, focus on the wood ends as they are more vulnerable to insects and moisture.

Some sealers need pressure spraying to deliver complete coverage. But ensure that the force is not too high lest you compromise the wood’s integrity.

Next, always brush out the wet layer after spraying.

Finally, sprinkle some water on the surface and observe how fast it soaks into the wood. If the process is quite fast, recoat the deck.

Here’s How to Seal Pressure Treated Wood:

  • Use Mildewcides

Preventing mildew from growing on the wood is prudent as they are a form of fungus. Besides, they cause wood rot and shorten its lifespan.

You can avoid these microorganisms by cleaning the lumber with a mildewcide or using commercial cleaners.

In addition, let pressure treated wood dry before coating after cleaning it with mildewcides.

  • Apply UV stabilizers

UV stabilizers make pressure treated wood resistant to harmful sunlight exposure. Besides, the wood is prone to sun damage, which causes discoloring.

Therefore, get coatings and finishes with UV stabilizers to keep the deck looking fresh and new.

  • Frequent Inspection

Frequent inspection is another way to keep pressure treated wood from rotting.

However, the exercise does not prevent the wood from rotting. It only lets you know where the wood is about to rot.

Also, it helps you know when to apply wood coatings and finishes for added protection.

Frequently Asked Questions

These questions include:

  • How Long Will Pressure-Treated Wood Last in Dirt?

Pressure treated wood can stay up to 40 years in dirt without rotting.

Further, preservatives used in treating the material keep it free from carpenter ants, termites, and fungi decay.

Therefore, the wood enjoys a long-life span.

  • What Are the Benefits of Pressure Treated Wood?

Pressure treated wood is an affordable alternative to naturally existing lumber.

Besides, the treatment provides superior protection against insects, mold, rot, and fungi.

Treated lumber comes from robust evergreen wood species, making it suitable for multiple building applications.

This wood weathers better than untreated lumber and does not discolor or gray over time.

In addition, you can stain or seal it to enhance its appearance and protection.

  • How Can I Use Pressure-Treated Wood

Treated lumber has many outdoor uses. You can even use it in some indoor locations where moisture is a concern.

Further, various pressure treated wood types come in handy in multiple residential, industrial, and commercial construction aspects.

They remain intact regardless of moisture or ground exposure.

The lumber is standard in household applications ranging from house trim, facia, and cedar shakes.

You can also utilize it for posts, siding, railings, decking, porches, and sheathing.

Moreover, most home fences, retaining walls, and garden boxes feature treated wood. And even wooden utility poles supplying power are pressure treated.

Bathrooms and basements are other projects where woodworkers use pressure treated lumber.

It keeps the structure safe from mildew, mold, and moisture damage.

In addition, some wood types undergo treatment to make them fire retardant.

Finally, other pressure treated wood uses include boathouses, boardwalks, gazebos, play structures, and docks.

  • What Is the Best Pressure Treated Wood for Ground Contact?

Pressure treated lumber for ground contact refers to stair stringers, wood foundations, deck railings, lumber yards, and fresh-water docks.

The wood also works for above-ground uses in tropical areas.

Treated wood for ground contact has a higher chemical retention level. Therefore, it repels agents supplying moisture in the structure.

The best pressure treated lumber for ground contact is wood grades labeled UC4A or UC4B. These tags mean that you can use the material underground.

However, ensure you seal prepare and seal the lumber before burying it.

White cedar is another option if you live in wet and swampy regions.

The wood is naturally rot- and moisture-resistant and guarantees a long-lasting project.

  • Is Pressure Treated Wood Water Resistant?

Pressure treated lumber is not water-resistant. Further, it does not have a waterproof surface.

The treatment makes the wood resistant to splitting, warping, and fungal decay, not water-repellent.

Therefore, consider sealing the surface using a penetrating oil or semi-transparent formula for complete water resistance.

Moreover, waterproof pressure treated wood with a non-emulsifying product in areas with high humidity, condensation, or continual ground moisture exposure.

  • What Happens If Pressure Treated Wood Gets Wet?

Pressure treated lumber becomes softer and susceptible to rot when wet. In addition, it does not have protection against rainwater.

Thus, it will start rotting when exposed to rain.

The wood’s recommended moisture level is below 15 percent, especially for kiln-dried lumber.

Also, this level should not exceed 17 percent. Otherwise, the wood will not be solid and safe enough for projects.

Lastly, waterproof the lumber before using it for outdoor applications.

  • How Long Do I Have to Wait to Waterproof Treated Wood?

Wait for about 30 days after the pressure treating process. This way, the preservatives infuse the lumber properly and deliver the expected protection.

Furthermore, rushing to apply the sealant may compromise absorption and the project’s quality.

Test the wood using the sprinkler method and confirm whether it’s ready for waterproofing.

The exercise involves sprinkling water drops on the lumber and observing the behavior.

If the water soaks into the wood, it is ready for waterproofing.

On the other hand, the wood is not ready for sealing if you observe bubbles.

  • Do I Need to Seal Pressure-Treated Wood?

It is advisable to seal pressure treated lumber. Further, consider reapplying the finish annually for optimal protection.

In addition, the process fortifies the wood against moisture and gives it a lovely appearance throughout.

However, always consult your dealer as premium quality pressure treated lumber comes with in-built sealers.

The wood lasts several years without maintenance.

  • Are There Pressure Treated Softwoods?

Generally, the available softwood types in various geographical locations determine the species used for pressure treatment.

For example, Southern Yellow Pine (SYP) is robust and available in the eastern U.S, while a spruce, pine, and fir mixture (SPF) dominate the northern U.S.

Fir, Douglas fir, and hemlock are typical in the western U.S. and Canada.

Also, Douglas fir ranks the strongest, whereas hemlock and fir are slightly more potent than SFP.

  • How Do I Dispose of Pressure Treated Wood?

Pressure treatment involves infusing preservatives into lumber at high pressure. The process prevents wood decay and increases its lifespan.

However, as with all treated chemical substances, please be careful when disposing of treated wood. 

Furthermore, do not burn the wood. The process heats chemicals in the lumber and releases them into the atmosphere.

Also, you need protective clothing when working with treated wood. Get a dust mask and hand gloves, and work in a well-ventilated area.

  • What Are the Precautions When Handling Treated Wood?

There is no primary difference between handling treated and untreated wood. So, always wear safety gear.

Gloves protect your hands from slivers and water-soluble preservatives. Moreover, wash your hands thoroughly before eating or drinking.

Although residential pressure treated wood is safe for use, dust and particles are harmful with prolonged exposure.

Wear a safety shield or goggles to protect the eyes from debris and dust.

Also, get a dust mask when cutting, drilling, or sanding the wood to avoid inhaling the chemicals.


Pressure treated wood’s lifespan depends on the lumber type, climatic and weather conditions, and maintenance practices.

So, it is prudent to learn more about the material to clarify any concerns:

How Long Does Pressure Treated Wood Last?

Pressure treated lumber has a longer lifespan than untreated wood. Besides, it can stay up to 40 years without decaying or rotting.

In addition, you can add an extra protection coat to decks and other outdoor structures to increase their longevity.

Image of a woodworker wearing hearing protectors for woodworking

Tyron Otieno

Tyron is an avid woodworker and writer. He founded this website to help other woodworkers, whether hobbyists or professionals by sharing his knowledge and experiencie after a decade of woodworking.

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