16 Pros & Cons of 5/4 treated Decking Plus Things to Consider

The first deck I ever built had pressure treated decking. Since then, I have used many different types of decking material. Composite, PVC and cedar, all great decking material but treated 5/4″ always returns as a decking option. For many different reasons, which leads us to this article. What are the pros and cons of 5/4 treated decking? Why would you want to use treated decking? Why would you not want to have 5/4″ treated decking on your next deck?

Pros of Treated Decking

  • Economical
  • Fungal Resistance
  • Insect Resistance
  • Durability
  • Stability
  • Workability
  • Versatility
  • Easily repaired

Cons of Treated Decking

  • Checking and splinters
  • Warping and Shrinkage
  • Hot under bare feet
  • Fading
  • Requires Maintenance
  • Not moisture resistant
  • Environmentally harmful

First, before going into the details of treated decking, let’s confirm some definitions. Pressure-treated decking is surfaced infused with chemicals to prevent fungi and insect damage.

“Pressure-treated lumber is wood that has been immersed in a liquid preservative and placed in a pressure chamber. The chamber forces the chemical into the wood fibers.”

How Stuff Works 

In short, you can treat your decking at home, but “pressure treated” needs to be done in a factory were pressure chambers can push the chemicals into the wood deeper than home application. Most treated decking is treated with alkaline copper quat (ACQ) or Micronized Copper Azole (MCA). Copper is toxic to many wood damaging fungi and insects.

This is why we treat our decking, for fungi and insects will not destroy the decking helping it last many times longer than untreated wood.

 “ACQ binds to wood fibers very well and allows wood to last decades even when it is in contact with the ground.”

How Stuff Works 

One more feature to clarify. The first pressure treatedOpens in a new tab. deck I built was not 5/4″ decking. It was what use to be the standard, treated 2×6 decking. Three of the key differences between 2×6 and 5/4″ decking are depth, profile and cost.

A milled 2×6 is 1 ½” (38mm) thick where 5/4 decking is 1″ (25mm). The impact on your deck is 5/4 decking can only span 16″ (400mm), not 24″ (600mm) as traditional 2×6 decking. Requiring additional joists, but the reduced spacing allows for longer joist spans. I have written a more in-depth article about deck joist if you want to learn more. Click hereOpens in a new tab. to read more about deck joists.

One of the advantages of 5/4 decking compared to 2×6 decking is the rounded edges. Traditional 2×6 boards have square edges. 5/4 decking has rounded edges, which reduces water pooling while minimizes edge splinters on the decking. The small round over also increases the visual appeal of the decking gapping. I have installed a lot of laminate flooring. One of the innovations I loved was the V-grooved boards as they blended the boards together better visually. The same is true with radius edge 5/4 decking boards.

Finally, this reduction in material reduces the cost of the decking. 2×6 boards have always been an economical decking option, but 5/4 decking reduces decking costs one more step. 5/4 decking cost roughly three quarters the price of 2×6 decking, which brings us to our first advantage of 5/4 treated decking.

Pros of Treated 5/4 Decking

With the first three, I will repeat myself a little from defining treated decking, but we will get into more specific advantages of 5/4 treated decking as we progress.


If the deck budget is tight, there are few decking that will cost less than 5/4 treated decking. Seasonally affects wood decking price considerable but expect to pay around $2 a square foot for 5/4 decking. Considerably less than any composite decking or even the next level up cedarOpens in a new tab. decking. 5/4″ decking is the most affordable decking option.

There is a large range of what you pay for decking. I have written a fuller article comparing wood, composite and PVC deckingOpens in a new tab. cost. Click hereOpens in a new tab. to read more about decking costs. But 5/4 decking is the clear winner.

Fungal Resistance

Wood will naturally deteriorate and be broken down by fungi. All part of the cycle of life. Untreated wood will last roughly 5-7 years outside, where treated decking should last about 15 to 20 years and even more with proper maintenance. But we will look at that more under cons of 5/4 decking.

Insect Resistance

Along with fungi, termites and other wood-boring insects will destroy your decking if untreated. 5/4 decking treated with cooper prevents both fungi and insect damage of your decking, which is essential in warmer climates like Florida. The warmth is great for decks but also for termites. Treated decking prevents insect damage.


Spruce, Pine or Fir, the usual wood treated for 5/4 decking are a durable material.

(Sitka Spruce) “Janka Hardness: 510 lbf (2,270 N)”

Wood DateBaseOpens in a new tab.

Not all 5/4 treated decking is Spruce, but this gives you a rough idea of firmness and durability. Janke hardness is a test of how much pressure it takes to embedded 0.444″ (11.28 mm) diameter steel ball into the wood to halfway. Get a rock on your shoe, and it will take rough 500lbs to push that into the decking. Which when focussed on a small stone is less then you think but still a sturdy decking.

It can still be scratched, but it takes more. An excellent durable decking against dog claws, scratching the decking.


5/4 treated decking will shrink as it dries out, but expansion and contraction are minimal. For PVC decking, you often have to allow for ¼” (6mm) expansion and contraction through the heat of the summer.  Limiting installation and design to allow for movement. Treated decking has a high level of stability. Making it easier to work with.

Easy to work with

Basic power and hand wood tools you can work with treated decking. Yes, there are more specialized tools that will improve efficiency and deck appearance. But with basic skills, knowledge and tools, you can install 5/4 decking. If I was going to recommend any decking for a first-time deck builder or DIY, 5/4 decking is it.

Versatile in application

Decking, picture frame, vertical skirting, privacy wall, there are so many ways that 5/4 pressure-treated deckingOpens in a new tab. can be used. It is a very versatile material. Having a structural strength, it can be used in many ways that composite material cannot. If you can imagine it and screw it, you can probably use 5/4 decking for it on your deck.

Being a solid product, you can cut, mill or rip down to any size that works for your project. One limiting factor is the rounded over edge. Ideally, all edges for the decking should be rounded off. But if you need to rip down a decking board, it can be rounded off with a router to match the profile.

5/4 treated decking can be Easily Repaired

Scratches can be sanded out and stained to match the rest of the deckingOpens in a new tab.. Being readily available damaged decking boards can be easily replaced as new boards are similar enough to previous years as to match. Unlike composite decking, with often discontinued product lines every few years preventing sourcing new boards later.

Now for the other side, what are the cons of 5/4 treated decking?

Cons of 5/4 Treated Decking

Being neither a natural product nor a synthetic treated decking has some serious flaws. Most are related to either; it is natural, economical wood or treatment. 5/4 treated decking is not the best of both worlds but rather an economical solution for decking

Checking and splinters

5/4 decking needs to be regularly sanded, saving your feet from slivers. End board screws can also split the wood as it shrinks around the screw.  Damaging the end of the decking. A good practice is to predrill all end screws and overhang the decking a 1 ½” (38mm) to provide additional material around the screw holding the decking together.

Treated decking can also check, creating long unsightly cracks along the deck board. This can be minimized with regular staining to protect the wood, but we will get to that later.

Warping and shrinking

Pressure-treated wood is prone to warping and shrinking due to its uneven water content level. Lacking a stabilizing core because of its thinness, it will warp more readily than other decking material. Proper screwing can minimize this, but care still must be taken to protect the decking during the building process.

Treated decking may be seasonal stable but will shrink after installation. It should be installed fairly tight because it will quickly shrink, enlarging gaps between boards.

Hot under bare feet

Not The hottest decking out there, but treated wood gets pretty toasty in the sun. If you love to stroll out on your deck in the sun, 5/4 treated decking is not for you, unless you like to do the silly hot feet chicken dance.

Jim Finlay did a comparison test of decking in the sun. Treated decking became 47°F (26°C) hotter in the sun. Raising the temperature from 80°F (27°C) to 127°F (53°C) on the surface of the decking. It is not unusual for a surface temperature to get hotter than the air temperature, but treated decking is no exception. Cooler than composite and PVC deckingOpens in a new tab. but still pretty hot. To read the full study, click here.Opens in a new tab.

Limiting stain colours options

Legend has it that Henry Ford said you could have the Model T in any colour you want as long as its black. Pressure-treated decking also is limited in staining options. The brown colour of the decking limits your options of decking stains as all stain colours must work off the light brown colour boards. Often you are better of just embracing it and clear coat or choose a similar brown colour stain.

Deck Fading

Cedar decking “greys” if not stained. Often an appreciated rustic deck look. Treated decking will lighten in colour but not in an enhancing way. When installed, it will have a rich deep brown look, but over time, it will become a faded brown. Requiring staining to refresh its colour.

Requires Maintenance

5/4 treated decking is the least maintenance free decking out there. The decking needs to be seal or stained within a year of installation. Then regular cleaning and staining are required for the deckingOpens in a new tab. to last.

The regular cost of maintenance will quickly eat up any savings in the initial decking cost. Most estimates put 10 years as the break-even point. That if you regularly stain the decking as required by the tenth year, you will have spent as much money hiring someone to sand and stain the decking as if you had paid for low maintenance composite decking, which will last at least another 15 years. Quality stain will minimize the frequency, but additional work and cost must be included with treated decking.

Not moisture resistant

Treated decking is treated for insects and fungi, not water, which means treated decking to last needs to be sealed, regularly. In a dry climate with sufficient deck ventilationOpens in a new tab., the decking may dry out after a rain, but the wood still can become soaked and rot out. Sealing a wood deck to minimize waterlogging is a required part of its maintenance.

Environmentally harmful

Fungi are part of a healthy ecosystem, which decking is treated against. The chemical used can be damaging to the environment, less than they use to be but still damaging.

There is some debate on the level of harm that copper treatment is on the environment. I have read that cooper is natural and is actually required in a healthy econ system. I guess the conversation is about level. But when considering treated wood, we cannot ignore that is has an environmental impact. How much is a much bigger conversation then for here.

Also, disposal of treated decking becomes a problem. It is treated as not to decompose as nature intended. Slowing the process as it sits in the landfill for 13 years or more after use.

“There have been government studies that show toxicity in the smoke and ash. The ash must be properly disposed of due to the high toxicity within it and the smoke must be contained as to not affect the air.”

Civil EngineersOpens in a new tab.

Because of the chemicals in treated decking, it should never be burnt, limiting the disposal of the decking after use. It can’t be burned; it can’t be mulched. The only thing left is to fill the landfill with it.

Five Things to Consider about 5/4 Treated Decking

These are not necessarily pros or cons but are an important part of the discussion when considering 5/4 treated decking.

Longevity of 5/4 decking

Is 5/4 decking temporary or lifetime decking? The answer is maintenance, determining if its lifespan is 20 years or 60. Treated decking will last as long as its cared for, or close to it.  

“Wooden decks have a life expectancy of 20 years according to Citi Bank and the National Home Builders Association (NHBA). If decks were built and maintained properly, their life expectancy should be double or triple this figure.”

Mississippi State University  

One of the ways to increase treated deck life, according to Mississippi University, is end treatment of all cut boards during construction. Whenever you cut treated wood, it should be resealed either by painting on end treatment with a brush, spraying or soaking in a bucket. The factory preservative is only surface deep. Without end treatment, the core of the decking is unprotected and will rot.

Maintenance will increase decking lifespan but not heal. If treated decking is allowed to deteriorate, there is no recovery. You can slow the process by staining, but it will not recover after weathering from the sun or rain. Treated decking must be maintained from day one to last.

Required pressure treated decking fasteners

Cooper treatment is excellent if preventing fungi and insect damage but is corrosive on metal. All fasteners and hardware in contact with the decking must be zinc or Polymer-coated steel screws or stainless steel. Untreated fasteners will corrode faster than the decking. Causing decking failure as the decking boards come loose from the joist. Always check that the fasteners are compatible with pressure-treated wood.

The good news is polymer-coated screws are economical and often are colour matched for decking. Helping to hide the screw heads.

5/4 decking is not treated for ground contact

Rarely this will be an issue as the decking will be raised from the ground by the joist. Ground contact is defined as 6″ (150mm) ground separation. Decking must be raised at least that high of the ground.

Also, it’s essential that air circulates under the decking to allow the underside to dry. The underside of decking cannot be sealed or stained after construction, so drying naturally with air circulation is critical.

Myths about Toxicity of Treated Decking

I remember when you would get a sliver of treated wood, it would fester and puss up and hurt like a bugger. It just felt like it was not good for you. That walking barefoot on a treated deck could have potential health risks. This was primarily due to the Chromated copper arsenate (CCA) that wood was treated with. In particular, the arsenate element, which has led the industry to reach a voluntary decision in 2003.

“Effective December 31, 2003, CCA manufacturers voluntarily canceled residential uses of CCA”

Iowa State UniversityOpens in a new tab.

Which is why residential decking is now treated with ACQ or MCA, which has also been tested with excellent results. A research paper titled “Human Health Risk Evaluation of ACQ-Treated Wood” By Cushing, C A Golden, R; Lowney, Y W; Holm, S E after studies found that ACQ-treated wood poses no health risk from exposure from treated decking.

“exposures to ACQ-treated wood do not result in concentrations high enough to be associated with acute effects…ACQ Type D from the surface of treated wood are not expected to be associated with any adverse effects to adults or children who might come into contact with this product.”

Walter ReevesOpens in a new tab.

In conclusion of treated decking toxicity. Research has proven that there is no risk for you or your toddler crawling on the deck. The levels of copper are high enough to prevent fungi and insects but not high enough to be toxic to humans. Even little children crawling on treated decking poses limit health risk.

Conclusion of Pros and Cons of 5/4 treated decking

5/4 treated decking is economical, preserved to last and easy to work with, but it does need to be maintained. Treated decking also has an environmental impact due to its treatment but has been minimized with recent improvements in treatment methods.

If you are looking for a simple, budget deck, 5/4 treated decking is an excellent choice. It will not break the bank. It is easy and versatile to work with. You can enjoy your deck at a reasonable price, but just plan that every few years you will seal or stain it, to keep it vibrant and beautiful.

Ryan Nickel

A Red Seal carpenter, passionate about building decks to be enjoyed.

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