What Is the Recommended Joist Spacing for Trex Decking? Best Guide to Trex Deck Installation

Image of a trex decking so What Is the Recommended Joist Spacing for Trex Decking?As an art, woodworking has always been the source of elegance in most home designs. Apart from using standard wood in making decks, woodworkers have advanced to use durable and strong wood products such as composite, vinyl, and Trex decking. What’s best about Trex decking is how it’s 95% recycled materials. But What Is the Recommended Joist Spacing for Trex Decking?

For Trex decking, it would be nice if you would go for a 16″ OC joist space. Doing this will ensure that you don’t have a saggy or uneven surface on your decking.

What to remember is that you should use your Trex decking for the intended purpose. Some of the common uses include walking surfaces, fencing, guardrail systems, and trim.

Table of Contents

Can You Put Composite Decking on Wooden Joists?

Yes, composite decking is ideal for wooden joists, especially when you are working on your decking. Even so, ensure you go for the pressure-treated joists for durability purposes. Also, work on a strong foundation that can withstand the deck’s weight.

The joists will act as the base where you’ll lay and attach the decks.

How to Install Composite Decking

Composite deckings have undeniable advantages. Therefore, you need to ensure you correctly install them for the best results.

Here are the quick steps you need.

Step 1: Plan and design

Before building your deck, ensure you have a solid decision on where you want to place it. Besides, check on the needed materials, then gather all the necessary tools. 

Tip: If your deck is in direct sunlight, don’t go for a darker composite material since it’s good at retaining heat and will eventually get too hot to walk on.

The best decision will be to go for a lighter color or a mixture of colors.

Step 2: Measure and Pour

Before setting up your foundation, do some measurements on your plan to install your composite decking. 

You can start by digging holes for your deck footings. Then, I suggest you use a post-hole digger for more precise holes. After this, pour some concrete and give it approximately 24 hours to dry.

Step 3: Frame

As you are waiting for the concrete to fully dry, secure your deck to the house by installing a ledger board.

After this, it’s time to attach the post anchors to the deck footings. You can also attach the stirrups but ensure the concrete has fully cured.

The other option is to cast post anchors into the concrete before it dries. For this case, the ideal item to use is the KlevaKlip since it will help you get a perfectly aligned deck. It’s also best for fine-tuning. If you are using posts or bearers, this is the right time to attach them to the stirrups.

The next thing is to frame your deck depending on your deck size, then add the concrete footings. 

Installing the joist hangers is straightforward. You only need to ensure you do the installment on both the end of the beam and on the ledger. Do this at intervals of 15.24 cm apart. 

It’s now time to mount the joist boards. Before this, start by cutting them into the desired sizes, then seat them into the hangers. Finally, secure them with nails.

Tip: When working on your deck, ensure you keep checking on the level and adjust when necessary. Also, don’t forget to keep plumbing.

Step 4: Secure

While securing your deck, ensure it’s correctly leveled. You can do this using a chalk line to find the highest spots.

If you realize any points that seem to be at high risk of moisture, ensure you properly seal them to prevent the growth of molds, mildew, and other fungi.

You can do this using a GTape joist protector to cover such areas. Also, it’s good to use a dark tape color.

Step 5: Lay

If you make it to this step, it means that you now have your foundation stable and in place. After this, it’s time to lay down your deck boards. You can do this using the manufacturer’s proprietary fixing system. 

Tip: You should note that you’ll have to employ different fixing methods, including biscuit type, strip click-in, or top fixing screws that disappear through the surface.

Also, it’s not recommended to use butt joints on composite decking due to the significant thermal movement. 

Here are other tips for properly installing composite decking joists.

  • Support the joists with blocking.
  • Ensure your joists are well leveled.
  • Check for any protruding nails and screws.

Here’s a video on how to install a composite decking:

Does Trex Decking Need to be Spaced?

Yes, you’ll need to gap your Trex decking both end to end and width to width. The gaping will prevent your deck from cracking or splitting if there is a slight thermal contraction or expansion.

Even more, you’ll realize that gapping your Trex decking will be essential, especially for drainage purposes. It also provides room for shrinkage of the joist system.

Tip: You’ll need some openings under the decking to improve the airflow. Alternatively, you can consider increasing the gapping to about 10mm.

What is The Recommended Gapping for Trex Decking

The gapping on Trex decking depends on the temperature conditions of where you intend to place it. For instance, the width to width gap requires a 6mm gap for temperatures above 4.5 degrees and a 10mm gap below 4.5 degrees.

On the other hand, the end to width side will require a gapping of at least 3mm for temperatures above 4.5 degrees and 5mm for temperatures below 4.5 degrees. 

Finally, if you decide to use an Abutting gap, the recommended gapping for temperature above 4.5 degrees will be 6mm and 13mm for the one below 4.5 degrees. 

You should note that the above gapings are as per the surrounding temperature. Therefore, the recommended joist spacing on Trex decking is 16 inches OC.

Should You Predrill Trex?

Pre-drilling has always been necessary for most woodworking applications, and Trex decking is not an exception. It helps to prevent splitting the end of the boards. But, with the advancement in fastener technology, you can escape the predrilling stage.

What is the Difference Between Trex and Composite Decking?

Trex is still a composite material even though it contains plastic.

Therefore, if you decide to go for Trex, you’ll still get that elegant look of outstanding wood with the durability of a composite. 

Does Trex Decking Get Hot?

By the rule of the thumb, any surface exposed to scorching sunlight will get hot. However, Trex decking does not get that hot as pressure-treated wood does. 

If you want to reduce the hotness on your Trex decking, consider using lighter colored boards since they will be slightly cooler than the darker ones.

Can You Install Trex Over Existing Deck?

Yes, you can do this but ensure you adhere to the necessary precautions. For instance, if your deck has warped, it means that the same has happened to the joists. In such cases, you’ll want to replace either a joist or two.

Alternatively, consider attaching your composite decking boards to the joists. Doing this will be easy with 3” deck screws. 

Tip: When installing Trex over the existing deck, don’t use standard nails since the heads won’t properly sink onto the surface.

Is a Special Blade Necessary When Cutting a Composite Decking?

Here, you’ll want to be specific since not all blades designed for wood will properly cut Trex or similar composite decking material. 

For the best results, it would be best if you did the cutting with a finer tooth blade. The reason is that you’ll find some composites made from a combination of PVC and wood while others are from PVC alone.

What Is the Blade for Cutting Trex?

I recommend using the Modified Triple Chip Grind (MTCG) since it prevents the material from getting hot while cutting, thus allowing for melt-free cuts.

You can also go for TiCo high-density Carbide as it offers increased performance on Trex branded materials, cellular PVC, and composite decking.

What Are the Problems With Composite Decking?

Composite decking is rapidly taking over from standard wood decking. Although the product comes with many advantages, especially in durability and beauty, this product also has some disadvantages.

Here are some of the problems you need to pay attention to when using composite decking.

  • Warping and Weakening

Yes! Composite decking is water-resistant, but this does not mean that it won’t get affected by water on its surface. 

If your deck is constantly exposed to moisture, you’ll realize some effects such as shrinking, warping, shifting, swelling, and many more. 

All these are caused by the composite nature of the deck that lets it be more sensitive to humidity, temperature, and sun exposure.

Therefore, you can’t be very sure of the water resistivity on composite deckings, even for those within boards on the same deck.

  • Staining and Color Fading

What will attract you first when choosing a composite decking is the colors. The other best thing about these products is how they require low maintenance with less surface treatment. 

Altogether, this does not mean that your deck is safe from fading, especially if exposed to direct sunlight.

Your composite decking is also prone to easily staining from common things such as a spill of wine, fallen leaves, among others.

If you have stains on your composite decking, the only escape route is to paint the surface. For this reason, most manufacturers opt to give a matching paint. But this is not what you needed when you chose the composite decking. Hence you’ll be sure of some disappointments.

  • Moisture Resistance Does Not Stop Mold.

Even though this material is known for its water resistance, it doesn’t mean that you have fully escaped the issue with mold growth. 

What will mostly cause moisture to penetrate your deck is the texture of the surface and the rough surface on the uncapped ends. 

With a waterproof surface, the water may not get absorbed. In such a scenario, it becomes stagnant hence causing mold growth. It even becomes worse if you live in areas with high humidity.

  • Composite’s Characteristics Limit Usability

Some natural attributes of the composite deckings limit usability, and normally it’s hard to avoid them. For instance, a wet composite surface is not safe, especially on pool sides. The reason is that the material has a composition of oil-based plastic. Thus, it doesn’t absorb water as wood does hence leaving a slippery surface.

You’ll also experience some limited usability, especially on sunny days since this material is good at retaining heat, making it hot to bare feet.

Another problem is that composite decking has less strength compared to solid wood. With this characteristic, you’ll require smaller joist spacing during construction to prevent sagging.

  • Easily Scratched Surfaces Can’t be Fixed.

What gives the composite decking a soft texture is that it contains more plastic than wood fiber. With such a surface, you’ll realize that sanding is not an option as in wood. The only best solution is to replace the board completely.

Other problems with the composite decking include.

  • They aren’t natural.
  • The deckings are not completely maintenance-free.
  • It’s more expensive than wood.
  • It’s heavier than natural wood.
  • You can accidentally melt your deck.
  • The installation cost is a bit high.

Pros of Composite Decking

  • They come in a variety of colors.
  • You can recycle the materials.
  • The technology is improving.
  • There’s less maintenance.
  • It’s environmentally friendly.

Do You Need Special Screws for Trex Decking?

Yes, you’ll want to be very keen on the types of screws you use. For instance, if you come from an area close to saltwater bodies, consider using the recommended stainless steel screws.

Here is some additional information on the use of screws on Trex.

  • Use two screws per joist.
  • Do not countersink the recommended screws since they are designed to install flush with the surface.
  • You can use the 2¾” or 3” screws with Trex 2 x 6 product.
  • It’s easy to route all decking products following the provided instructions since you can use all of them with Trex Hideaway Hidden Fasteners.

Can You Screw Down Composite Decking?

Even though this method is outdated, many people still use it. Even better, it’s the cheapest and easiest way of installing composite deck screws.

Things to Consider before Using Screws on your Composite Decking

  • The type of screw to use depends on your project’s requirement.
  • You must not screw on a hollow wooden decking since the screws won’t permanently fit.
  • Most composites are prone to splitting. Hence don’t use large screws on them to avoid a lasting impression.
  • Screw heads will remain on your deck’s surface. Therefore, you can consider going for a seamless and smooth design.
  • Screws can sometimes loosen up due to expansion and contraction.
  • Since most composite decking materials are dense, installing them using screws can sometimes be difficult.

Which is better for a New Composite Deck, a Fastener, or a Screw Deck?

Yes! This question sounds so straightforward. However, you may find it difficult to decide on the ideal fastener for your new deck. 

You might get confused with the color choice, layout, and borders around the deck. 

Here is the breakdown of the fasteners and screws for your new composite deck.

  • Color Match Composite Deck Screws

For the best results, choose color-match deck screws that offer premium performance. Such screws include:

  • The deep recessed with a star drive head that can prevent cam-out.
  • Type 99 slash point, acute threading, tri-lobular to allow them to penetrate dense boards easily.
  • Reverse threading screws to help prevent surface imperfections and mushrooming.

The above screws come as stainless steel and epoxy-coated steel. You’ll mainly use them on fluted profile, full profile, or square edge boards.


  • EverClip Hidden Fasteners

What’s best about this type is how it provides a seamless finish ideal for barefoot. Some of its additional benefits include:

  • Consistent board spacing across the deck.
  • Ample holding power facilitated by the serrated edges on the clip.
  • The item provides a seamless finish with no visible fasteners.
  • Installation is straightfoward with included pre-assembled clips.

Do I Need to Pre-drill Composite Deck Screws?

Though it’s not a must to predrill on composite deck screw, you might want to consider doing this if you have solid composite decking. But you should not screw or drill through a hollow composite deck. 

Also, you may pause the risk of splitting your board when driving the screws. Thus, it’s not necessary to predrill before screwing.

Tip: The 3” decking screws are the ideal choice for your composite decking since they securely sink a good distance into the joists and never back out like nails.

Can You Use a Staple Gun On Composite Decking?

Did you know you can work with your composite decking the same way you do with timber? Now you know, but the one thing you’ll want to avoid is using a nail gun on it.

How to Install Decking without having to Pre-drill

  • Use Camo screws.
  • Overhang the decking to minimize predrilling.
  • Add blocking for decking butt joints.
  • Consider using longer decking boards and transitions.
  • Backspin screws instead of predrilling the boards.
  • Use the recommended deck screw size.
  • Go for Hillman power pro deck screws.

The Dos and Don’ts When Installing Composite Decking

  • Consider using the right tool for the job.
  • Leave some expansion gaps.
  • Don’t cut the boards at different times of the day.
  • Leave some adequate ground clearance.

Can You Put Screws in Trex?

Yes, you can use screws on Trex. The best part is how they have a stronger holding power than nails.

Why is My Composite Deck Warping?

Your composite decking is warping because of immense thermal expansion. As discussed early, the composite decking has a composition of plastic fiber and wood.

With the sun above, the plastic fiber gets heated and expands. Unfortunately, the fibers will only return to their original size if your decking has some gapping.

How to Fix a Warped Composite Decking

Do you know why many woodworkers prefer composite decking to wooden decks? Well, the main reason is due to the warping problem. Even so, composite decking also under-go warping, and here is how you can fix your warped decking.

Note: For most warped composite decking, you’ll need to replace the individual pieces, and here is the easiest way to do it.

  • Step 1

Your first step is to check for the boards that need replacement, after which you can take the measurements of the boards that you’ll use for replacement. 

Ensure that you are so precise, especially when dealing with already cut boards. Also, don’t forget to check on the depth of the decking boards.

  • Step 2

It would be best to have a circular saw in this step since it’s ideal for cutting through the warped decking board. 

Ensure you follow all the safety precautions and don’t cut deeper than the depth of the decking board to avoid damaging the joists.

  • Step 3


Here, you’ll want to use a crowbar to remove the already cut warped decking out of the frame. 

  • Step 4

It’s now time to get rid of any screws that you had used before. Doing this is easy using a screw gun.

  • Step 5

Finally, you can now replace the warped deck with the new one. Ensure it’s of the same size, color, and material as the original one. 

Is a Composite Deck Worth the Money?

Yes, this product is worth spending an extra cost. It might seem expensive on the first purchase, but its durability is unparalleled to the ordinary wooden deck.

With this product, you’ll enjoy less maintenance, thus cutting the cost of purchasing the maintenance tools. 

How to Waterproof Composite Decking Boards

There are several ways which you can use to waterproof your composite decking. Here are some:

  • Under Deck Ceilings System

You can waterproof your composite decking by attaching an under-deck ceiling system. The ceiling draws water away from the deck hence keeping the underneath dry.

You’ll realize that the ceiling system utilizes aluminum panels or vinyl to draw water away. Despite this, the system also has some drawbacks, including damaging the wooden joist.  

Such happens when the ceiling allows water to drip on the joist, which will eventually cause rot.

  • Interlocking the Decking Systems

If option one didn’t work for you, you could choose to use this method. But you should ensure you leave no gap between the system and the house to eliminate any room for water damage.

  • Composite Decking Flanges

Most composite deckings come with gaps between them. Such spaces allow for easy water flow. If you want to waterproof this area, consider using rubber flanges to fill the gaps.

  • Roof Deck Sleepers

Using the roof deck sleepers is another best option for waterproofing your decking. You only need to raise the deck above the ground to prevent water from building up beneath the deck. 

Doing this is as easy as using waterproof wood to raise the deck. With the raised deck, air will freely circulate underneath, preventing the area from getting moisturized.

Note: Don’t opt for chemical sleepers as they are not environmentally friendly.

  • Under Deck Drainage System

If you prefer this method, then you’ll have to install a waterproof gutter system below the composite decking right above the deck joist. 

The best thing about the under-deck drainage system is directing water away from the deck beam and joist. With this capability, the wooden joist will not absorb water, and the deck’s underside will remain dry.

Which is Better Vinyl or Composite Decking?

Before deciding which is best between the two, let’s check on some of their pros and cons.

Composite Decking 


  • It looks similar to real wood.
  • You don’t need to repaint or stain.
  • Long lifespan.


  • Deck boards can easily get scratched or chipped accidentally.
  • The colors might fade from the sun.

Vinyl Decking


  • Elegant, upscale look.
  • No need to repaint or stain.
  • It’s durable and backed by a long-life warranty.
  • The product doesn’t rot or grow mold.
  • Resistant to color fading.
  • It’s completely water-resistant.


  • It’s a bit expensive.

I would recommend vinyl decking from the above pros and cons since it’s more adaptable to most weather conditions. Hence it has enhanced durability and elegance. 

Even so, it would help if you went for the one that suits your budget and project requirements.

Final Thoughts

Up to this point of the article, you have seen how Trex decking is ideal for your decking projects. You only need to ensure that you follow the correct installation process to avoid the common problems associated with this product. One of the major steps in the installation process is joist spacing. So…

What Is the Recommended Joist Spacing for Trex Decking?

I would recommend 16” OC since it allows enough space between the boards for efficient thermal expansion while avoiding sagging.

Thank you for reading this article to this point. If you have any other questions related to the topic, kindly post them in the comment section below. You can also include your observations. Thanks once again.

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.