4 Common Composite Decking Installation Mistakes

Last Updated on June 4, 2024 by SampleBoard

A Guide for Homeowners

Unlike traditional pressure-treated wood deck boards, composite decking has a longer lifespan, mainly when correctly installed.

It won't split or crack and is designed to resist severe weather conditions.

The boards' composite material can bear high UV exposure levels without fading and are resistant to mold in wet weather conditions. 

When properly installed, composite decking requires less maintenance and provides a sturdy and reliable outdoor space for you to enjoy.

While mishaps can occur during installation, understanding and avoiding these common mistakes can empower you to ensure the structure's strength, safety, and longevity.

Image credit: nikkisplate.com

4 Common Installation Mistakes To Avoid

1. Incorrect joist spacing

Proper joist spacing is vital for the sturdiness and reliability of your composite decking.

Since joists provide the support your deck boards need to ensure the structure's weight is evenly distributed while ensuring your deck stays structurally sound and safe, it's imperative to ensure correct installation. 

The composite decking boards can sag when joists are positioned too far apart. The decking surface will also be uneven if the joists aren't a different height. 

To avoid these issues, it's essential to ensure correct joist spacing. The proper joist spacing for composite decking varies from one deck to another based on its:

  • Weight
  • Size
  • Shape

Many composite decking manufacturers/ suppliers have directions on joist spacing length.

So, remember to ask for these guidelines when you buy a deck to ensure correct joist spacing and your structure's strength and durability.

To ensure correct joist spacing, you can use a joist spacing tool or measure the distance between each joist with a tape measure, ensuring it matches the manufacturer's recommendations.

Image credit: Pinterest

2. Not ensuring adequate ventilation beneath your decking

Composite decking materials are semi-organic, absorbing small amounts of water and moisture.

Over time, dampness underneath your deck can cause structural issues and mold growth.

As the excess moisture passes into the decking boards, your decking may contract and expand, leading to warping, cracking, and other forms of damage.

Consider ventilating the deck's underside to ensure sufficient air circulation under the decking. This will enable the material to dry sooner and prevent these issues.

Adequate ground clearance also allows proper drainage under your composite decking. 

This ensures water flows away from your structure, minimizing the possibility of water pooling and damaging your decking materials.

Image credit: Pinterest

3. Failure to use double joists where deck boards meet

Laying your composite decking requires a sturdy substructure.

Failure to use double joists where boards on the deck surface meet can cause them to slip or split, compromising safety.

The double joist technique involves installing two joists to create a more stable and robust framing for your composite decking.

It includes spacing these two joists closer and securing the composite decking boards on both. This offers extra support and reduces the risk of warping or sagging over time.

Image credit: yardzen.com

4. Opting for low-quality subframe material

Your subframe material choices will determine your decking's durability and how it performs.

Using low-quality or subpar materials for your subframe means your composite deck will only last for a while.

While wooden subframes are a standard option for most homeowners, they're susceptible to rot, decay, and termite infestation.

When water or moisture soaks through your wooden subframe, it becomes weak and unstable. It can also contract and expand and will likely split or twist.

As wooden subframes weather, their sizes change. They expand when wet and contract once they dry out, resulting in an unattractive and unlevelled deck finish.

Aluminum, steel, and composite make some of the best subframes for composite decking. Aluminum is lightweight and resistant to rust, while steel is strong and durable.

Composite subframes are made from wood and plastic, offering the best materials. Since they vary in strength and durability, research can help you find the best option for your deck's needs.


Composite decking installation errors can make your investment less secure and impact longevity.

Familiarize yourself with the common composite decking installation mistakes to avoid.

Now that you know this knowledge, take the necessary steps to ensure a successful composite decking installation.

And don't forget to share this article with others who might find it helpful!