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Installation & Maintenance

How to Ensure Proper Deck Board Spacing for TimberTech Decking

November 27 2019
joist spacing decking fasteners
Deck Board Spacing for Composites-Featured Image.jpg

Deck board spacing is crucial for the looks and health of a deck – it’s not one size fits all. This article covers why the material type and the fastener used need to be considered.

For centuries, decks have been constructed using traditional lumber with little regard for proper deck board spacing. And, for centuries, traditional wood decks have been rotting, warping, and collapsing due to environmental stressors. In the simplest terms, wood decks are not built in climate-controlled environments and are susceptible to expansion and contraction due to moisture.

Wood fibers swell as they absorb moisture and shrink as they release it, causing the wood to expand and contract.

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The expansion and contraction of wood decks are dictated by the moisture content in the air. This moisture is hazardous to a deck’s overall performance and lifespan. It can lead to rotting, warping, splitting, and cracking.

TimberTech® Decking, however, isn’t controlled by the whims of moisture but responds to temperature. Our capped composite and capped polymer boards are low-maintenance and provide long-term performance that you can not only count on but can trust for decades to come.

Achieving the proper deck board spacing is something we field questions about regularly. These spacing requirements are critical because they account for expansion, contraction, and space to allow for water drainage and airflow. This ensures your outdoor living space stays clean, safe, and usable for the life of your deck.

And, understanding the deck board spacing requirements and the installation best practices for TimberTech Decking is easy when you consult the TimberTech Installation page.

Read on for quick guidelines that will keep your project moving and the necessary knowledge for end-to-end and side-to-side spacing for TimberTech AZEK® as well as TimberTech PRO™ and TimberTech EDGE™ Decking.

Side-to-Side Deck Board Spacing

To put it plainly, side-to-side deck board spacing is easy. It’s typically predetermined by the fasteners used during install. Simply follow the chart below. Proper side-to-side deck board spacing allows for air, water, and debris to flow around the decking, leading to a long-lasting, low-maintenance deck.

Side-to-Side Deck Board Spacing.jpg

  • For TimberTech AZEK® Decking it’s recommended to have a minimum 1/8” to 1/4” side-to-side gap between deck boards.
  • TimberTech PRO™ and TimberTech EDGE™ boards must be a minimum of 1/8” to a maximum of 3/16” deck board spacing.

Pressure-treated lumber is typically installed without a gap since the boards will shrink when they dry, creating the appropriate spacing. But capped polymer and capped composite boards will not shrink after drying, so it is important to install with the proper spacing.

Capped polymer and capped composite deck boards, on the other hand, are installed at a minimum 1/8” gap between boards because they won’t shrink from drying like pressure-treated decking.

Get into the nitty-gritty details of all side-to-side deck board spacing requirements in our official and detailed installation guides for each decking line (AZEK, PRO, EDGE, and specialty decking). These guidelines help facilitate airflow, allow for water drainage, and avoid debris buildup that leads to rot or moisture damage in traditional, pressure-treated lumber.

End-to-End Deck Board Spacing

Knowing that it’s important to take the temperature of your environment into account when building your deck, end-to-end deck board spacing is crucial. Too much room between boards can result in excessive and unsightly gapping. Too little room in-between deck board spacing and your deck boards could buckle when they expand.

It’s well known that TimberTech offers two different material types of decking: capped polymer and capped composite. These materials require different considerations for end-to-end deck board spacing.

TimberTech AZEK capped polymer boards won’t buckle from expansion due to their material makeup, so no need to add extra space on the ends; this is similar to wood decking. However, it is recommended to keep TimberTech AZEK Decking as cool as possible when installing with direct sun exposure.

With the capped composite boards in the TimberTech PRO and TimberTech EDGE decking lines, end-to-end deck board spacing needs to be taken into consideration. This is because proper deck board spacing varies based on temperatures at initial installation. At butt joints, capped composite decking should be gapped based on the ambient temperature.

The chart below clarifies the appropriate deck board spacing based on the temperature at the time of installation.

Butt Joint Gapping Requirements.jpg

For adjoining structures or posts, remember to always allow for a 3/16” minimum gap where the decking meets the structure.

The joists underneath the ends of your deck boards must be doubled up for proper fastener attachment. Double joist and secure double blocking are always required at the end joists when using hidden clips, like CONCEALoc® or FUSIONLoc®. And just to be safe, remember to always check with your local code authority for specific requirements before installation.

Airflow and Water Drainage

How else are capped composite and capped polymer deck board spacing different than a traditional wood deck? We’re glad you asked!

Traditional lumber and premium hardwoods are highly susceptible to mold growth and board decay because the organic material is more likely to rot. Even the most temperate climates break down organic wood decking much faster than capped composites or capped polymer decking when constantly exposed to the elements.

Water drainage and airflow are critical to deck board spacing because mold and moisture damage threaten to ruin your deck’s aesthetics, substructure, and life span – especially with wood decks. Even though there’s significantly less of a chance of that happening with composite decking, it’s best to be vigilant.

Deck Board Spacing Made Easy

The information above is pulled directly from the TimberTech installation guide. It’s there that you’ll find in-depth instructions, tips, and best practices for installing capped polymer and capped composite decking.

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