Building a deck in a hot and humid climate is a battle against the elements. Between blistering sun UV rays and relentless moisture that leads to mold and rot, the choice of decking material can determine whether your deck lasts 5 or 20 years.
If you live in a coastal area or anywhere else with 90% humidity, 100% Cellular PVC is the gold standard for longevity. It differs from composite decking in that it contains zero wood fibers. Since there is no organic material, it is physically impossible for it to rot or grow mold internally. However, it can get very hot (too hot to walk on bare foot). Luckily, there are now some high-end PVC brands that use heat-reflective technology to keep the boards significantly cooler under foot than traditional composites. Azek (TimberTech) is one of the industry’s leaders for PVC decking that uses “Cool Touch” technology.
Another more budget-friendly option is kiln dried pressure treated wood (also known as KDAT). This is a good option if you refuse to give up the look of real wood but hate the way pressure-treated pine warps in the heat. The boards are “baked” in a kiln at high temperatures, which removes the sugars and moisture that bugs and fungi feed on. Another benefit of KDAT pressure treated wood is that it requires no wait time before staining and sealing. In fact, sealing the wood should be done as soon as possible. The kiln dried pressure treated is much more dimensionally stable than traditional pressure treated boards, which means it won’t expand and contract as much when the humidity spikes. The biggest downside is that it does require some maintenance of applying and maintaining a UV-protectant oil.
Capped composite boards are another option and a good balance of high rot resistance and low maintenance, though they are generally hotter under foot than real wood. One exception to this would be Trex’s “SunComfortable” technology used in their Transend Lineage line of decking, which reduces heat buildup by up to 35 degrees Fahrenheit when compared to their original composite boards. Capped composite boards are “capped” on three or four sides with a polymer shell. This shell acts as a sort of raincoat for the wood/plastic core. Four side capping is more expensive, but a necessity in humid climates. Otherwise, humidity will seep into the core from underneath, leading to “mushrooming” or swelling. Capped composites are highly resistant to fading and staining.
There is yet another newer category of decking that replaces wood fibers with minerals (like ground-up stone), called mineral-based composite or MBC. Because of the materials used for construction, these boards have virtually no thermal expansion or contraction. They won’t budge regardless of temperature or moisture level. Another benefit of these boards is that they often have the best slip-resistance ratings, which may be vital if your deck is in an area with frequent rain.
Whichever option you choose to go with, the secret to longevity in humid climates is airflow. You’ll want to ensure your deck has at least 12-18” of open space beneath the deck. Avoid “skirting” the deck all the way to the ground with solid material. If the air can’t circulate, it will trap moisture underneath, creating a breeding ground for mold, regardless of the quality of boards you choose.