Humid & Rainy Climates (e.g. Coastal, Southern, or Tropical Regions)
In regions with high humidity, frequent rain, or a tropical climate (think the Southeast US, Pacific Northwest, Gulf Coast, etc.), moisture and mold are the biggest concerns. You’ll want a decking material that resists rot, fungus, and insect infestation. Pressure-treated wood was practically invented for these conditions – the chemicals in PT lumber do an excellent job preventing rot and mold even when the wood is often wet. This makes PT pine a very common choice in places like Florida or the Carolinas. Cedar and redwood are also good in rainy climates because of their natural oils; they don’t absorb water as readily and are less prone to decay. In a truly constantly damp environment (like a shaded deck in a rainforest climate), even cedar or redwood should be sealed to keep them from eventually mildewing.
Composite decking shines in damp climates – it won’t rot or grow mold internally, and it can’t be eaten by termites. You may still get surface mildew in the film of pollen/dirt if you don’t clean, but the boards themselves won’t deteriorate due to moisture. This makes composite a low-stress choice for coastal areas or regions with long rainy seasons. Also, composites (and PVC) won’t corrode from salt air in coastal locations, whereas if you use wood near the ocean, you need to use stainless steel fasteners to avoid corrosion. One thing to watch with humidity is slipperiness – algae can grow on wood or composite if it’s perpetually damp, so keep the deck clean or choose a textured surface.
If your area has a lot of insects (like termites or carpenter ants), pressure-treated, cedar, and tropical hardwoods are all naturally or chemically armored against bugs. Untreated softwoods would be a bad choice in such regions. Ipe and similar hardwoods are actually so dense that insects generally can’t bore into them – another reason they’re great for tropical climates. Do note, however, that in very humid climates, wood movement (swelling/shrinking) can be more pronounced. Tropical hardwoods move less because of their density, whereas softer woods might expand quite a bit during the wet season. Proper spacing and ventilation under the deck are critical to avoid cupping boards in these areas.
In summary, for humid and rainy climates, rot-resistant materials are a must. Pressure-treated wood offers a budget-friendly solution that’s specifically made to resist rot and bugs. Cedar and redwood give a more natural, upscale wood option that also hold up well when maintained. For ultimate no-rot assurance and minimal upkeep, composites are extremely popular in these environments (many find the extra cost worth the confidence in longevity). Just remember even “resistant” wood isn’t “waterproof” – you should design the deck with good drainage, gap between boards, and maybe avoid wood-to-ground contact in very wet areas to extend its life.
