Just six months ago, my friend attained his dream of owning his own home in a little country town. It’s a good place for him, his daughter, and his girlfriend, and it came with bonuses like a bunch of barn cats and a ground-level back deck to pet them on. He’s working on finding the pony-sized dog his daughter wants.
One morning, my friend went out to feed the cats, and went right through the deck. This prompted some mirth amongst those who know him since he is not a small man. However, when I visited him that weekend it was plain that his weight wasn’t the reason he was left wondering whether to repair or replace his deck. The deck’s substructure was solid, and with joists 16 inches off center, it shouldn’t have had a problem supporting even his ample personage. The issue was that the hollow PVC deck boards had become brittle enough that his weight was enough to break them. Purely PVC deck boards are a new development in decking, and obviously there are some issues to be worked out. Composite decking is also a relatively new product, though. So when it comes to composite decking vs. PVC, which decking lasts longer, and which is really maintenance free?
The Differences Between Composite and PVC Decking
There is a lot of confusion about PVC decking and composites, with one being frequently mistaken for the other. They both contain synthetic materials, specifically plastics. But that is where the similarities end. PVC decking is composed of a single material: polyvinyl chloride (which is probably more familiarly known as the vinyl in vinyl siding and fences). Composite decking is usually created of one or two different types of plastics–either polypropylene or polyethylene–along with wood or bamboo flour. These different compositions change the performance profile of each product.
Known Problems with PVC
Plastics have some known issues that are mitigated when they’re mixed with wood flour. PVC decking has no mitigating additives—at least above the molecular level—and that means that plastic’s issues come out in full force. Some of these are:
- Linear expansion is a problem for all plastics. Because they’re long chain molecules, when they’re warmed, these long molecules stretch out. This is something that engineers take into account in their calculations using the linear expansion coefficient. With an expansion ratio of 54-110 compared to pine’s 5 or steel’s 11, plastic products can change size pretty drastically. PVC deck boards have been known to expand so much that after a hot day the edge of the deck is no longer even.
- Heat retention is a common problem with PVC decks. Under the hot summer sun they can grow uncomfortably hot to walk on with bare feet. This is an impediment to enjoying a summer cookout or even just making it into the backyard in bare feet, and is something my friend had previously complained about with his PVC deck.
- Cold weather brittleness is an issue at the opposite end of the temperature spectrum. In cold weather, plastic has been known to become brittle and crack easily. This may not be a concern with other PVC products like fencing, but a deck is subject to constant impacts from people’s feet. Since PVC’s ductile to brittle transition point (the point at which its physical properties change and it weakens) starts at around 32 degrees F, this brittleness is a concern for people in most states, and it means that PVC is definitely not the best decking for cold climates.
The large expansions and contractions of PVC with changing temperatures can put wear on and even damage the boards and fasteners. UV light also causes the plastic to decay, causing a whitish powder to form on PVC surfaces. All of these factors can make your deck less enjoyable, and over time, less safe. Still, plunging straight through it like my friend did is an uncommon problem.
Composite Decking Vs. PVC: How the Boards Perform on a Deck
Composite boards, on the other hand, either don’t suffer from or have mitigated many of these issues. Instead of PVC plastic, most composite boards use polyethylene or polypropylene, both of which are more dimensionally stable than PVC, with expansion coefficients of 59.4 and 72-90 respectively. Reinforcement lowers it further, with fiberglass-reinforced polypropylene having a linear expansion coefficient of only 32. The expansion of composite varies, but when the ratio of wood flour to plastic rises above 40%, composite deck boards become much more dimensionally stable and far more rigid.
This rigidity is a major advantage of composite decking compared to PVC. A long-term issue with plastic decking is that it creates a bouncy deck. This means that there is enough flex in the deck boards that the deck’s surface depresses with every footfall and springs up when the foot is lifted. This was an issue with first generation composite decking, remains an issue with current low-quality composite decks, and is pronounced with PVC decks. The solution is usually to move the deck joists closer to each other. This is less than ideal because it requires using more materials to build the substructure and raises the costs of building the deck.
PVC does have an advantage over composite in moisture resistance and rot resistance. Since PVC deck boards are plastic all the way through, even if the surface of the board is damaged and allows moisture to intrude there is nothing there to absorb the water or to cause rot. However, PVC is still subject to the same potential for damage from trapped water freezing as composite or wooden deck boards are. And if PVC decking begins cracking due to sun exposure, this can provide a path for water to begin damaging the structure of the boards.
Composite Is a Clear Winner
Many of the problems reported with PVC decks are very similar to what was reported early on with composites. Over time, manufacturers of composite decking were able to work out many of these issues, resulting in more reliable decking. In some cases, manufacturers were inspired to go into the industry to create a better product by these early failures. The result is high-quality, fully-capped composite deck boards that better resist moisture and fading from sunlight.
It may be that PVC manufacturers will eventually be able to address the flaws of their products. An early step in this direction is cellular PVC, which is a sort of PVC foam that has a better performance profile than the hollow PVC boards that were used previously. However, these higher-end PVC boards are more expensive than most composite boards, have a plastic look that has gotten complaints, and can delaminate. While PVC board manufacturers may work out the kinks of wholly synthetic deck boards one day, my friend needs a replacement deck now, and I plan to recommend high-quality composites to him.
There are lots of composite decking brands available, but Infinity composite decking by Fortress Deck is unique. It’s a bamboo-based composite decking with a rigidity that compares favorably to wood–requiring no extra joists–and it’s fully capped, making it durable and resistant to sun and moisture. An unparalleled defense against the elements is one of the distinguishing features of Fortress’ products, and can be found in Fortress Fence and Fortress Railing’s lines of wrought iron-look fences and railings that stand up to any weather.