“We like to picture frame [our decks] and then bring the post inside the deck a little ways,” Leonard says. “And if we have double rims, like a flush beam situation, we’ll be notching out our posts to the thickness of one of those joists; but if it’s a composite post, you can’t do that. It’s not strong enough. We almost never mount on the exterior of a deck, and we’re always going to double, so we always seem to be running into that problem.”
Solutions tend to differ from project to project, Leonard says, depending on the project and the customer’s budget and taste. Most recently, he says, creating a custom steel rail system for the deck solved the problem.
Manufacturers are looking to address those concerns, Bizarri says, but face the dual challenge of reducing the weight of composites without limiting structural integrity. Recently, TimberTech introduced chemical foaming — a process common in the plastics industry — to its manufacturing process to reduce the weight of its composite boards.
“Essentially, you’re introducing more air into the same space, which lets your product be lighter,” Bizarri says, of the foaming process. “It does affect the structural properties, so the long-term objective is to find properties that are strong enough to meet the needs of the application.”
TimberTech engineers are also working to apply processes used to make the company’s composite fencing products, including foaming and inserting metal rods into extruded boards for horizontal applications. “There are challenges with structural integrity, especially in horizontal components,” Bizarri says, “but adding a metal insert with an extrusion process has worked in our fencing, so that’s a way we’re attacking it.”
A LITTLE GAP GOES A LONG WAY Other contractors have run into trouble with the contraction and expansion that composites undergo as a result of seasonal temperature changes. “Composites will expand in summer and contract in winter,” says Kansas City remodeler Dick DeVuyst, owner of high-end deck specialist Outdoor Environments. “The installation technique must account for that. You have to pay particular attention to the temperature when you install it. It makes a difference in how you gap your end joints and butt joints, and how you miter your trim.”
One deck specialist in the Midwest had so much trouble with extreme movement that he swore off composites entirely and now refuses to work with them. The contractor, who asked not to be named because he is still negotiating warranty settlements with several manufacturers, says he lost $250,000 over a two-year period warranting composite decks. One deck he says, “pushed so much that it flattened the downspout completely up against the house — it moved 2 or 3 inches. “If you’re going to move a product 2 or 3 inches and it’s in wood with nails, you know you’re pulling joists and pulling nails and breaking fasteners. It’s some major stuff.”
Though manufacturers specify gap widths based on installation temperatures, the remodeler says, different boards may be installed at different temperatures. “If you have a stack of synthetic lumber out in the driveway and the top has been heated by the sun but the bottom’s cool from the concrete, and you’re pulling it all down that day, every board you put down has a different temperature. So you can gap it all evenly, but when you put it down it expands or contracts different amounts.”
DeVuyst says that he only installs with one composite brand, Trex, because, after years of installing it, he knows how it will react to temperature changes. “I like to stick to one [product] because I know what it does. The worst thing for a contractor like us is to go out to a job two years later and find everything’s all out of place because we didn’t gap it right.”
Bizarri, acknowledging some of composite’s early troubles, places the product somewhere in the middle of its development. “We’ve made a lot of improvements, and the product will continue to improve,” he says. “Frankly, this category is evolving, and will continue to evolve.”
Leonard, the Des Moines remodeler, for all his dissatisfaction with composites in their current state, says he has faith in the power of the market to force manufacturers to make a better product. “They’re going to have to be competitive in the marketplace, or they’re not going to be there.” —David Zuckerman writes frequently on construction topics from his home in Brooklyn, N.Y.