Composite decks: what to know
What composite decking is
Composite boards are made from wood fiber and plastic, pressed into boards that look like lumber. They don't rot the way wood does, and they never need stain or sealer.
Almost all boards sold today are capped: a hard plastic shell wraps the core on three or four sides. The cap resists stains, fading, and mold far better than the uncapped boards of the 1990s and 2000s, which gave composite a bad name.
Composite vs. PVC boards
PVC boards, sometimes sold as cellular PVC, have no wood fiber at all. They weigh less and hold up better where water sits, such as near pools or in deep shade. They usually cost more than capped composite.
Both come in many colors and grain patterns, and both are built on the same kind of frame.
What drives the cost
Composite boards cost more than pressure-treated lumber, but the boards are only part of the price. Deck size, height off the ground, stairs, railing type, and how hard the yard is to reach often move the total more than the board line you pick.
Over 15 to 20 years, skipping the stain or sealer a wood deck needs every few years closes part of the gap.
What sits under the boards
Composite decks are almost always framed with pressure-treated lumber. The frame holds the deck up, so it matters as much as the boards you see.
- Footings that go below the frost depth your township sets, so the deck doesn't heave in winter.
- A ledger bolted to the house and covered with flashing, so water can't rot the house wall.
- Joists spaced to the board maker's rules: often 16 inches apart for straight boards and 12 inches for diagonal layouts.
- Many builders also cover the tops of joists with butyl tape, which sheds water and slows rot in the frame.
Hidden clips or screws
Most grooved boards use hidden clips that sit between the boards, so the surface has no screw heads. Boards at the edges and on stairs are often screwed through the face with color-matched screws.
Composite grows and shrinks with heat and cold, so boards need the end and side gaps the maker calls for.
Heat, color, and grip
Composite gets hot in full sun, and dark colors get hottest. If the deck faces south or west with no shade, a lighter color or a pergola helps. Boards with a deeper grain give better grip when wet.
Upkeep
- Wash once or twice a year with soap and water or a cleaner made for composite.
- Clear leaves and pollen from the gaps so water drains. Mold grows on dirt left on the surface, most often in shade.
- Use a plastic shovel in winter and an ice melt the board maker approves.
- Scratches in capped boards can't be sanded out like wood, so use pads under grills and heavy furniture.
Railing options
- Composite or PVC: matches composite boards and needs little upkeep. Usually comes in white, black, and wood tones.
- Aluminum: powder-coated, won't rust, and has thin balusters that block less of the view.
- Cable: stainless steel cables for the most open view. The end posts must be strong enough to hold the cables tight, and the cables must stay tight to pass the 4-inch rule below.
- Wood: the lowest cost. Needs the same stain or paint schedule as a wood deck.
Any deck more than 30 inches above the ground needs a guard at least 36 inches tall, with gaps too small for a 4-inch ball to pass through. Railing posts are a common weak point, so they should be through-bolted or set in tested brackets, not held by a few screws.
Stairs, landings, and multi-level decks
Sloped yards and walkout basements often call for a tall deck or two levels joined by steps. Splitting a high deck into levels breaks up the height, can leave room for a covered patio below, and gives separate spaces for cooking and sitting.
Wide stairs with a landing are easier to climb and can double as seating. Code limits how tall each step is and how shallow each tread can be, and the steps in a flight must match within a small margin. Stairs with four or more risers need a handrail you can grip, a flight can rise only about 12 feet before it needs a landing, and the bottom step should sit on a firm base, not bare soil.
Is composite right for you?
Composite often makes sense if:
- You plan to stay in the house for years.
- You don't want to stain or seal every few years.
- Part of the deck sits in shade, where wood stays damp.
