Composite vs. Pressure-Treated Decking in Columbia, SC

This is the first real decision on almost every Midlands deck, and it is not close to a tie. Pressure-treated wood costs less to build and more to own. Composite costs more to build and almost nothing to own. Nearly everything else follows from that.

The short answer

If you plan to be in the house long enough to stain a wood deck three or four times, composite usually wins on total cost. If you are building to sell in the next few years, or the budget is the constraint, pressure-treated is the honest pick and there is nothing wrong with it.

You are choosing a surface, not a deck

Worth clearing up first, because it changes how the price difference feels: both decks are built on pressure-treated wood. Composite decking is not structural. It cannot carry a load across a span, so the posts, beams, and joists under a composite deck are the same treated southern yellow pine that a wood deck is built from.

What you are picking is the walking surface, the railing, and the trim. That is why the two decks are much closer in price than the per-board numbers suggest, and it is why a composite deck does not last forever on its own terms. The frame under it still ages the way wood ages, which is a good argument for getting the framing details right whatever you put on top.

One spec consequence people get caught by: composite is more flexible than wood, so most manufacturers require tighter joist spacing than a wood deck needs, and tighter still if boards run diagonally. If you are converting an old wood deck to composite, the existing frame may not be spaced for it.

Composite runs hotter in the sun. All of it does

This is the complaint we hear most from people who already own a composite deck, and it is the thing the sales literature is quietest about. It is not a bad-brand problem or a dark-board problem: composite in general runs warmer in full sun than wood does.

The reason is physical. Composite board is dense and solid, so it takes on the sun's heat and holds it. Wood is a poor conductor and full of air, so it stays nearer air temperature and sheds heat faster. On a July afternoon in Columbia, on a west-facing deck with no cover, a composite deck is noticeably warm to stand on. Every major manufacturer publishes guidance on it, which tells you it is real.

Two things soften it, and both are decided before you buy:

• Cover and shade. A screened porch, a pergola with real coverage, or an afternoon shade tree takes it off the table almost entirely.
• Color and line. A light board does run cooler than a charcoal one, and some manufacturers now market specific lines on surface temperature. Neither makes composite cool — they make a warm deck less warm. Ask for the manufacturer's own numbers rather than a showroom opinion.

It also has a clock on it. Composite gives the heat up quickly once the sun moves off, so an evening deck is a non-issue. It is the mid-afternoon that you notice.

Railing is where the budget actually splits

People compare deck boards and then get surprised by the quote, because railing is a large share of the cost on a small deck and it rarely follows the same material as the floor.

On a wood deck, the default is a wood railing, and here is the honest part: the railing is the highest-maintenance thing you will own. The deck floor is a flat surface you can pressure-wash and roll a coat onto in an afternoon. A railing is posts, top and bottom rails, and a baluster every few inches, all of which have to be brushed by hand and all of which weather from every side. Most wood decks we see that have been let go were let go at the railing first.

On a composite deck, the railing is usually aluminum or a composite system rather than wood, because there is no sense in bolting an annual chore onto a surface you bought to stop maintaining. That is the right call, and it is also the line item that moves the number. Aluminum railing with black balusters is the common Midlands choice and it does two useful things: it never needs a finish, and it disappears visually, so a deck that looks at trees keeps looking at trees.

If a wood deck is the pick and you want to spend money in one smart place, spend it here: a metal railing on a pressure-treated deck is a legitimate combination, and it removes most of the future work.

How each one behaves in the Midlands

South Carolina is hard on a deck: humidity, hard afternoon sun, and storms that soak it and then bake it dry.

Capped composite does not absorb water, so it does not rot, cup, or splinter, and the shell holds its color instead of bleaching out. Two honest caveats. It is low-maintenance, not maintenance-free: a shaded, north-facing composite deck under trees will still grow mold and algae on the surface and needs washing, because the mold is living on pollen and dirt sitting on the board, not on the board itself. And the cap is a shell, so deep scratches and grease from a grill are permanent in a way they are not on wood.

Pressure-treated pine handles the climate fine as long as it gets its finish on schedule. Left alone, it silvers out in about two years and starts checking, and eventually a board needs replacing. Two things worth knowing going in:

• New treated lumber has to dry before it takes a finish. It arrives wet with treatment. Seal it too early and the coat will not bond. Plan on waiting, then staining, and do not let the wait become never.
• Wet PT boards go down tight, butted edge to edge, because they shrink as they dry. The gaps open on their own over the first few months. A wood deck installed with gaps already in it ends up with gaps you can drop a phone through.

When each one wins

Choose composite when

• You want to stop maintaining a deck surface, permanently.
• You are staying in the house long term.
• You want it to look the same in year ten as year one.
• Splinters are a real consideration for how the deck gets used.

Choose pressure-treated when

• The budget is the deciding constraint.
• You are selling within a few years.
• You want the option to change the color later, which composite does not give you.
• You would rather have real wood and you will actually finish it. Worth knowing this one cuts both ways: composite comes in wood-grain finishes now, and a good one is convincing, so "I want it to look like wood" is not by itself an argument for pine.

Full numbers for both are in the composite deck cost guide and the pressure-treated deck cost guide. If you are sizing a deck before pricing it, how to measure a deck covers that first.