Composite vs wood decking in a South Dakota climate

Wood is a sponge with a grain direction. It takes on water in spring, sheds it in summer, and trapped moisture expands inside the board every time it freezes. Run that cycle through enough winters and you get the familiar results: surface checking, cupped boards, raised grain, fasteners that work loose. Sun does its own work on top of that, breaking down the surface fibers and graying the board wherever the finish has worn thin. Pressure-treated pine and cedar both do this. Cedar is more stable and easier on bare feet, but the same cycle still applies to it.

Capped composite behaves differently because it isn't porous the same way. The core is wood flour bound in plastic, and the cap is a polymer shell wrapped around it. Water sits on top instead of soaking in, so the freeze-thaw cycle that splits wood has less to work with. What composite does instead is move with temperature. It expands and contracts along its length more than lumber does, and this climate swings hard between deep winter and midsummer, which is why end gaps and fastening details aren't optional here. Composite is not refinished the way stained wood is, so the color you buy is the color the cap has to hold. How a specific board holds its color is a question for that manufacturer's published warranty rather than for us.

With wood, the real job is refinishing. Clean it, let it dry, and put stain or sealer back on the walking surface on the cadence the finish manufacturer calls for. Sooner on the south and west exposures, sooner on stairs and rails that take the most traffic and weather. The catch in South Dakota isn't the work, it's the window. You need dry boards and temperatures inside the range the finish requires, and the stretch between snowmelt and the first hard freeze is short. Plan the refinishing around that window rather than waiting until the deck looks rough and then scrambling for a dry stretch.

Composite trades refinishing for washing. Soap, water, a soft-bristle brush, and attention to spills, because grease, leaf tannin, and rust from a planter can all set in if they sit. Follow the manufacturer's limits on pressure washing, since a too-aggressive tip can scar the cap and there's no sanding that out. Composite can't be refinished, so the color you buy is the color you own. In winter, use a plastic shovel with no metal edge, and only the ice melt the maker approves. It's less work than staining, though it still belongs on the list.

Here's the part that doesn't change with the material: everything under the boards. Footings set deep enough that frost can't lift them, at the depth adopted local code requires and the inspector confirms on site. Beams and joists sized for real snow load and for the spans you're actually building. A ledger flashed so water can't sit against the house, because rot behind a ledger is covered by the finished surface. Hardware and fasteners rated for contact with treated lumber, since the wrong metal corrodes inside the connection where nobody is looking.

Those footings are poured concrete, and they're where a deck either gets built for this climate or doesn't. None of it shows in the finished photos. A wood deck on a well-built frame will outlast a composite deck on a failing one, which is why the structure gets looked at first. So if you're re-decking rather than starting fresh, answer this before any material gets picked out: are the footings, posts, ledger, and joists sound enough to carry a deck through another full life? If the frame has gone soft or the footings have moved, that part gets addressed before a new surface goes down.

This is the practical difference that shows up when re-decking an older structure. Composite boards are more flexible than sawn lumber, so they need more support underneath to feel solid underfoot. Every manufacturer publishes a span table for its boards, and that table is not a suggestion. What enforces it is adopted local code plus the warranty terms the manufacturer writes, and building outside it can cost you both. The spacing your deck needs comes off the published table for the board actually purchased, read against local code and confirmed at inspection. Running boards on a diagonal tightens the spacing. Stair treads are usually tighter still. We build to the table for the specific board, not to a rule of thumb.

Older decks were often framed to a wider joist spacing because sawn wood decking could carry it. Put composite on that frame and it can feel springy between the joists, and it will telegraph every crown and dip in the existing lumber. Fixing it means adding joists or sistering the ones that are there, which is real framing work and belongs in the conversation early, before any material gets ordered. There's blocking to plan for too, under picture-frame borders, at butt joints, and anywhere the pattern changes direction.

Composite usually goes down with hidden clips that ride in a groove milled into the board edge. It looks clean and it sets a consistent gap on its own. Where you have to face-fasten, on stairs, borders, and the first and last board, you use the manufacturer's screws and color-matched plugs. Wood gets face-screwed with fasteners rated for treated lumber, stainless or a coating built for that contact, set so the head sits flush without crushing the fiber around it.

Gaps carry more weight than the finished look suggests. Wood shrinks after installation, so boards go down snug and open up as they dry. Composite moves with temperature, so end gaps get sized to the conditions on the day it's installed, which is why a cold morning and a hot afternoon call for different numbers out of the manufacturer's installation instructions. Underneath, both materials want air. A deck sitting close to grade with no ventilation and bare dirt below holds moisture against the framing, and that shortens the frame's life no matter what's on top of it. Keep the surface gaps clear of leaves and needles so water drains through instead of sitting.

We don't hand out a firm answer on material without seeing the yard, the exposure, and the structure that's already there. What we can give you is the set of questions that usually settles it.

How long do you plan to be in the house? How much upkeep do you honestly do, not intend to do? How much direct sun does the deck get, and will people be on it barefoot in July, since darker composite runs hot? Do you want the option to change the color later, which is a wood-only feature? Is the frame getting replaced anyway, which takes the joist-spacing question off the table? And are you matching a railing or stair system that comes from the same product line?

Both answers are legitimate. Wood is not a compromise and composite is not maintenance-free. We install what you choose. On the composite and PVC side, Hols & Co is a TimberTech PRO contractor: TimberTech is the line we work in, and a TimberTech deck we build carries TimberTech's labor warranty on top of the product warranty. If you have your heart set on a different board, say so and we'll price it. Jace walks the site, talks through both, and puts the scope in a written estimate. Call or text (605) 679-5223.