Decks fail in one of two ways, and both are preventable
Deck failures are not gradual. They are sudden, they happen when the deck is loaded with people, and they concentrate in two details: the ledger connection where the deck attaches to the house, and the footings underneath it.
The ledger is the one that causes the serious collapses. A deck nailed to a house rather than through-bolted or lag-screwed into structure, or fastened without flashing so water gets behind it and rots the rim joist, is the classic case. It looks perfect for years. Any deck contractor worth hiring will describe the ledger attachment and flashing detail without being prompted, and a homeowner should ask a bidder to explain it before comparing prices.
The second is footings, which is where the local ground comes in.
Footings on Columbia's soil
Columbia sits near the fall line, where the Piedmont meets the coastal plain, and the sandhills soils here are notably sandy compared with the red clay further upstate. Sand drains well, which is good for a deck, but it also means bearing capacity depends on reaching properly compacted material rather than assuming a standard hole depth will do.
Frost depth is shallow in this part of South Carolina, so the northern rule of thumb about digging below the frost line is not the binding constraint here. Bearing is. A footing that is wide enough and deep enough to carry the load without settling matters more than depth for its own sake, and the required size depends on the load the post carries — which depends on the beam span and the joist span above it.
A contractor who quotes footings without reference to what each post is carrying has not sized them. That is worth noticing.
South Carolina licensing and permits
Residential contractors in South Carolina are licensed or registered through the Department of Labor, Licensing and Regulation, with the requirement varying by type and value of work. Ask for the number, verify it on LLR's public lookup, and check what classification it covers.
Decks above a modest height generally require a permit and inspection, and the inspection exists specifically to look at the ledger and the footings — the two things a homeowner cannot evaluate later. A contractor proposing to skip the permit is proposing to skip the only independent check on the parts most likely to hurt someone.
Confirm whether the City of Columbia or Richland or Lexington County issues the permit for the address; they administer separately, and the surrounding municipalities differ again.
Surface temperature is a Columbia-specific decision
This city gets genuinely, famously hot, and it matters for decking selection in a way it does not in a milder climate. Composite and PVC decking absorb and hold heat, and dark colors in full afternoon sun can reach surface temperatures that make a deck unusable barefoot during the hottest part of a summer day — which is a real problem if the deck is there to be used.
Three things reduce it: choosing a lighter color, choosing a product line that is engineered for lower heat gain, and orienting or shading the deck so it is not in unbroken west-facing sun. Anyone selling composite decking in this market should be able to talk about this. If the conversation is purely about color and warranty, ask directly.
Wood runs cooler underfoot but demands maintenance, and pressure-treated southern yellow pine in this humidity will check and cup if it is not kept sealed. Neither material is the obvious answer; they are a genuine trade-off between comfort, upkeep and cost.
Questions that separate bids
- How is the ledger attached, and what is the flashing detail?
- What size are the footings, and what load did you size them for?
- Is a permit being pulled, by whom, and which office issues it?
- What are the joist and beam spans, and what species or product?
- For composite: what is the heat performance of this line and color in full sun?
- What is the hardware — are fasteners and connectors rated for treated lumber?
That last one is easy to overlook. Modern pressure-treated lumber is corrosive to ordinary steel, and hardware that is not rated for it will degrade at the connections where it matters most.
Before authorizing work
Verify licensing and insurance independently, confirm the permitting jurisdiction, and get scope, materials, warranty terms, schedule and payment terms in writing before any money changes hands.