Deck solidly.

The part of your deck you never see costs more than the part you do

When my neighbor built his deck in 2023, he picked composite boards, agonized over the color for two weeks, and asked the contractor to match it with a complementary railing. The decking boards came to $3,800. Then the full invoice arrived: $11,200. The other $7,400 went to things he never thought about. Joists. Beams. Post brackets. Concrete for 8 footings. Joist hangers. A ledger board with flashing. A staircase. Two days of labor. The walking surface he spent all his time choosing was barely a third of the bill.

How much a deck costs by size and material

The price ranges below are wide for a reason. Deck costs depend on three things most online estimates ignore. First, height: a ground-level deck needs short posts and no stairs, while a second-story deck needs 10-foot posts and a full staircase. Second, railing: cable rail costs three times what wood balusters cost for the same linear footage. Third, geography: labor in the Northeast runs 40 to 60 percent more than in the Southeast.

Joist spacing: the decision you cannot change later

Joist spacing is set during framing, before a single decking board goes down. Get it wrong and the only fix is tearing up the entire surface, adding or moving joists, and re-laying everything. This is the most expensive mistake in deck building because it turns a $200 framing decision into a $2,000 rework.

Fasteners: why the wrong screw ruins a $10,000 deck

Fastener callbacks account for roughly 80 percent of deck warranty claims and service calls, according to NADRA (North American Deck and Railing Association) member surveys. The problem is almost always the same: someone used regular galvanized screws on a pressure-treated deck. The copper preservative in modern PT lumber (ACQ or CA-B) corrodes standard galvanized coating within 18 to 24 months. The screw heads turn black, stain the wood, and eventually lose holding power. Stainless steel screws or screws specifically rated for ACQ-treated lumber solve this completely. They cost twice as much per box and save the entire deck.

Deck size: what the numbers do to the budget

Deck cost scales with area, but not smoothly. Crossing certain thresholds adds whole categories of expense rather than a proportional amount. A deck under 30 inches above grade needs no guards; cross that line and you are buying railing for the entire perimeter, which on a 16 by 20 deck is 72 linear feet of railing at $25 to $60 per foot installed. That single inch of height can add $2,000.

Beam spans set the next threshold. Widen a deck past roughly 12 feet and the joists need an intermediate beam and another row of footings, so the frame cost jumps rather than creeps. Going deeper is more expensive per square foot than going wider along the house, which is why long shallow decks price better than square ones of the same area.

Permits and inspections

Permits run $100 to $500 depending on your municipality. The inspection checks four things that fail catastrophically when done wrong: the ledger board connection to the house (the leading cause of deck collapses), footing depth below frost line, joist hanger installation, and railing post connections. An unpermitted deck creates insurance gaps and complicates home sales. The inspector is not the enemy. The inspector is the person who confirms your deck will not collapse with 20 people on it during a July cookout.

Footings: what holds the whole thing up

Every deck post sits on a concrete footing that extends below the frost line. That means 36 to 48 inches deep in northern climates, 12 to 18 inches in the South. Each footing is a hole about 12 inches in diameter filled with concrete, roughly 0.6 cubic feet per footing or 2 bags of 80-lb mix.

A typical 16 × 20 deck needs 6 to 9 footings depending on beam spacing and load. At 2 bags per footing, that is 12 to 18 bags of concrete, roughly $90 to $135 in materials. The labor is the expensive part, not the concrete itself. Use the concrete calculator for exact footing volumes and the stair calculator for code-compliant stairs from deck to ground.

One thing contractors sometimes skip on lower decks: they set posts directly on poured concrete pads instead of using post base brackets. This puts the wood in direct contact with a surface that wicks moisture. Within 5 to 8 years the post base rots from the inside out. A $4 galvanized post base bracket on every footing keeps wood above the concrete and adds decades to post life. If your contractor's quote does not include post brackets, ask why.

The ledger is the connection that kills people

More than half of reported deck collapses trace to the ledger, the board that fastens the deck frame to the house. It is the single most load-critical connection on the structure and the one most often built wrong, because nails are fast and lag screws are slow and both look identical once the decking goes on.

Nails are not acceptable. IRC R507.9 and AWC DCA 6 both call for through-bolts or approved structural screws in a specified staggered pattern, sized and spaced to the joist span. Behind the ledger, flashing has to divert water out and over the siding, because a ledger that stays wet rots the house rim joist as well as itself, and by the time anyone notices, the failure is structural on both sides of the wall.

Two things to check on any existing deck this weekend. Look under the ledger for bolt heads or screw heads in a staggered pattern rather than nail heads. Then look for flashing above it, a bent metal or membrane strip tucked under the siding. If you find nails, or no flashing, that is not a maintenance item to schedule; it is the reason to stop using the deck until it is corrected. Freestanding decks avoid the whole problem by carrying their own posts on the house side, which is why some builders skip the ledger entirely on new work.

Where deck projects go wrong

Framing before choosing the decking. Joist spacing is set by the surface material, not the other way around, and most composite brands require 16 inches on center for straight lay and 12 inches for a 45 degree pattern. Frame at 24 inches, then fall in love with composite, and the fix is adding joists to a completed frame. Choose the board first, read its spec sheet, then frame.

Ordering by area instead of by board length. A 16 foot deck built from 12 foot boards has a seam in every run and buys roughly 15 percent more material in offcuts than the same deck built from 16 foot stock. Board length drives waste more than the waste percentage does, and the fix costs nothing at the ordering stage. The waste factor reference covers when to move off the default 10 percent.

Forgetting that stairs are their own project. A deck quote often stops at the deck. Stairs need their own stringers, their own landing pad, their own railing, and they carry their own code requirements under IRC R311.7, which is a separate calculation from anything above. Price them with the deck stair calculator, which returns a printable stringer cut sheet and flags any dimension that fails code.

Skipping the permit. Attached decks and anything over 30 inches above grade need one nearly everywhere, and the inspection exists to catch precisely the ledger, footing, and connection failures listed above. Unpermitted deck work surfaces at sale, and an unpermitted deck that later fails is an insurance conversation nobody wants to have.