One deck, quotes from $14,000 to $77,000: why bids spread so far and how to compare them

The poster also complained that contractors charge a lot and do poor work. A fivefold spread is wide, but a deck has many places where price can hide. Zonda's 2025 Cost vs. Value report, the industry's yearly benchmark, puts the national average for a 16-by-20-foot wood deck addition at $18,263 and the composite version at $25,096, so the decking choice alone moves that spec by about $6,800.

Height and structure move it further. The American Wood Council's DCA 6 guide, built on the IRC, requires a guard on any deck more than 30 inches above grade, posts of at least 6x6 and footings on undisturbed soil below the frost line, with footing size growing as beam and joist spans grow. A ledger must be flashed and bolted to a band joist that can carry the deck, plus two hold-downs rated at 1,500 pounds; where the house cannot take a ledger, the guide calls for a freestanding beam and more footings. A low number that leaves out the permit, the hardware or the flashing is pricing a different deck.

The Federal Trade Commission tells homeowners to collect several written estimates listing the work, materials, completion date and price, not to take the lowest automatically, and to ask for an explanation when they differ widely. Its guidance also says to hire only licensed and insured contractors, to be wary of anyone who wants the owner to pull the permit or pay everything up front, and to hold the final payment until the job is done.

The practical fix is one drawing and one spec sheet for every bidder: size and height, decking and railing products, footing type and depth, ledger or freestanding, stairs, demolition, permit and inspections. Bids returned on that sheet can be read line by line, and an outlier shows which line it differs on.