Deck problems

Rot and water damage usually start where water sits: at the ledger board against the house, at post bases, and under planters or mats. Corrosion-resistant flashing is required at any ledger board connection to a wood-framed wall, and where flashing was skipped or done badly the ledger rots quietly behind the siding. That is the single most dangerous failure on a deck, because the ledger is what holds the deck to the house.

Sagging means the framing is undersized, over-spanned, or failing. Repair runs $750 to $10,000, and at the top of that range you are comparing against a full replacement at $6,000 to $18,600 for a 300 square foot deck. Get the joist size, spacing, and span measured — allowable spans are prescriptive, and an over-spanned joist will never stop sagging.

Unsafe railings. Guards are required on decks more than 30 inches above grade, with a minimum height of 36 inches, openings that will not pass a 4-inch sphere, guard posts of at least 4x4 nominal, and maximum 6-foot spacing between posts. A guard you can rock by hand has a post attachment problem. Stop using the deck until it is fixed. Railing repair is $25 to $100 per linear foot.

Failed inspections and rejected permits almost always come down to the same short list: footing depth, ledger attachment and flashing, guard post attachment, and stair geometry. None of those are judgment calls; they are measurable. If a builder tells you an inspector is being unreasonable about one of them, get a second opinion.

How to choose

Treat any ledger problem as urgent

The ledger is the connection to your house. Rot, missing flashing, or nails instead of proper fasteners is a stop-using-the-deck situation, not a spring project.

Push-test every guard, every spring

Guards must be at least 36 inches high on decks over 30 inches above grade. Movement at the post base means the attachment is failing.

Price sagging repair against replacement immediately

Sagging repair spans $750 to $10,000 while replacement of a 300 square foot deck is $6,000 to $18,600. Get both numbers before you authorize anything.

Don't paint over rot

Rot repair at $300 to $5,000 is far cheaper than the structural repair it becomes. Probing soft spots with a screwdriver costs nothing.

Termite damage needs two trades

Repair runs $500 to $10,000 and fixing the wood without treating the infestation just buys time.