A deck tells on itself if you know where to look. Soft or springy boards underfoot usually mean moisture has reached the framing. Rust stains bleeding from fasteners, railings that flex when leaned on, and stairs that feel bouncy are all structure questions, not surface questions.
The rule of thumb pros use: the surface is replaceable, the frame decides everything. If joists and posts are sound and the ledger is solidly attached to the house, swapping deck boards and railings is a repair — days of work, a fraction of the price of a rebuild.
If framing is rotted, footings have shifted, or the connections to the house no longer meet code, cosmetic repairs are money poured into a frame that can't be trusted. In those cases a clean demolition and a new build on the same footprint is often cheaper over five years than chasing boards.
Bay Area microclimates matter too. Fog-drenched west-facing decks age differently than sun-baked ones in Millbrae or Belmont, which is why any honest assessment starts with what your deck is actually exposed to — not a generic checklist.
If you're unsure which side of the line your deck falls on, get a structural assessment before agreeing to any quote. At ISMA Builders it's part of every free estimate: we tell you what can stay and what has to go, in writing.