Ask three contractors for a deck price and you'll get three numbers that don't agree — because the price of a deck is driven less by its size than by what's under and around it. Slope, access, soil, height off the ground, and the railing you choose all move the number more than an extra fifty square feet does.
The big three cost drivers are structure, materials, and access. Structure: a ground-level platform needs simple footings, while a second-story deck on a Sunset District slope needs engineered posts, hardware, and often a permit set. Materials: pressure-treated framing is standard, but the deck surface ranges from redwood and cedar to composites that cost two to three times more and last twice as long. Access: a deck we can stage materials into easily costs less than one where every board comes down a side yard.
In practice, a modest ground-level deck on the Peninsula starts in the low five figures, and multi-level or hillside builds run well past that. The honest way to find out where yours lands is an itemized estimate that shows footings, framing, surface, and railings as separate lines — so you can see exactly what each upgrade buys.
One local note: most cities in San Francisco and San Mateo County require a permit once a deck is more than thirty inches off the ground or attached to the structure. We file those permits as part of the job, and a permitted deck protects your home's value when you sell. Right now ISMA Builders is also offering 5% off projects over $1,000 — mention it when you request your free estimate.