The Short Answer
The common exemption is narrow: a deck that's low (typically under 30" above grade), detached from the dwelling, and not serving a required exit may skip the permit in many California cities — but the exact threshold varies by jurisdiction, so check yours. Everything else — attached decks, tall decks, balconies, roof decks — is permitted work. And a meaningful subset needs an engineer, not just the prescriptive tables.
Prescriptive vs. Engineered
Many jurisdictions publish standard deck details, and simple rectangular decks on flat lots can often be permitted straight from them. Engineering enters when the deck leaves the tables:
| Condition | Why it needs engineering |
|---|---|
| Tall decks / walk-out heights | Post buckling, bracing, and lateral loads grow fast with height |
| Sloped or hillside sites | Footings become site-specific; sometimes piers |
| Ledger can't attach conventionally | Cantilevered floors, brick veneer, or rim conditions outside the tables — a classic collapse point |
| Cantilevers & long spans | Beyond prescriptive span limits |
| Roof decks & balconies | Waterproofing-critical framing, occupancy loads, guardrail anchorage |
| Hot tubs / heavy loads | Concentrated loads the tables never contemplated |
Guardrails Are Structural
Code requires guardrails to resist a concentrated load at the top rail — and that load has to travel through the post, its connection, and into the framing. Notched 4x4 posts bolted to a single rim joist routinely fail this check. On engineered decks the guardrail connection is a designed detail; on inspections, it's an increasingly common failure item.
Balconies and SB 721
California's balcony inspection law (SB 721, and SB 326 for condos) requires periodic inspection of elevated exterior elements on multifamily buildings — a direct legislative response to fatal balcony collapses. For contractors this means two things: balcony repair work is engineering-involved almost by default, and there's steady demand for evaluation letters and repair designs on older buildings.
Built Without a Permit? The Realistic Fix
- As-built evaluation — an engineer reviews the existing structure (photos, measurements, sometimes selective exposure of connections).
- Correction design — usually the ledger, footings, or guardrails need upgrades; full rebuilds are rare.
- Letter or plans to the city — many jurisdictions accept an engineer's evaluation letter plus corrected details for legalization.
- Permit & inspection — done, disclosed, and defensible at resale.
The cost of doing this proactively is small. The cost of doing it after a tenant's guest leans on a bad rail is not a number anyone wants to discuss.