5 common deck build mistakes — visualized on one framing

Statistically, missing or improper ledger flashing — it's responsible for the largest share of catastrophic deck collapses on attached decks. Water sits on top of an un-flashed ledger, migrates down behind it, rots the band joist invisibly over 5-10 years, then a party load pulls the lag bolts out of spongy wet wood. Per CPSC and inspector reports, ledger failure causes about 90% of attached-deck collapses.

Most jurisdictions do 3 inspections: (1) pre-pour — checks footing depth + diameter via photo or in-person before concrete arrives; (2) framing — checks ledger flashing layers, hanger nail count + type, joist spans + spacing, blocking, post-to-beam connectors; (3) final — checks railing height + baluster spacing + stair geometry. They're looking specifically for: flashing layers (visible top z-flashing), correct nails in hangers (10d common, not deck screws), blocking at mid-span on long joists, and the right fastener material for treated lumber.

Yes — frequently. The Simpson published load rating assumes EVERY nail in the schedule is installed. A LUS210 rated for ~1,065 lb download requires all 18 nails. Skipping the 8 joist-side nails (the most common omission) cuts the rated capacity by roughly half — to ~530 lb — and removes the joint's ability to resist lateral or uplift forces. With a single hanger that's still fine at static load; with 12 half-nailed hangers across a deck under a 30-person party, the cascade failure scenario is real.

Modern pressure-treated lumber uses copper-based preservatives — MCA (micronized copper azole), CA-C (copper azole), or ACQ (alkaline copper quat). The copper ions are electrochemically active. When standard galvanized steel contacts copper-treated wood with any moisture present, galvanic corrosion eats the zinc coating off the steel within 12-24 months. Solutions: hot-dipped galvanized (HDG) with G185 coating (3× the zinc of standard galv), stainless steel (304 or 316 — required for marine/saltwater), or polymer-coated structural screws rated for ACQ contact.

Blocking is short 2× lumber pieces installed perpendicular between joists at mid-span (and over interior beams). It does two jobs: (1) prevents joists from rolling / twisting under load, especially the outer rim and joists near railings, and (2) transfers lateral load between joists so the deck framing acts as a unified diaphragm instead of independent beams. IRC R507.5.1 requires blocking at mid-span for joist spans ≥ 10 ft. Most DIY builds skip it because it's tedious; pros always include it because every framing inspection looks for it.

Standard deck screws — NO. Their hardened steel shafts are brittle and snap in shear under cyclic load (people walking, rocking chairs). Joist hanger published ratings are based on 10d common nails OR specific approved screws. Simpson SD9 / SD10 Connector screws are explicitly rated as nail substitutes and have a tougher metallurgy that bends under overload instead of snapping. Cost is comparable; use Simpson SD screws or 10d common nails, NOT regular #9/#10 deck screws.

Build to the IRC checklist: (1) full 5-layer ledger flashing — sheathing, WRB, back flashing, ledger + lag, top z-flashing; (2) every nail hole in every hanger filled with 10d common nails or Simpson SD Connector screws; (3) footings extend below local frost line (look up your zone on DeckMath's Footing Calculator); (4) HDG G185 or stainless fasteners in all PT lumber contact; (5) mid-span blocking on any joist run ≥ 10 ft. The other 14 animations in this library cover each step in detail.