Deck Fastener Code Requirements

Simpson Strong-Tie SDWS

SDWS22 (1/4" x 3" to 6") for ledger-to-rim attachment; SDS (1/4" x 1-1/2" to 6") for hanger installation as substitute for HDG nails. ICC-ESR-2236.

GRK Fasteners RSS

Rugged Structural Screw (5/16" x 4" to 8"). Climatek coating for PT contact. Common alternative to lag screws for ledger attachment. ICC-ESR-2442.

FastenMaster LedgerLOK

Ledger-specific screw (3-5/8" and 5" lengths). Installs without pre-drilling. Published spacing tables equivalent to 1/2" lag at standard IRC patterns. ICC-ESR-1078.

FastenMaster TimberLOK

General framing screw (6" to 10" lengths) for timber-to-timber structural connections. Good for doubled beams, post-to-beam, and heavy framing. ICC-ESR-1078.

Simpson Strong-Drive SDWH

Timber hex head screw for heavy framing (up to 12"). Direct substitute for lag bolts in many structural applications.

Can I use regular screws on pressure-treated lumber?

No. Standard interior screws, drywall screws, and plain steel fasteners corrode rapidly in modern ACQ (alkaline copper quaternary) or copper-azole pressure-treated lumber. The copper in the preservative accelerates zinc and steel corrosion through galvanic action. IRC R317.3 requires fasteners in contact with preservative-treated wood to be hot-dip galvanized (ASTM A153 Class D, minimum G185 coating), stainless steel (Type 304 or 316), silicon bronze, or copper. Regular #8 bugle-head deck screws from the interior aisle will rust out in 2 to 5 years and cause the board to split around the rusted shank.

What is the difference between hot-dip galvanized and electroplated?

Hot-dip galvanized (HDG) fasteners are dipped in molten zinc, producing a thick coating (G185 = 1.85 oz/ft squared of zinc) that metallurgically bonds to the steel. Electroplated or "electro-galvanized" fasteners have a thin zinc layer applied via electrolysis, typically 0.05 to 0.4 oz/ft squared. Electroplated fasteners are NOT approved for ACQ or copper-azole lumber — the thin coating fails in months. Always look for the ASTM A153 marking or the "HDG" stamp on the box. If the package just says "galvanized" without specifying hot-dip or class, assume it is electroplated and do not use it on pressure-treated wood.

Do I need stainless steel at the beach?

Yes. In coastal or saltwater environments (within roughly a half mile of the ocean, or anywhere with regular salt spray), Type 316 stainless steel is the only fastener that holds up long-term. Hot-dip galvanized will still corrode from chloride attack, just slower than electroplated. Type 304 stainless is acceptable for most residential use but Type 316 adds molybdenum for marine-grade chloride resistance. Simpson makes a ZMAX (G185) and a stainless (316) line for every common connector. Expect stainless to cost 3 to 5 times more than HDG — but replacing a corroded deck in 7 years costs more.

Can I use deck screws on the ledger board?

Standard #8 or #10 deck screws are not acceptable for ledger attachment. IRC R507.9.1 requires 1/2-inch lag screws or through-bolts, OR approved structural screws tested under ICC-ES (like Simpson SDWS22, GRK RSS, or FastenMaster LedgerLOK) installed per the manufacturer's published pattern. Ordinary deck screws lack the shear strength, withdrawal capacity, and ductility required. A ledger attached with deck screws will fail catastrophically. See our ledger board code page for full fastener spacing.

How do I identify ACQ-rated hardware?

Look for one of these markings on the packaging or the connector itself: "ZMAX" (Simpson's G185 triple-zinc coating), "HDG" with ASTM A153 Class D reference, "Type 304" or "Type 316 stainless", or a polymer-coating rating (such as FastenMaster TRUSS LOK or GRK Climatek) that specifically lists approval for pressure-treated contact. Simpson, USP, and MiTek all publish compatibility charts. If a connector is silver-colored and shiny without any marking, it is probably electroplated G60 and not acceptable for PT framing. When in doubt, stick with the ZMAX line for galvanized or the SS (stainless) line.

What fastener types work with composite decking?

Composite decking uses three common fastener systems: (1) Hidden clips (Trex Hideaway, TimberTech Concealoc, CAMO Edge) that screw into the joist and grip a groove in the board edge, leaving the top surface unpenetrated; (2) Face-screw with color-matched composite screws (Cortex, StarBorn) driven through the top of the board into the joist with a matching plug filling the head; (3) Plug systems (TigerClaw plug, FastenMaster Cortex) that combine a hidden screw with a filler plug. Never use standard wood deck screws on composite — the heads split the cap-stock and most composite warranties require an approved fastener system.

Do joist hangers need to be pressure-treat rated?

Yes. Any hanger, post base, post cap, or connector that touches pressure-treated lumber must be rated for the chemical contact. Simpson's ZMAX line (G185 triple zinc, 1.85 oz/ft squared coating) is the residential standard for PT contact. For coastal or high-chloride environments, upgrade to Simpson's 316 stainless line. Standard G90 galvanized hangers from the interior framing aisle will corrode through in 3 to 7 years in ACQ and MUST NOT be used on a deck. Check the stamp on the hanger itself — ZMAX parts have "ZMAX" stamped visibly.

What is the torque spec for lag bolts?

IRC does not publish a specific foot-pound torque, but manufacturers and AWC DCA 6 recommend tightening 1/2-inch lag screws until the washer deforms slightly into the wood surface — typically 25 to 40 ft-lbs for a snug, fully seated fit. Do NOT over-torque: crushing the wood fibers reduces capacity rather than increasing it, and stripping the threads destroys the connection. Always pre-drill the pilot hole: 1/2-inch lag = 5/16 inch pilot for the threaded portion, 1/2 inch clearance for the shank. Under-sized pilots split the wood; oversized pilots strip. Use a ratchet with an impact socket, not an impact driver.