5 Deck Building Mistakes I Made (So You Don't Have To)

It depends on your local building code, but most jurisdictions require permits for any deck where the walking surface is more than 30 inches above grade. Even ground-level decks may need permits if they are attached to the house, exceed a certain square footage (often 200 sq ft), or include stairs and railings. Check with your local building department before starting — penalties for unpermitted decks can include fines, stop-work orders, and requirements to tear down non-compliant work. Some municipalities also require permits for any structure, regardless of height, if it's attached to the primary dwelling.

Wood decking (5/4" or 2×6) is typically installed over joists spaced 16 inches on center, though 24 inches is acceptable for 2×6 running perpendicular to joists. Composite and PVC decking almost always requires 12-16 inches on center — most manufacturers specify 16" OC for perpendicular installation and 12" OC for diagonal installation. Installing composite decking over joists spaced wider than 16 inches voids the manufacturer's warranty and causes visible sagging between joists. Always check the specific product's installation guide — requirements vary between brands and product lines.

Footings must extend below the frost line — the maximum depth at which ground freezes in winter. In the US, frost line depths range from 0 inches in southern Florida to over 72 inches in northern Minnesota. Typical depths: 12" in the Deep South, 18-24" in the Mid-Atlantic, 30-36" in the Midwest, 42-48" in New England. Check your local code for the exact requirement. Footings should be at least 12 inches in diameter for a typical residential deck and should use sonotube forms with a concrete footing at the bottom and a post anchor bracket on top. Never set wood posts directly into concrete or soil.

Use only hot-dipped galvanized or stainless steel fasteners rated for ACQ (Alkaline Copper Quaternary) pressure-treated lumber. The copper compounds in modern pressure-treated wood are highly corrosive to standard steel — common electroplated or interior screws will rust and fail within one to two years. Stainless steel (grade 304 or 316 for coastal areas) is the best choice for longevity. For structural connections (joist hangers, post bases, hurricane ties), use manufacturer-specified connectors with the matching rated fasteners — substituting regular nails or screws in structural connectors is a code violation.

Wait until the wood is dry enough to absorb the sealer — typically 2 to 6 months depending on climate and sun exposure. Test by sprinkling water on the surface: if the water beads up, the wood is still too wet. If the water absorbs into the wood within a few minutes, it's ready to seal. In hot, dry climates, lumber may be ready in 2-4 weeks. In humid or shaded conditions, it may take 3-6 months. Sealing too early traps moisture inside the wood, leading to premature rot and peeling finish. Once the wood passes the water absorption test, apply a high-quality water-repellent sealer or penetrating oil-based stain.