Deck Inspection Procedures and Defect Recognition
What this domain tests
This domain asks you to follow the load path - decking, joists, ledger, posts, footings - and judge each connection as a potential failure point. Expect items on where to probe for decay, acceptable fasteners and placement, guard and stair geometry, and separating cosmetic wear from structural deficiency.
Work the load path
InterNACHI's deck material notes that most collapses trace to a failed ledger-to-house connection, while most injuries come from guardrail failure. Confirm the ledger is preservative-treated and bears against the rim joist or a wall designed to carry it - never through siding alone. Fasteners should be 1/2-inch lag screws or through-bolts with washers, staggered and set back from ledger edges. Flashing above the ledger must shed water; corroded or missing metal is a defect, not a detail.
Footings, posts, bracing
Footings below the frost line or at least 12 inches below grade; posts connected to footings and beams with approved connectors, not bolts alone; no wood buried in soil. Decks more than 6 feet above grade need diagonal bracing. Joist cantilevers past a beam should not exceed one-quarter of the joist span.
Guards and stairs
Guards at least 36 inches high with infill that rejects a 4-inch sphere; posts no more than 6 feet apart and not notched; graspable handrail on stairs with four or more risers, 34–38 inches; risers not over 7-3/4 inches, treads at least 10 inches.
Worked example
A 12-foot ledger is fastened with 1/4-inch lag screws at 30 inches on center, driven through 1-inch foam sheathing. Reasoning: the fastener diameter, the spacing and the sheathing standoff all reduce withdrawal capacity below what a deck ledger needs. Report the condition and recommend evaluation by a structural engineer or qualified deck contractor.
Traps that cost marks
Accepting paint or stain as evidence of sound wood - use the pick test at the ledger, joist ends, post bases and flashing line. Also: calling a defect a "code violation" instead of describing the condition, and forgetting deck receptacles (GFCI-protected, weatherproof cover, decks over 20 square feet).