InterNACHI Deck Inspector common mistakes
InterNACHI Deck Inspector · Understand the traps and how to avoid them.
Treating the deck as an isolated structure and reporting it without describing how it attaches to the house - missing the ledger board, its fasteners, and the flashing detail entirely.
Candidates study joists, balusters, and stairs as a checklist of parts and mentally file the ledger under 'framing' rather than as the single most consequential connection on the deck. Because the ledger is often partially hidden by siding or a rim joist, it is easy to skip when it is not visually prominent.
What to do instead
Adopt a fixed walk order for every deck: start at the house wall, then move outward (ledger, flashing, joists, beams, posts, decking, guards, stairs). For each component, state condition and the method used to observe it. If the ledger is concealed, report that it was not visible and recommend evaluation by a qualified contractor rather than omitting the item.
Failing to distinguish between a guard post that is merely bolted through the decking or rim with lag screws versus one that is anchored so the guard can resist a lateral load, and reporting the bolted post as acceptable.
A post that feels solid when pushed by hand can still be inadequately connected; candidates rely on the 'shake test' alone and do not look at what the post is fastened to or whether blocking or a bracket transfers load into the joists.
What to do instead
Describe the post-to-frame connection explicitly: what the post bears on, what fasteners or hardware are present, and whether the connection appears designed to resist a load applied to the top of the guard. When the connection cannot be confirmed, report it as a defect requiring correction by a qualified contractor rather than certifying it as adequate.
Measuring baluster spacing at one location and reporting the guard as compliant, without checking the gap along the full run, at the stair rail, and at the triangular opening between the stair rail and the treads.
Candidates treat the guard as a single measurement rather than a continuous condition, and the stair triangle is the least intuitive opening to evaluate and the easiest to forget.
What to do instead
Walk the entire guard line and check the gap at multiple points, including where sections meet, at corners, and along the stair rail. Evaluate the opening formed by the stair tread, riser, and bottom rail as its own condition. Report each location where the gap exceeds the applicable limit and note that a sphere of that size can pass through.
Reporting a deck as structurally sound because the visible framing looks intact, while ignoring rot at post bases, joist ends, and where wood contacts soil or masonry.
Decay is often internal or hidden behind a paint film, and candidates probe only where damage is obvious. Post bases buried in soil or sitting directly on concrete are the classic concealed location.
What to do instead
Use a probe (screwdriver or awl) at post bases, joist bearing points, ledger attachment zones, and any wood near grade. Note in the report where probing was performed and where conditions prevented it. Describe any softened or hollow-sounding wood as a defect and recommend further evaluation, since surface appearance does not establish soundness.
Failing to evaluate the stair stringer, tread, and handrail assembly as a system - checking rise and run but not stringer bearing, tread attachment, or handrail graspability and continuity.
Stairs feel like a separate topic from the deck, so candidates rush them. The handrail profile and the continuity of the graspable rail are subtle requirements that are easy to overlook when the stair 'looks fine.'
What to do instead
Treat the stair as its own inspection sequence: stringer condition and bearing at top and bottom, tread and riser attachment, guard and handrail presence on open sides, graspable profile, continuity, and termination. Report each finding separately so the client understands which element failed.
Writing report comments that state a conclusion without the observation that supports it - for example, 'guard is unsafe' with no location, measurement, or description of the condition.
Candidates draft comments from memory of the walkthrough rather than from notes taken at the component, so the specifics are lost by the time the report is written.
What to do instead
Take notes at each component in a fixed format: location, what was observed, how it was observed, and why it matters. Build the report comment from those notes so every conclusion is traceable to a described observation. Read each comment back and ask whether a client who was not present could picture the condition.
Presenting recommendations as instructions to perform repairs - specifying a fastener size, a repair method, or a product - instead of describing the condition and directing the client to a qualified professional.
Candidates want to be helpful and demonstrate expertise, and the line between 'this is defective' and 'here is how to fix it' is easy to cross when the defect has an obvious remedy.
What to do instead
Separate observation from recommendation. State the condition and its implication, then recommend evaluation or correction by a qualified contractor or engineer without prescribing means and methods. Review the report for any sentence that tells someone how to build or repair, and rewrite it as a referral.
Describing items that were not actually observed as if they were inspected - for example, reporting the ledger flashing as properly installed when it was concealed by siding.
Candidates fill in blanks from expectation: the flashing is usually there, the deck usually has lag bolts, so the report says so. This is the most serious reporting error because it misrepresents the scope of the inspection.
What to do instead
Maintain an explicit vocabulary for the three states: observed and acceptable, observed and defective, and not observed. Use 'not visible' or 'concealed' language consistently and explain the limitation. Before delivering the report, scan for any statement of condition on an element you cannot recall actually seeing.
Omitting the limitations and scope language specific to the deck - access limitations, areas not walked, weather or storage conditions, and the fact that concealed framing was not evaluated.
Candidates treat the boilerplate scope section as sufficient and do not add the deck-specific limitations that arose during this particular inspection.
What to do instead
Record limitations as they occur during the walkthrough, not afterward. Include deck-specific statements: which sides were accessible, whether the underside was visible, what was stored on the deck, and what concealed conditions remain unknown. Tie each limitation to the affected component so the client understands its practical effect.
Failing to prioritize findings - listing a loose baluster and a detached ledger in the same flat list with the same tone, so the client cannot tell which condition is urgent.
Candidates write the report in the order they walked the deck rather than in the order of consequence, and they avoid ranking because they fear appearing to make engineering judgments.
What to do instead
Organize or summarize findings by severity, and describe the consequence of each: a ledger attachment deficiency affects the whole deck's connection to the structure, while a loose baluster affects one opening. Describing consequence is not an engineering opinion; it is the reason the client should act, and it can be stated without prescribing a repair.