What a checklist cannot tell you, and where buyers get hurt

Presence and absence against condition

A checklist records whether a thing is there. An inspection records a judgment about whether it works, and those are not the same question. Every box on every checklist ever printed answers the first; essentially every decision a buyer makes turns on the second.

The standards make the distinction explicit. ASHI defines inspect as “the process of examining readily accessible systems and components by (1) applying this Standard, and (2) operating normal operating controls, and (3) opening readily openable access panels.” Three verbs, two of which involve touching the house. A printed page does none of them.

What follows is the gap: what the access rules exclude from any visual inspection, what concealment hides from both, what needs a different license entirely, and the items where a checkbox and a finding diverge.

What "readily accessible" actually excludes

Every standard limits the inspection to what is readily accessible, and the definitions are not the same. Massachusetts’s is materially narrower, and the difference is one clause long.

In Massachusetts, anything an inspector would need a portable ladder to reach is outside readily accessible by definition: the roof, the gutters, parts of the eaves, a high attic hatch. Under the ASHI and Illinois wording a ladder is permitted but never required — InterNACHI separately states an inspector need not walk any roof surface. So a Massachusetts buyer assuming the roof was reached is assuming something their state’s regulation does not support.

The other half of the definition is about the seller’s belongings, and personal property stops an inspection in every jurisdiction above. A full garage, a closet in front of an attic hatch, boxes over a crawlspace entry — each converts a required inspection into a non-inspection, and the only honest checklist entry is a blank.

Concealed conditions: invisible to both

Nothing behind a finished surface is in scope, and this is the one limit a checklist and an inspection share exactly.

InterNACHI’s limitations state that an inspection “will not identify concealed or latent defects.” ASHI’s state that inspections “are not technically exhaustive” and are not required to identify “concealed conditions, latent defects, consequential damages.” Arizona’s adopted standards use nearly identical words. Texas states it most flatly: nothing buried, hidden, latent, or concealed.

Two consequences worth being blunt about. A clean report is not a statement that the house is sound — it is a statement about what was visible on one day through one set of eyes. And a defect found after closing, inside a wall, is usually not evidence the inspection failed; in most cases it is evidence the inspection worked as every standard defines it.

What needs an engineer rather than an inspector

There is a hard line in the standards, and it falls at the word adequacy.

InterNACHI’s structural section requires the inspector to report indications of foundation movement, active water penetration and wood in contact with soil. The same section states the inspector need not determine the adequacy of the foundation, identify joist sizing, assess the adequacy of the structural system, or “provide any engineering or architectural service.” ASHI likewise excludes architectural and engineering services and warranties, and Arizona’s board says inspectors need not “calculate the strength, adequacy, or efficiency of any system.”

So a structural finding has a fixed shape: here is an observation, and here is a referral. The inspector may tell you a thing is there and is barred from telling you whether it is a problem. The same wall stands around causation — InterNACHI’s exclusions relieve the inspector of determining “the cause of any condition,” so the question every buyer asks about a crack is outside the scope of the person standing in front of it.

Oregon has the clearest vocabulary for the handoff, requiring a recommendation to “monitor, evaluate, repair, replace or other appropriate action.” Evaluate describes not a defect but a question the inspection was not permitted to answer. A checklist has no equivalent: there is no box meaning this needs a structural engineer, which is the finding that most often decides whether a purchase works.

Four things a checklist marks present and an inspector would flag

Specific cases, each with the rule that produces the divergence.

Smoke and carbon monoxide alarms. A checklist ticks them present. The standard requires the inspector to inspect them and to report their absence, and separately covers venting systems and fuel-burning appliances — which is where the risk sits. CPSC estimated 204 non-fire consumer-product carbon monoxide deaths in 2021, published February 2025, of which heating systems accounted for 63 and water heaters for 4; an estimated 86 percent resulted from exposure in a home location. An alarm present is a tick; whether the appliance vents correctly is an inspection.

The water heater that produces hot water. A checklist ticks hot water: yes, and so, in effect, does the standard — InterNACHI’s plumbing section expressly does not require measuring the capacity, temperature, age, life expectancy or adequacy of the water heater. CPSC’s Publication 5098 from 2012 gives exposure times to a third-degree burn: two seconds at 150°F, a six-second exposure at 140°F, thirty seconds at 130°F, five minutes at 120°F — the temperature the Commission recommends. Most tap water scald injuries and deaths are to the elderly and to children under five. This is the rare case where the right move is to check it yourself with a thermometer, because neither document will — and the number that matters is the one at the tap, not the one on the dial.

The sump pump that is present. Here both tools stop. A checklist ticks it present; the standard states the inspector is not required to operate sump pumps. Unless your inspector volunteers that they ran it, nobody has confirmed it runs.

Solid aluminum branch wiring. No checklist has a box for this. The standard requires the inspector to report its presence, alongside the absence of detectors — the only two conditions in the electrical section singled out for mandatory reporting. The items that matter most are the ones nobody thought to put on a list.

What the injury data shows, phrased correctly

The Consumer Product Safety Commission publishes national estimates of emergency department-treated injuries by product category. The home-structure categories for calendar year 2024:

Read that table carefully, because it is routinely misread. These are injuries associated with a product category, not injuries caused by defects. A stair injury is counted whether the stair was defective, perfectly built, or irrelevant to what happened. Nobody may say defective stairs injured 2.4 million people. They are also weighted national estimates from a sample, carrying sampling error, not counts.

What the table supports is a ranking of where injuries in homes happen: circulation surfaces first by an enormous margin, then the things people walk into, then the raised structures and the glazing, then the railings. A separate Commission report, published April 2026 for injuries occurring in 2024, puts stairs, ramps, landings and floors at “over 3.0 million emergency department-treated injuries and over 7.7 million medically attended injuries” annually — a wider measure from a different publication, which is why both should carry their source.

One caution, because this subject is where bad statistics breed. A widely circulated figure — 224,000 deck and porch injuries, nearly 15 percent attributed to structural failure or collapse — is cited across the inspection industry as a government study. It is not. It is a private company’s 2010 analysis of Commission data covering 2003 to 2007, and the only copy we could locate sits on an inspection company’s website rather than the author’s. Use the Commission’s own 2024 figures instead.

What neither a checklist nor an inspection will tell you

Some gaps do not close by hiring someone. These are excluded from the inspection too, and a buyer who does not know it will spend the contingency period asking for the wrong things.

How long anything has left. Excluded by ASHI, InterNACHI, Texas rule and the Arizona board, which also excludes predicting “future conditions, including but not limited to failure of components.”

Whether it meets code. Excluded by Texas, Arizona and InterNACHI. What a municipal permit inspection covered is a different record from a different body — what the city inspected is a separate question.

What it is worth, whether it is insurable, whether to buy it. Market value, marketability, insurability and the advisability of purchase are excluded by name in both national standards.

What repairs will cost. Excluded by InterNACHI, and Arizona’s board relieves inspectors of reporting on “the methods, materials and costs of corrections.” A repair figure in a report is a courtesy from someone not bidding the work.

Environmental conditions. Mold, fungus, asbestos, air quality, radon, pests, hazardous waste and electromagnetic fields are excluded by both standards and by Arizona’s, and HUD’s buyer notice names most of them as needing separate specialist testing.

And the inspection has its own failure rate. A nonprofit consumer research publisher ran an undercover test of twelve inspectors in a single metropolitan market in 2018 against 28 problems it judged any inspector should catch. As a group, they caught them about half the time. That is a small, dated, one-market study and must never be read as a national detection rate — but it is the only measurement of its kind we could locate, and it argues against treating any single document as the last word.

What to do with all of this

Use a checklist for what it is good at and stop there: a consistent basis for comparing houses, a prompt for a maintenance round, a record of condition at the start of a tenancy. Two free institutional ones exist and are worth printing.

For the decision itself, work from the standards. Ask the inspector which one they work to and read it before the day — a federal form tells buyers to ask for exactly that. Know what is required and what is excluded in each area before you walk it, and carry questions rather than boxes.

Then, when the report arrives, read the not-inspected entries first. They are the checklist entries that stayed blank, written down by a professional required to say why — and they are the closest thing anyone will give you to a map of what is still unknown about the house.

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