What Does a Home Inspection Actually Check? 10 Surprising Things

The first house I almost bought had a perfect facade—fresh paint, new countertops, and a basement that smelled like lemon cleaner. The seller’s agent smiled as we walked through. But my home inspector, a grizzled guy named Dave who wore a tool belt like a gunslinger, spent four hours poking corners I never would have thought to check. His report came back with a single photo that made my stomach drop: a slow, hidden drip from a pipe behind the drywall in the guest bathroom, which had already stained the subfloor. That leak had been invisible to everyone, including me, for years. It cost an estimated $4,000 to fix. And that’s just one of the surprises he flagged.

Most buyers think a home inspection checks the obvious: roof, foundation, furnace. But the real value hides in the oddball details that can save you thousands or reveal a money pit. In this article, I’ll walk you through everything a home inspection actually checks—including 10 specific things that often catch buyers off guard. Whether you’re shopping for your first home or your fifth, knowing these will help you ask smarter questions on inspection day.

1. The Obvious Big Stuff (Roof, Foundation, HVAC)

Let’s start with the basics, because every buyer expects these. A thorough home inspection covers the major systems that keep a house livable: the roof, the foundation, the heating and cooling (HVAC), the electrical panel, and the plumbing. Your inspector will climb onto the roof (if it’s safe) to look for missing shingles, curling edges, and signs of leaking around chimneys or vents. They’ll check the foundation for cracks, bowing walls, or water intrusion. They’ll test the furnace and air conditioner—turning them on, checking temperature differentials, and inspecting for rust or unsafe gas connections. The electrical panel gets opened to verify proper breakers, no double-tapped neutrals, and no aluminum wiring in older homes. Plumbing includes running water to check pressure, looking for leaks under sinks, and flushing toilets to see if they drain properly.

These are the non-negotiables. But here’s the truth: most houses pass these checks without major drama. The real surprises hide in the details—and that’s where the 10 items below come in.

2. The 10 Surprising Things Your Inspector Might Flag

In my own inspection experience—and from talking to dozens of inspectors—here are the unexpected items that pop up most often. Each one can derail a sale or give you negotiating power, so pay attention.

1. Improper Electrical Wiring (Especially DIY Work)

This is the single most common surprise, according to the American Society of Home Inspectors. Think ungrounded outlets, reversed polarity, or—my favorite—a light switch that controls nothing because someone wired it to a removed fixture. Inspectors use a simple three-light tester to catch these. If you see a report with “open ground” or “hot/neutral reversed,” that’s a red flag.

2. Missing or Improper GFCI Outlets

Ground Fault Circuit Interrupter outlets are required near water—kitchens, bathrooms, garages, and outdoors. I once inspected a 1980s home where the bathroom outlet was a standard two-prong with a three-prong adapter glued on. That’s a shock hazard. Inspectors check every outlet within six feet of a sink or water source.

3. Roof Flashing Details Gone Wrong

The roof itself might look fine, but the flashing around chimneys, skylights, and vents is where leaks start. Inspectors poke at these edges with a flashlight. I’ve seen flashing that was simply caulked over rust, or missing entirely at a valley. That can lead to hidden rot in the attic.

4. Attic Insulation Depth and Ventilation

Most buyers never climb into the attic. But inspectors do. They measure insulation depth (R-value) and check for proper soffit vents, ridge vents, or gable vents. I once found an attic so poorly ventilated that the roof deck had black mold from trapped moisture. The seller had to replace the entire roof deck—a $6,000 surprise.

5. Grading and Drainage Around the Foundation

Inspectors walk the perimeter looking for soil that slopes toward the house instead of away. Even a slight negative slope can funnel rainwater against the foundation, causing cracks and basement leaks. They also check downspout extensions—if water is dumping right next to the wall, that’s a problem.

6. Functional Flow of Plumbing Fixtures

It’s not just about leaks. Inspectors time how long it takes hot water to reach a far bathroom. If it’s more than 60 seconds, that suggests poor pipe sizing or a long run that wastes water. They also check for cross-connections (where hot and cold pipes might mix) and water pressure issues.

7. Window and Door Operation

You might think this is cosmetic, but stuck or misaligned windows can indicate foundation settling, and doors that don’t latch properly can mean the frame shifted. Inspectors open and close every operable window and door. I once flagged a sliding glass door that was so warped it wouldn’t lock—security risk.

8. Gas Line Connections and Venting

For homes with gas stoves, furnaces, or water heaters, inspectors check that the gas shutoff valve is accessible and that the vent pipe is properly connected and not rusted. A disconnected gas line can leak carbon monoxide. I saw one where the vent was stuffed with a rag—the homeowner had tried to stop a draft but created a deadly hazard.

9. Water Heater Age and TPR Valve

The temperature-pressure relief (TPR) valve is a small safety device on the water heater that prevents explosions. Inspectors test it by lifting the lever (though they warn you it may not reseat). They also note the manufacture date—anything over 10 years old is near the end of its life. I’ve flagged units that were 18 years old and corroded.

10. Pest and Critter Evidence (Visual Only)

Inspectors aren’t exterminators, but they look for signs of rodents, termites, or carpenter ants: droppings, gnawed wood, mud tubes, or nests. I once found a squirrel nest in an attic soffit vent—the inspector noted it as a “potential entry point.” That led to a separate pest inspection that cost $150 but saved me from a $3,000 repair.

3. What Inspectors Don’t Check (And Why That Matters)

Here’s the honest truth: a standard home inspection has clear limits. Your inspector won’t test for mold, radon, asbestos, lead paint, or pests unless you pay for add-ons. They won’t inspect the sewer line unless you request a video scope. They won’t move furniture, lift rugs, or open walls. If a leak is hidden behind a finished basement wall, they may only detect it with a moisture meter if they suspect it—but they won’t tear anything apart.

This matters because buyers often assume the inspection covers everything. I’ve seen people waive a sewer scope only to discover a collapsed pipe after closing—a $5,000 mistake. The InterNACHI standards of practice explicitly state that inspectors report only visible and accessible conditions. Always ask what’s not included and decide what add-ons make sense for your house (older homes, for example, often benefit from radon testing and sewer scopes).

4. How to Prepare for a Home Inspection (And Save Money)

I’ve been on both sides of the inspection—as a buyer and as a seller. Here are practical steps that actually help, based on what inspectors tell me they wish homeowners knew.

• Clear access: Move boxes, furniture, and clutter away from the furnace, water heater, electrical panel, and attic hatch. Inspectors need a clear path. I once had to reschedule because the seller’s storage blocked the attic access.
• Turn on utilities: Make sure the gas, water, and electricity are on. A “no power” inspection is essentially useless.
• Fix obvious safety hazards: Replace burned-out light bulbs, fix loose handrails, and secure any exposed wiring. These small fixes can prevent minor flags that still show up on the report.
• Disclose known issues: If you know the roof leaks or the furnace is old, tell the inspector ahead of time. They’ll still check it, but honesty builds trust and prevents a surprise that kills the deal.
• Attend the inspection: Follow the inspector around. Ask questions. I did this on my first house and learned more in three hours than I had in months of reading. It’s the best $500 you’ll spend on education.

By preparing, you reduce the chance of minor findings turning into deal-killers. And if you’re the buyer, you’ll know exactly where to negotiate—focus on safety and structural issues, not cosmetic nits like a chipped tile.

Frequently Asked Questions

How long does a typical home inspection take?

Most inspections run 2 to 4 hours, depending on the size, age, and condition of the home. A 1,500-square-foot house in good shape might take 2.5 hours; an older 3,000-square-footer could take 4.

Can a home inspection find hidden mold?

Only if it’s visible or accessible. Inspectors don’t test for mold unless you pay for a specialized add-on. If they see discoloration or moisture, they’ll flag it and recommend a mold inspection.

Do I need to attend the home inspection?

Yes—strongly recommended. Being there lets you ask questions and see issues firsthand. I’ve learned more about a house’s quirks in one inspection than in a dozen walkthroughs.

What's the most common surprise found during an inspection?

Improper electrical wiring, like DIY outlets without GFCI protection, is the top surprise. It’s often cheap to fix but reveals a pattern of shoddy work that might affect other systems.

Should I fix everything the inspector finds before buying?

No. Focus on safety and major structural issues. Minor cosmetic items—like a cracked outlet cover or a loose doorknob—are often negotiable or you can handle them later. Don’t kill a deal over a $50 fix.

Practical takeaway: A home inspection is your best tool for uncovering hidden problems—but only if you know what it actually covers. The 10 surprises above are worth bookmarking before your next inspection. Walk through with your inspector, ask about each one, and you’ll leave with a clear picture of the house’s real condition. That’s the kind of knowledge that can save you thousands and give you peace of mind.