Home inspection red flags that actually matter

Structural and water: the findings that change the decision

Horizontal cracking, stepped cracking through masonry, bowing walls, or displacement between sections of foundation are the only inspection findings that routinely justify walking away, because the cost has a very long tail and cannot be bounded without an engineer. Vertical hairline cracks in poured concrete, by contrast, are near-universal and usually a shrinkage artifact.

Active water intrusion matters more than almost anything cosmetic, because water is the mechanism behind rot, mold, insect damage, and foundation movement. An inspector who reports a damp basement corner, efflorescence on a wall, or staining at a rim joist is describing a system that is currently failing, not a past event.

Grading that slopes toward the house and downspouts discharging at the foundation are the cheapest fix on this entire page and the cause of a surprising share of the expensive findings below them.

• • Horizontal or stepped foundation cracking, or any displacement — get a structural engineer before pricing anything
• • Active moisture, efflorescence, or staining at the rim joist or sill
• • Grading sloped toward the foundation, or downspouts terminating at the wall
• • Sagging floors, or a ridge line in the roof that is visibly deflected
• • Insect damage or rot found in structural framing rather than trim

Electrical: the safety category with the shortest fuse

Electrical findings are the ones to take at face value, because the failure mode is fire rather than expense. Knob-and-tube wiring is the headline item in older housing: it is not inherently dangerous when undisturbed and correctly fused, but it has no ground, it degrades where it has been buried in insulation, and a growing number of insurers simply will not write a policy on a house that still has it energized.

Federal Pacific Stab-Lok and Zinsco panels are named in inspection reports for a reason — both have documented histories of breakers failing to trip. An inspector cannot prove yours is defective, and most electricians will recommend replacement rather than testing.

Aluminum branch wiring from the mid-1960s to mid-1970s is not a replacement job in most cases; it is a connection job, remediated with approved connectors at every device. The cost is far lower than a rewire, and skipping it is not an option.

• • Active knob-and-tube, especially buried in blown-in insulation
• • Federal Pacific Stab-Lok or Zinsco panel
• • Aluminum branch circuit wiring without approved connectors
• • Double-tapped breakers, missing panel bonding, or open splices outside a box
• • No GFCI protection at kitchen, bath, exterior, or garage receptacles

The specialist referrals people skip, and shouldn't

A sewer lateral scan is not part of a standard inspection and is the single finding most likely to turn into a five-figure surprise in the first year of ownership — especially on homes built before 1980, where clay or Orangeburg pipe and mature tree roots meet. It costs a few hundred dollars to rule out.

A chimney is inspected from the ground and the roof surface in a general inspection. The liner, which is where the expensive problems live, requires a Level 2 camera inspection. On any house with an active fireplace or a chimney-vented heating appliance, it is worth the fee.

Radon is a health finding rather than a structural one and is genuinely regional — but mitigation is one of the cheapest and most reliable fixes on this list, so a positive test is a budget item, not a deal-breaker.

What is usually not a red flag

Vertical hairline foundation cracks, worn caulking, doors that stick, a water heater without an expansion tank in a jurisdiction that did not require one, dated but functioning electrical fixtures, and a roof in its late teens with no active leaking. These are all real findings and none of them should be the centre of a negotiation.

Age by itself is also not a defect. A 19-year-old furnace running correctly is a budgeting fact — you will likely replace it within five years — and framing it as a repair request rarely succeeds, because the seller knows the house is priced as a house with a 19-year-old furnace.

Estimated repair cost ranges

What the serious findings cost to address. These are estimated ranges for scale — for anything structural, get an engineer's scope before any price means anything.

• Foundation crack repair: Injection of a non-structural crack is the low end. Anything the report calls horizontal, stepped, or displaced needs a structural engineer before a price means anything.
• Sump pump and perimeter drainage: A pump and a discharge line is the low end; an interior French drain around the full perimeter with a sealed sump is the high end. Regrading and gutter extensions often fix the problem for far less.
• Knob-and-tube removal / rewire: Almost entirely labor, and plaster walls cost far more to fish than drywall. Insurers increasingly will not write a policy with active knob-and-tube, so this one is rarely optional.
• Electrical panel upgrade: Utility coordination, a new mast and meter socket, or moving the panel out of a bathroom or closet are what separate a $2k job from a $6k one.
• Sewer lateral repair or replacement: Trenchless lining is mid-band; open excavation under a driveway or a street cut with a municipal permit is the top. Get a camera scan before agreeing to anything.
• Chimney repair (repoint, crown, liner): Repointing is the low end; a stainless liner or a rebuild above the roofline is the high end. A Level 2 chimney inspection tells you which one you are buying.
• Mold remediation: The remediation is usually the smaller cost. The water source that caused it, and the finishes torn out to reach it, are the real number.
• Radon mitigation system: A slab-on-grade basement with one suction point is straightforward. Fieldstone foundations, crawl spaces needing membrane, and multiple suction points cost more.
• Roof replacement (asphalt shingle): Pitch, layer count, and sheathing found rotten at tear-off are the three things that move this most. Ask for a per-sheet unit price on replacement sheathing before signing.

Frequently asked questions

Keep reading

• What should be in a contractor's estimateThe eleven things a complete contractor estimate spells out — scope, allowances, exclusions, payment schedule, change-order markup — and how to spot the gaps that turn into change orders later.
• How to read a home inspection reportA 40-page inspection report is not a repair list. Here is how to read one in order, separate safety and structure from cosmetics, and turn it into a short list you can act on before your contingency expires.
• What to do after a home inspectionThe inspection is done and the contingency clock is running. Here is the order of operations for the next seven to ten days — what to chase, what to price, what to ask for, and when to walk.
• How to negotiate repairs after a home inspectionHow to turn an inspection report into a repair request a seller will actually accept — what to include, what to leave out, whether to ask for repairs or a credit, and how to price the ask.
• Inspection contingency, explainedWhat an inspection contingency actually protects, how long you get, what happens if the deadline passes, and how waiving it changes your risk — in plain English for buyers under contract.
• What to ask for after a home inspectionA practical list of what belongs in a post-inspection request, what to leave off, how to word each ask, and what the common items cost — so your request reads as reasonable and gets a real answer.
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