You're paying $500-$700 for a home inspection. Ever wonder what the inspector is actually doing during those three hours? What tools are they using? What are they looking for? How do they decide what's a problem and what's not?
This article pulls back the curtain on the home inspection profession. It's not essential knowledge for buying a home (see Home Inspection What to Expect for that), but if you're curious about the technical side or want to understand your home from an insider's perspective, this is for you.
What you'll learn:
- The professional standards inspectors follow
- Tools and equipment inspectors use
- How inspectors evaluate each major system
- What "red flags" look like to professionals
- Why inspectors can't predict the future
- How inspection methodology differs from code compliance
- The science behind moisture detection and thermal imaging
This article is for: Curious buyers who want to understand the technical aspects of inspection, or homeowners who want to see their property through an inspector's eyes.
Table of Contents
- Professional Standards and Methodology
- The Inspector's Toolkit
- Structural Inspection Methodology
- Electrical System Evaluation
- Plumbing System Analysis
- HVAC System Inspection
- Moisture Detection and Management
- Roof Inspection Techniques
- Understanding Inspection Limitations
- Report Writing and Documentation
- Summary: The Inspector's Perspective
- Related Articles
Professional Standards and Methodology
Standards of Practice: ASHI vs InterNACHI
Home inspectors don't make up their own rules. They follow established Standards of Practice (SOP) that define what they must inspect, how they inspect it, and what they report.
ASHI (American Society of Home Inspectors):
- Oldest professional organization (founded 1976)
- Conservative, well-defined scope
- Requires 250 paid inspections for membership
- Continuing education mandatory
InterNACHI (International Association of Certified Home Inspectors):
- Larger membership base
- More comprehensive SOP
- Includes more systems and components
- Online training and certification
What both require:
- Visual examination of accessible areas
- Non-invasive testing only
- Report on condition, not value
- Identify safety hazards
- Note defects in major systems
What both prohibit:
- Destructive testing (opening walls, moving insulation)
- Predicting future failures
- Estimating repair costs
- Performing repairs themselves
- Guaranteeing code compliance
Seattle context: Most Seattle inspectors follow InterNACHI standards, which include more detailed requirements for moisture inspection (critical in PNW climate).
The "Snapshot in Time" Limitation
Inspectors evaluate the home's condition on inspection day only. They can't predict:
- When a working system will fail
- Hidden problems behind walls
- Issues that develop after inspection
- Seasonal problems (if inspected in summer, can't see winter ice dams)
Example: A 20-year-old water heater might work perfectly during inspection but fail the next week. The inspector notes its age and recommends budgeting for replacement, but can't predict when it will fail.
Visual vs Invasive: What Inspectors Can't Do
Can do:
- Look at visible components
- Test operation of systems
- Use moisture meters on surfaces
- Take thermal images
- Operate switches and valves
Can't do:
- Move stored items or furniture
- Open walls or ceilings
- Dig around foundation
- Remove insulation
- Access dangerous areas
- Test every outlet (sample only)
Why: Inspectors can't damage the property or create liability. If they moved your boxes and broke something, who's responsible?
Liability and Insurance Considerations
Inspectors carry Errors & Omissions (E&O) insurance, but it has limits:
- Typically covers only inspection fee (not repair costs)
- Requires proof inspector was negligent
- Doesn't cover things outside SOP
- Doesn't cover inaccessible areas
This is why: Inspectors are conservative in their reports. They'd rather flag something minor than miss something major and face a lawsuit.
The Inspector's Toolkit
Basic Equipment Every Inspector Carries
Flashlight (high-powered):
- Illuminates dark crawlspaces, attics
- Reveals details in shadows
- Essential for electrical panel inspection
Moisture meter:
- Detects moisture in wood, drywall
- Two types: pin-type (invasive) and pinless (surface)
- Critical in Seattle's wet climate
Electrical tester:
- Tests outlet wiring and grounding
- Checks GFCI function
- Identifies reversed polarity
Ladder:
- Access to roof (if safe)
- Attic hatch access
- High areas
Screwdrivers and basic tools:
- Remove electrical panel cover
- Open access panels
- Test operation of components
Camera:
- Document all findings
- Before/after comparisons
- Evidence for report
Inspection software/tablet:
- Digital report generation
- Photo integration
- Standardized checklists
Advanced Tools: Thermal Imaging
Thermal camera (FLIR):
- Detects temperature differences
- Reveals hidden moisture
- Identifies missing insulation
- Spots electrical hot spots
- Finds air leaks
How it works:
- Infrared radiation detection
- Color-coded temperature map
- Warmer areas show red/yellow
- Cooler areas show blue/purple
What it reveals:
- Wet insulation (shows cooler)
- Missing insulation (temperature variation)
- Air leaks around windows/doors
- Overheating electrical components
- Radiant heat loss
Limitations:
- Doesn't see through walls
- Affected by surface materials
- Requires temperature differential
- Can't identify moisture source
Seattle application: Particularly useful for detecting moisture intrusion in walls, a common PNW problem.
Specialized Equipment for Specific Systems
Sewer scope camera:
- Not part of standard inspection
- Separate service ($300-$500)
- Fiber optic camera on cable
- Records video of sewer line
- Identifies roots, cracks, bellies
Gas leak detector:
- Electronic "sniffer"
- Detects natural gas or propane
- More sensitive than smell
- Checks around appliances, connections
Carbon monoxide detector:
- Portable unit
- Tests near fuel-burning appliances
- Identifies dangerous CO levels
- Critical safety check
Combustion analyzer:
- Tests furnace efficiency
- Measures exhaust gases
- Identifies incomplete combustion
- Advanced tool, not all inspectors carry
Structural Inspection Methodology
Foundation Evaluation Techniques
What inspectors look for:
- Cracks (width, location, pattern)
- Settlement indicators
- Water intrusion signs
- Proper drainage
- Structural support
Crack assessment:
- Hairline cracks (<1/8"): Usually cosmetic
- 1/8" to 1/4": Monitor, may need repair
- >1/4": Structural concern, engineer needed
- Horizontal cracks: More serious than vertical
- Stair-step cracks in block: Settlement issue
Tools used:
- Crack gauge (measures width)
- Level (checks for slope)
- Moisture meter (checks for water)
- Flashlight (examines details)
Seattle-specific concerns:
- Unbolted foundations (seismic risk)
- Moisture in crawlspaces (common)
- Settling on hillside properties
- Inadequate drainage
Framing and Structural Support Assessment
What inspectors examine:
- Load-bearing walls
- Beams and joists
- Proper support under loads
- Modifications and cuts
- Sagging or deflection
Red flags:
- Cut or notched joists
- Missing support posts
- Sagging floors or ceilings
- Cracks at stress points
- Improper modifications
How they check:
- Visual examination
- Marble test (rolls on floor to show slope)
- Laser level (measures deflection)
- Probing for soft spots
When to call engineer:
- Significant sagging (>1" over 20')
- Large cracks in load-bearing walls
- Obvious structural modifications
- Signs of movement or failure
Roof Structure Inspection
Attic examination:
- Rafter condition
- Proper bracing
- Ventilation adequacy
- Insulation condition
- Signs of leaks
What they look for:
- Water stains on rafters
- Mold or mildew
- Proper ventilation (soffit to ridge)
- Adequate insulation (R-38 to R-49 in Seattle)
- Proper attic access
Ventilation calculation:
- 1 sqft vent per 150 sqft attic space
- Or 1 sqft per 300 sqft with vapor barrier
- Balanced intake (soffit) and exhaust (ridge)
Seattle concern: Inadequate ventilation leads to moisture buildup and mold, common in older homes.
Electrical System Evaluation
Service Panel Inspection Protocol
What inspectors check:
- Panel type and brand
- Service capacity (amps)
- Proper labeling
- Wire condition
- Signs of overheating
- Proper grounding
Red flag panels:
- Federal Pacific (FPE): Known fire hazard
- Zinsco: Breakers don't trip properly
- Pushmatic: Obsolete, parts unavailable
- Rust or corrosion
- Burn marks or melted components
How they inspect:
- Remove panel cover (if safe)
- Visual examination of connections
- Check for double-taps (two wires on one breaker)
- Verify proper wire sizing
- Test main breaker operation (sometimes)
Service capacity assessment:
- 60-100 amp: Undersized for modern homes
- 100-150 amp: Adequate for most homes
- 200 amp: Standard for new construction
- Calculate load vs capacity
Seattle context: Many older Seattle homes have 60-100 amp service, inadequate for modern electrical loads (EVs, heat pumps, etc.).
Circuit and Wiring Evaluation
What they test:
- Outlet wiring (hot, neutral, ground)
- GFCI protection (bathrooms, kitchen, exterior)
- AFCI protection (bedrooms in newer homes)
- Grounding system
- Wire types and condition
Testing procedure:
- Plug-in tester at sample outlets
- GFCI test button
- Visual inspection of visible wiring
- Check for aluminum wiring
- Verify proper wire gauge
Common issues found:
- Reversed polarity (hot and neutral swapped)
- Missing ground
- Non-functioning GFCI
- Aluminum wiring (fire hazard if not properly maintained)
- Knob-and-tube wiring (pre-1950s)
Aluminum wiring concerns:
- Used 1965-1973
- Expands/contracts more than copper
- Connections loosen over time
- Fire hazard if not maintained
- Requires special connectors (COPALUM)
Identifying Electrical Hazards
Immediate safety concerns:
- Exposed wiring
- Burn marks in panel
- Overheated breakers
- Improper grounding
- Water near electrical
How inspectors identify:
- Visual inspection
- Thermal imaging (hot spots)
- Smell (burning plastic)
- Outlet tester results
- Panel examination
Documentation:
- Photos of hazards
- Thermal images if available
- Specific location notes
- Recommendation for licensed electrician
Plumbing System Analysis
Water Supply System Inspection
What inspectors check:
- Pipe materials and condition
- Water pressure
- Supply line leaks
- Shut-off valves
- Cross-connections
Pipe material assessment:
- Copper: Good, long-lasting
- PEX: Modern, flexible, good
- Galvanized steel: Old, corrodes, replace
- Polybutylene (gray plastic): Failed system, replace
- CPVC: Acceptable but brittle
Water pressure testing:
- Normal: 40-80 PSI
- Low (<40 PSI): Poor performance
- High (>80 PSI): Needs pressure reducer
- Tool: Pressure gauge on hose bib
Seattle-specific:
- Many older homes have galvanized pipes
- Polybutylene common in 1980s-1990s homes
- High water pressure in some areas (needs reducer)
Drain, Waste, and Vent (DWV) Evaluation
What they check:
- Drain function (all fixtures)
- Vent system adequacy
- Trap configuration
- Cleanout access
- Signs of leaks or backups
Testing procedure:
- Run water in all fixtures
- Check drain speed
- Look for gurgling (vent issue)
- Inspect visible pipes
- Check for proper slope
Common issues:
- Slow drains (partial blockage)
- Gurgling (vent problem)
- S-traps (not code compliant)
- Missing cleanouts
- Improper slope
Sewer line concerns:
- Not part of standard inspection
- Recommend sewer scope for pre-1980 homes
- Clay pipes deteriorate
- Root intrusion common
- Bellied or collapsed sections
Water Heater Assessment
What inspectors evaluate:
- Age (check serial number)
- Capacity (gallons)
- Fuel type (gas, electric, tankless)
- Proper installation
- Safety features
- Signs of leaks
Age determination:
- Serial number contains manufacture date
- Varies by manufacturer
- Typical lifespan: 8-12 years
- Recommend replacement if >10 years
Safety checks:
- Temperature/pressure relief valve
- Proper venting (gas units)
- Earthquake straps (required in Seattle)
- Drip pan (if in living space)
- Proper clearances
Red flags:
- Rust or corrosion
- Water pooling at base
- Improper venting
- Missing safety features
- Very old unit
HVAC System Inspection
Heating System Evaluation
What they test:
- System operation
- Heat output
- Thermostat function
- Safety features
- Ductwork condition
Testing procedure:
- Turn on system
- Verify heat at registers
- Check temperature rise (15-25°F typical)
- Listen for unusual noises
- Inspect visible components
Furnace-specific checks:
- Heat exchanger condition (if visible)
- Burner operation
- Flame appearance (blue, steady)
- Proper venting
- Filter condition
Heat pump checks:
- Compressor operation
- Refrigerant lines condition
- Defrost cycle function
- Backup heat operation
- Age and efficiency
Seattle context: Many homes have electric baseboard heat (no ductwork), heat pumps increasingly common for efficiency.
Cooling System Assessment
What they check:
- Compressor operation
- Refrigerant lines
- Condensate drain
- Temperature drop (15-20°F typical)
- Age and condition
Testing limitations:
- Can't test if outdoor temp <65°F
- Risk of compressor damage
- Note in report if not tested
Common issues:
- Refrigerant leaks
- Clogged condensate drain
- Dirty coils
- Old system (15+ years)
Seattle note: Many older Seattle homes lack AC. Inspectors note this but don't flag as defect (not required by code).
Ductwork and Ventilation Inspection
What they examine:
- Duct condition (visible portions)
- Proper insulation
- Air leaks
- Ventilation adequacy
- Filter access
Common issues:
- Disconnected ducts
- Missing insulation
- Crushed or damaged ducts
- Inadequate return air
- Dirty or missing filters
Ventilation requirements:
- Bathroom exhaust fans
- Kitchen range hood
- Dryer vented outside
- Combustion air for furnace
Moisture Detection and Management
The Science of Moisture Meters
How they work:
- Pin-type: Measures electrical resistance
- Pinless: Measures electromagnetic field
- Higher moisture = lower resistance
- Readings in "wood moisture equivalent" (WME)
Reading interpretation:
- 0-15% WME: Normal, dry
- 16-19% WME: Elevated, monitor
- 20-24% WME: High, likely problem
- 25%+ WME: Very high, active moisture
Limitations:
- Surface reading only
- Affected by material type
- Can't identify moisture source
- False positives possible (metal, salts)
Seattle application: Critical tool in PNW. Inspectors check crawlspaces, bathrooms, around windows, and any suspicious areas.
Thermal Imaging for Moisture Detection
How it reveals moisture:
- Wet materials are cooler (evaporation)
- Shows as blue/purple on thermal image
- Reveals patterns invisible to eye
- Identifies extent of problem
What it can find:
- Roof leaks
- Plumbing leaks
- Condensation issues
- Missing vapor barriers
- Air leaks (related to moisture)
Limitations:
- Doesn't see through walls
- Requires temperature differential
- Can't identify source
- Needs interpretation skill
Example: Thermal image shows cool spot on ceiling. Moisture meter confirms high reading. Likely roof leak, but could be plumbing or condensation. Further investigation needed.
Identifying Moisture Sources
Common sources:
- Roof leaks
- Plumbing leaks
- Condensation
- Poor drainage
- Groundwater intrusion
- Inadequate ventilation
How inspectors determine source:
- Location of moisture
- Pattern of damage
- Related symptoms
- Exterior examination
- Attic/crawlspace inspection
Seattle-specific sources:
- Poor gutter maintenance
- Inadequate crawlspace ventilation
- Window condensation (single-pane)
- Deck attachment leaks
- Hillside drainage issues
Roof Inspection Techniques
Safe Roof Access and Evaluation
When inspectors walk roof:
- Low-slope roofs (safe to walk)
- Good weather conditions
- Proper safety equipment
- Roof appears sound
When they don't:
- Steep pitch (>6/12)
- Wet or icy conditions
- Fragile materials (old wood shakes)
- Safety concerns
- Inspect from ladder or ground
What they look for:
- Shingle condition
- Flashing integrity
- Chimney condition
- Vent penetrations
- Moss or debris
Identifying Roof Problems
Shingle issues:
- Missing or damaged shingles
- Curling or cupping
- Granule loss (bare spots)
- Cracked or broken
- Improper installation
Flashing problems:
- Rust or corrosion
- Gaps or separations
- Missing or damaged
- Improper installation
- Caulk instead of proper flashing
Age assessment:
- Composition shingles: 20-25 years typical
- Wood shakes: 25-30 years
- Metal: 40-70 years
- Tile: 50+ years
- Check permit records for installation date
Seattle concerns:
- Moss growth (common, shortens life)
- Algae staining
- Inadequate ventilation
- Ice dam potential (rare but possible)
Attic Inspection for Roof Issues
What they look for:
- Water stains on rafters
- Active leaks
- Mold or mildew
- Proper ventilation
- Insulation condition
Ventilation assessment:
- Soffit vents (intake)
- Ridge vents or gable vents (exhaust)
- Proper airflow
- No blocked vents
Insulation evaluation:
- Depth (R-value)
- Even coverage
- No compression
- Proper installation
- Vapor barrier present
Understanding Inspection Limitations
What Inspectors Can't See
Behind walls:
- Wiring condition
- Plumbing pipes
- Insulation
- Structural framing
- Hidden damage
Under floors:
- Subfloor condition
- Joist condition
- Plumbing under slab
- Foundation (if finished basement)
In inaccessible areas:
- Blocked crawlspaces
- Locked rooms
- Areas with stored items
- Dangerous locations
Buried or underground:
- Sewer lines
- Foundation below grade
- Underground utilities
- Septic systems
Why Inspectors Can't Predict Failures
Working systems can fail:
- 20-year-old water heater works today, fails tomorrow
- Furnace operates fine, heat exchanger cracks next month
- Roof looks OK, leaks during next heavy rain
Inspectors note:
- Age of systems
- Typical lifespan
- Condition observed
- Recommend budgeting for replacement
They can't predict:
- When failure will occur
- How long system will last
- Future maintenance costs
- Hidden problems
The Difference Between Inspection and Code Compliance
Inspectors evaluate:
- Safety
- Function
- Condition
- Typical practice
They don't evaluate:
- Code compliance (not their job)
- Permit history
- Legal compliance
- Zoning issues
Why: Building codes change over time. A 1950s house wasn't built to 2025 code, but that doesn't make it defective. Inspectors note safety issues and functional problems, not code violations.
Example: Two-prong outlets (no ground) don't meet current code but were legal when installed. Inspector notes lack of grounding as safety concern, not code violation.
Report Writing and Documentation
How Inspectors Organize Findings
Typical report structure:
- Summary (most important)
- System-by-system details
- Photos of issues
- Recommendations
Finding categories:
- Safety hazard (immediate danger)
- Major defect (expensive, important)
- Minor defect (needs attention)
- Maintenance item (routine upkeep)
- Informational (FYI only)
Why this matters: Helps buyers prioritize. Not all findings are equal.
Photography and Evidence Standards
What inspectors photograph:
- All defects found
- Safety hazards
- System conditions
- Overall property
- Specific details
Photo quality:
- Clear, well-lit
- Shows context
- Includes close-ups
- Labeled in report
Why photos matter:
- Visual evidence
- Helps contractors estimate
- Documents condition
- Supports negotiations
Professional Language and Disclaimers
Inspectors use careful language:
- "Recommend evaluation by specialist"
- "Appears to be"
- "Visible portions"
- "At time of inspection"
Why: Protects from liability. They can only report what they see, when they see it.
Common disclaimers:
- "Not all outlets tested"
- "Inaccessible areas not inspected"
- "Cosmetic issues not reported"
- "Not a code compliance inspection"
Summary: The Inspector's Perspective
Home inspectors follow professional standards that define what they inspect and how they report it. They use specialized tools (moisture meters, thermal cameras, electrical testers) to evaluate visible, accessible components of the home.
Inspectors can't see through walls, predict future failures, or guarantee code compliance. They provide a snapshot of the home's condition on inspection day, identifying safety hazards, defects, and maintenance needs.
Understanding inspection methodology helps you interpret reports more effectively and know when additional specialist evaluation is needed. Inspectors are generalists who identify problems; specialists (structural engineers, electricians, roofers) provide detailed solutions.
The inspection is your best protection when buying, but it has limits. Knowing what inspectors can and can't do helps you set realistic expectations and make informed decisions.
Related Articles
- Home Inspection What to Expect - Complete buyer's guide to inspections
- Inspection Responses - How to negotiate based on findings
- Spotting Issues During Tours - What to look for before inspection
- Home Construction Basics - Understanding how homes are built
Disclaimer: This article provides general information about home inspection methodology for educational purposes. It is not a substitute for professional home inspection services. Always hire a qualified, licensed inspector for property evaluation. Inspection standards and practices may vary by location and professional organization.